Human Factors Literature Reviews on Intersections, Speed Management, Pedestrians and Bicyclists, and Visibility

Accident Analysis of Older Drivers at Intersections
(FHWA–RD–94–021)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Not Specified

Anonymous

1995

5

http://www.tfhrc.gov/safety/hsis/94-021.htm

Crash/Demographics Statistical Analysis

Normal

Not Specified

To examine the specific nature of intersection–related crashes involving elderly drivers through a detailed analysis of crash data from the Highway Safety Information System (HSIS).

The analyses were conducted as part of the FHWA research study, "Traffic Operations Control for Older Drivers." The authors used HSIS data from 1985 to 1987 in Minnesota and Illinois for this research.

• For all of the analyses, comparisons were made among three age groups: (1) "young elderly" (ages 65 to 74), (2) "old elderly" (age 75 and older), and (3) a middle–aged comparison group (ages 30 to 50).
• The crash types at both urban and rural signalized and stop–controlled intersections were examined separately, as well as the type of vehicle maneuver prior to the crash and the investigating officer’s judgment regarding "causal" factors.

Aged Drivers, Intersections, Traffic Accidents, Accident Data, Elderly Drivers, Older Drivers

• The general analyses of crash type in both States indicated that at both urban and rural signalized intersections, elderly drivers were less likely than their middle–aged counterparts to be involved in rear–end collisions, but more likely to be involved in left–turn and angle collisions.

• In both States, right–angle collisions presented a particular problem for elderly drivers at both urban and rural stop–controlled intersections.

• For turning collisions at urban and rural signalized intersections, middle–aged drivers tended to have been going straight, while older drivers were more likely to have been turning left, and were slightly more likely to be turning right and turning right on red (see table below).

• In right–angle collisions at both urban and rural stop–controlled intersections, elderly drivers were more likely than middle– aged drivers to have been starting from a stop.

• In turning collisions, they were more likely to be turning left or right across traffic.

• The examination of the "contributing factors" cited by the officer showed that the middle–aged driver was consistently more likely to have been cited as having exhibited "no improper driving," while the elderly drivers were more likely to have been cited for "failure to yield."

• The crash analyses indicated that both the "young elderly" (ages 65 to 74) and the "old elderly" (age 75 and older) appear to have problems at intersections.
• These problems often involve left–turning maneuvers (at signalized intersections) and turning or "entering" maneuvers at stop– controlled intersections.
• It appears that the problems experienced by elderly drivers involved in crashes either relate to the difficulties in distinguishing target vehicles from surrounding clutter, judging the closing speeds of target vehicles, and/or an inability to use the acceleration capabilities of the cars they are driving.

None

Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 12: A Guide for Reducing Collisions at Signalized Intersections, NCHRP Report 500

National Cooperative Highway
Research Program
Transportation Research Board
500 Fifth Street, N.W.
Washington, DC 20001

COTR:
Not Specified

Antonucci, N.D., Hardy, K.K., Slack, K.L., Pfefer, R., and Neuman, T.R.

2004

133

http://www.trb.org/publications/nchrp/nchrp_rpt_500v12.pdf

Guidelines

Normal

All

This implementation guide provides guidance to highway agencies that want to implement safety improvements at signalized intersections and includes a variety of strategies that may be applicable to particular locations. While the focus of the strategies discussed in this guide is on reducing fatalities at signalized intersections, the implementation of many of these strategies will probably lead to an overall reduction in intersection crashes.

See Methods.

The strategies in this guide were identified from a number of sources, including recent literature, contact with State and local agencies throughout the United States, and Federal programs. Some of the strategies are widely used, while others are used at a State or local level in limited areas. Some have been subjected to well–designed evaluations to prove their effectiveness. On the other hand, it was found that many strategies, including some that are widely used, have not been adequately evaluated.

The implication of the widely varying experience with these strategies, as well as the range of knowledge about their effectiveness, is that the reader should be prepared to exercise caution in many cases before adopting a particular strategy for implementation. To help the reader, the strategies have been classified into three types, each identified by a letter symbol throughout the guide: Proven (P), Tried (T), and Experimental (E).

Guidance for implementation of the American Association of State Highway and Transportation Officials (AASHTO) Strategic Highway Safety Plan (SHSP) is provided. An overview of an 11–step model process for implementing the program of strategies is presented.

Highway Safety, Signalized Intersections, Intersection Crashes, Collision Reduction, Guidelines

Most of the strategies in this guide are low–cost, short–term treatments to improve safety at signalized intersections, consistent with the focus of the entire AASHTO SHSP. For each of these strategies, a detailed discussion of the attributes, effectiveness, and other key factors is presented. Several higher cost, longer term strategies that have been proven effective in improving safety at signalized intersections are also presented, but in less detail. Safety improvement measures include geometric design modifications, changes to traffic control devices, enforcement, and education.

The table below lists the objectives and related strategies for improving safety at signalized intersections.

P = Proven, T = Tried, and E = Experimental

Source: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 12: A Guide for Reducing Collisions at Signalized Intersections, National Cooperative Highway Research Program (NCHRP) Report 500, Transportation Research Board, Washington, DC, 2004, p. V–2. Reprinted with permission.

This report comprises volume 12 of a series of implementation guides addressing the emphasis areas of the AASHTO Strategic Highway Safety Plan, NCHRP Project 17–18(3).

Statistical Models for At–Grade Intersection Accidents,
Addendum (FHWA–RD–99–094)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Joe Bared

Bauer, K.M., and Harwood, D.W.

March 2000

68

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

All

This report is an addendum to the work published in Statistical Models of At–Grade Intersection Accidents (FHWA–RD–96–125) (Bauer and Harwood, 1996). The objective of both research studies was to develop statistical models of the relationship between traffic crashes and highway geometric elements for at–grade intersections.

While the previously published report used only multiple–vehicle crashes in developing predictive models, this addendum presents models based on all collision types (including both multiple–vehicle and single–vehicle crashes).

• The statistical modeling approaches used in the research included lognormal, Poisson, and negative binomial regression analyses. The models for all collision types are similar to those developed in the previous report for multiple–vehicle crashes.
• The analyses include all collision types (i.e., both multiple– and single–vehicle crashes) using 3–year crash frequencies (1990 to 1992) and geometric design, traffic control, and traffic volume data from a database provided by Caltrans (California DOT).
• The data used for the analyses reported in this addendum are in all respects identical to those used for the previous report, except that all collision types were included in the crash frequencies used as the dependent variable in modeling.
• Statistical modeling results for five specific types of intersections are discussed in this report.

Accident Modeling, Traffic Accidents, Geometric Design, At–Grade Intersections, Poisson Regression,Negative Binomial Regression, Lognormal Regression

• The modeling results for crashes if all collision types are combined are similar to those that were found for multiple–vehicle crashes only.
• Geometric design variables accounted for only a small additional portion of the variability.
• Generally, negative binomial regression models were developed to fit the crash data at rural, three– and four–leg, stop– controlled intersections, and at urban, three–leg, stop–controlled intersections.
• Lognormal regression models were found to be more appropriate for modeling crashes at urban, four–leg, stop–controlled intersections, and at urban, four–leg, signalized intersections.
• The lognormal and negative binomial regression models developed to represent the relationships between crashes of all collision types and intersection geometric design, traffic control, and traffic volume variables explained between 16 and 39 percent of the variability in the crash data.
• In all regression models, the major–road average daily traffic (ADT) and crossroad ADT variables accounted for most of the variability in crash data that was explained by the models. Generally, geometric design variables accounted for only a small additional portion of the variability.
• Because of the overdispersion observed in the crash data, the negative binomial distribution was preferred over the Poisson distribution when using a loglinear model.

• The negative binomial and lognormal distributions appear to be better suited to modeling of crash relationships than the normal distribution.
• The form of the statistical distribution selected for modeling any particular type of intersection should be chosen based on a review of the crash frequency distribution for that type of intersection.
• The models do not include the effects for all geometric variables of potential interest to highway designers,and some of the effects they do include are in a direction opposite to that expected. Furthermore, the goodness of fit of the models is not as high as desired. Therefore, the models presented here are appropriate as a guide to future research, but do not appear to be appropriate for direct application in the field.

None

Statistical Models of At–Grade Accidents (FHWA–RD–96–125)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Joe Bared

Bauer, K.M., and Harwood, D.W.

November 1996

157

None

Crash/Demographics Statistical Analysis, Field Test

Normal

All

To develop statistical models of the relationship between traffic crashes and highway geometric elements for at–grade intersections.

Statistical models were developed based on document reviews from a number of sources and results from a pilot field study. The review was limited to multiple–vehicle crash data.

Several major technical tasks were performed during the research, including:

• A review of previously published and unpublished literature and ongoing studies concerning the relationship between traffic crashes and intersection geometrics, as well as between traffic crashes and highway geometric design features in general.
• A review of existing policies, guidelines, standards, and practices for design of at–grade intersections.
• A review of existing highway agency files containing geometric design, traffic control, traffic volume, and crash data, including the databases in the FHWA Highway Safety Information System (HSIS). The Caltrans database was used for developing statistical models and testing statistical approaches.
• Statistical models for the relationships between traffic crashes and geometrics were developed. Alternative modeling approaches were investigated based on various assumptions about the distribution of crashes, including the Poisson, lognormal, negative binomial, and logistic distributions. The goodness of fit of these various alternative models and the role of geometric design variables in those models were assessed. Statistical models were developed for five specific types of intersections.
• A pilot field study to collect data on additional geometric design variables and turning–movement volumes was conducted at a sample of the urban, four–leg, signalized intersections in California. Additional statistical analyses incorporating these field data were conducted.
• A review of hardcopy police accident reports was conducted to further investigate the role of geometric design features in the causation of intersection crashes.

Accident Modeling, Traffic Accidents, Geometric Design, At–Grade Intersections, Poisson Regression, Negative Binomial Regression, Lognormal Regression

• Regression models to determine the relationships between crashes and intersection geometric design, traffic control, and traffic volume variables based on the negative binomial distribution explained between 16 and 38 percent of the variability in the crash data.
• Models developed to predict total multiple–vehicle crashes generally performed slightly better than did models for fatal and injury multiple –vehicle crashes.
• In the modeling of crashes for at–grade intersections, overdispersion was commonly observed and,therefore, the negative binomial distribution was preferred.
• In general, the consideration of major–road ADT and crossroad ADT as separate independent variables provided better modeling results than consideration of a single variable representing either the sum or the product of the two ADT variables.
• In negative binomial regression models for three of five specific intersection types, the major–road ADT and crossroad ADT variables accounted for most of the variability in crash data that was explained by the models. Geometric design variables accounted for a very small additional portion of the variability.
• Addition of field data to the existing data set did not increase the proportion of variation in the crashes that was explained by the lognormal regression models.
• The models do not include the effects of all of the geometric variables of potential interest to highway designers, and some of the effects they do include are in a direction opposite to that expected. Furthermore, the goodness of fit of the models is not as high as desired.

The following conclusions were reached as a result of the statistical analysis of the relationships between traffic crashes and the geometrics of at–grade intersections conducted in this research.

• Traditional multiple linear regression is generally not an appropriate statistical approach to modeling of crash relationships because crashes are discrete, nonnegative events that often do not follow a normal distribution.
• The Poisson, negative binomial, lognormal, and logistic distributions appear to be better suited to modeling of crash relationships than the normal distribution. In all cases, the form of the statistical distribution selected for any particular modeling should be chosen based on a review of the data to be modeled.
• Geometric design features explain relatively little of the variability in intersection crash data for at–grade intersections.
• The models presented here are appropriate as a guide to future research, but do not appear to be appropriate for direct application by practitioners.

An addendum to this report,Statistical Models of At–Grade Intersection Accidents, Addendum(FHWA–RD–99–094), was released in March 2000 and is reviewed separately.

Intersection Collision Avoidance Study, Final Report

Office of Safety
Federal Highway Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:
Not Specified

Bellomo–McGee, Inc.

September 2003

79

None

Literature Review, Field Test

Normal

Not Specified

To define and evaluate infrastructure–only Intersection Collision Avoidance System (ICAS) concepts aimed at reducing the number of intersection crashes.

System engineering analyses were performed to define and evaluate the feasibility and effectiveness of alternative infrastructure–based advanced technology concepts. These included development of functional requirements and conceptual designs, and the testing of the feasibility of those designs at high–crash intersections in three States.

Literature Review:

• This included a review of crash studies, human factors work related to crash avoidance, and current advanced technology intersection safety countermeasures. Included in the literature review was an examination of technology, sensors, and displays capabilities.

Crash Analysis:

• Crashes were analyzed at selected sites within the Infrastructure Consortium (IC) States: Minnesota, California, and Virginia.
  • Each IC member State identified 20 high–incident intersections for review and analysis.
  • Police reports for 3 years of crashes provided a large database for analysis of crossing–path crashes. This database was used to determine primary crash types and causal factors.
  • A final step of this task was to select two sites from each State that would be candidates for implementing advanced intelligent countermeasures.

Define and Evaluate ICAS Concepts:

• This task included developing several concepts for reducing crossing–path crashes using intelligent vehicle systems and sensors, communication displays, etc.

Feasibility Testing at the Six Candidate Intersections:

• This was performed by collecting field data and applying it to the requirements of the particular concepts.

Intersection, Collision Avoidance, Infrastructure, Intersection Collision Avoidance System

• The project identified certain parameters required for characterizing traffic flow based on current Intelligent Transportation Systems (ITS) applications/concepts for traffic management.
• Information on human factors issues important to the selection and design of infrastructure–based technology was identified. These included driver age, vehicle gap acceptance, and response to emergency events.
• The three successive years of data showed that Left Turn Across Path of Opposite Direction (LTAP/OD), Straight Crossing Path (SCP), and Left Turn Across Path of Lateral Direction (LTAP/LD) crashes were the most frequent types of crash, regardless of whether or not the intersection was signalized.
• Crashes involving signal violation were mostly a result of not seeing the signal or its indication, or trying to "beat" the amber signal.
• Inability to judge available gaps in traffic and not seeing right–of–way vehicle were the main causal factors for crashes that did not involve signal violation.
• Based on the analyses of crashes and casual factors, six intersection collision avoidance concepts were developed. Four of the concepts involve timely communication of information to at–risk motorists, while the remaining two preempt the normal signal operation to prevent a crash.
• Feasibility analysis data showed that at all of the six candidate intersections, the suggested concept was feasible, based on the vehicle data collected at the site.
• The result of the cost–benefit analysis indicated that five of the six candidate intersections showed the potential to quickly recoup the expenses of design and installation of the suggested infrastructure–based collision countermeasure.

• Based on this work, it was determined that implementing an ICAS to address each of the three most prevalent types of intersection crashes was feasible. In addition, the cost–benefit analysis showed a quick recouping of ICAS implementation costs.
• Motorist response to roadside communication devices still requires extensive testing, as this is a critical requirement of several concepts.
• Recommended further studies pertain to increased onsite data collection to validate preliminary findings and human factors testing to meet the functional requirements of the operational concepts. Human factors testing consists of the evaluation of communications modes to inform and warn motorists.

None

Driver Understanding of Protected and Permitted Left–Turn Signal Displays

(Transportation Research Record 1464, pp. 42–50)

Civil Engineering Department
University of Nebraska–Lincoln
Lincoln, NE 68588–0531

COTR:
Not Specified

Bonneson, J.A., and McCoy, P.T.

1994

9

None

Survey

Normal

Not Specified

To determine if some protected and permitted left turn (PPLT) signal designs cause more confusion and operational and safety problems for drivers than others.

Driver comprehension of PPLT signal designs was evaluated by conducting a survey of 1,610 drivers. The survey included a perspective view of an intersection approach and its traffic signal display, followed by multiple–choice questions about the correct driving action.

Survey Questionnaire:

• On each survey, one perspective view of an intersection approach was shown at the top of the page and two multiple–choice questions asked the correct identification of a particular indication type.
• The survey questions focused on the following four display indications in six different PPLT designs:
  • Permitted left turn: Green ball for both the left turn and through movements.
  • Protected left turn only: Left–turn green arrow and through red ball, consistent with the Manual on Uniform Traffic Control Devices (MUTCD) specifications.
  • Overlapped left turn and through: Left–turn green arrow and through green ball.
  • Protected/Modified left turn only: Displayed only the green arrow in the PPLT signal head without the red ball.
• The six PPLT designs varied in terms of the location of the signal head with respect to the lane line, the arrangement of the lenses in the s ignal head, and the inclusion of an auxiliary sign.

Distribution Method:

• Survey was administered in three of Nebraska’s largest cities: Omaha, Lincoln, and Grand Island.
• Survey was administered in person at the local department of motor vehicles in each city.

Protected and Permitted Left Turn, Signal Design, Intersection Safety

Survey Demographics:

• Only 70 percent of the survey respondents correctly understood the meaning of the PPLT signal design.
• There was a trend toward a decreased understanding of the PPLT designs with increased age and driving experience.
• There was also a trend toward better understanding with more education.

Design Comparisons:

• The results indicated that drivers appear to have the best understanding of the exclusive vertical PPLT design. The difference in the results for this design and the least understood design is about 8 percent (see table).
• None of the differences between each design is significantly different. Although the differences suggest that some designs are better understood, a larger number of responses would be needed to confirm these trends.
• With regard to differences in understanding the various indications, the results indicate that the overlap indication is least understood (only about one–half of the drivers surveyed answered this question correctly).

Signal–Head Location and Sign Use:

• The exclusive head location increased driver understanding by about 4 to 5 percent over the shared head location.
• The results indicated that designs with a sign decrease driver understanding by about 6.5 percent. It was found that the use of a sign tends to confuse more drivers during the overlap and protected phases than it helps during the permitted phase.

From Transportation Research Record 1464, Transportation Research Board, National Research Council, Washington, DC, 1994,
table 2, p. 48. Reprinted with permission.

• The survey results indicated that the exclusive vertical PPLT design is correctly understood by the highest proportion of drivers.
• Of the three indications considered, the overlap indication is understood by the smallest number of respondents.
• The survey results indicate that drivers are better able to understand PPLT designs with any of the following characteristics: Modified protected indication, PPLT head centered over the opposing left–turn lane, and no auxiliary sign.

None

Review and Evaluation of Factors That Affect the Frequency of
Red–Light Running (FHWA/TX–02/4027–1)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Not Specified

Bonneson, J., Brewer, M., and Zimmerman, K.

September 2001

78

None

Literature Review, Crash/Demographic Statistical Analysis

Normal

Not Specified

To describe how traffic engineering countermeasures can be used to minimize the frequency of red–light running (RLR) and associated crashes at intersections.

This report describes the findings from the first year of a 2–year project. During the first year, studies were conducted on RLR frequency and crash rates at 12 intersection approaches in 3 Texas cities.

Field Data Collection:

• The field study at each site included the collection of a wide range of geometric, traffic flow, traffic control, and operational characteristics.
• These data were collected using a variety of methods, including video recorders, laser speed guns, and site surveys.

Safety Data Collection:

• The safety data collection activity consisted of the acquisition of historical crash records for each intersection included in the field studies.
• To facilitate the analysis, computerized databases were requested from the Texas Department of Public Safety and the appropriate city agencies.
• The request was for the most recent 36 months for which complete information was available and for all four approaches to each intersection. These data were used to quantify the relationship between RLR and crash frequency.

Signalized Intersection, Change Interval, Signal Timing Design, Dilemma Zone

• A review of the literature revealed that the following are influential factors in the RLR process: (1) flow rate on the subject approach, (2) number of signal cycles, (3) phase termination by max–out, (4) probability of stopping, (5) yellow interval duration, (6) all–red interval duration, (7) entry time of the conflicting driver, and (8) flow rate on the conflicting approach.
• A review of the literature also indicated that drivers are less likely to stop when they: (1) have a short travel time to the intersection, (2) have higher speeds, (3) are traveling in platoons, (4) are on steep downgrades,(5) are faced with relatively long yellow indications, and (6) are being closely followed.
• The duration of the yellow interval is generally recognized as a key factor that affects the frequency of RLR. Researchers suggest that the yellow interval should be based on the travel time of the 85^th (or 90^th) percentile driver. The corresponding yellow interval duration should range from 4.0 to 5.5 seconds (s) (with larger values appropriate for higher speed approaches).
• The countermeasures with the greatest potential to reduce RLR (as determined from the literature review) are listed in the table below.

¹Bolded countermeasures were selected for evaluation in this project.

• Analysis of approach volume on RLR frequency revealed that RLR frequency was highly correlated with the flow rate at the end of the phase. Other factors found to be correlated with the frequency of RLR include yellow interval duration and the percentage of heavy vehicles.
• Yellow intervals of less than 3.5 s appear to be associated with a significant number of RLR events per hour.
• The findings from these studies indicate that the frequency of RLR increases in a predictable way with increasing approach volume, increasing heavy–vehicle percentage, and shorter yellow interval durations.
• Crash data analyses indicate that right–angle crashes increase exponentially with an increasing frequency of RLR.
• Models for computing an intersection approach’s RLR frequency and related crash rate are described.

None

Engineering Countermeasures to Reduce Red–Light Running
(FHWA/TX–03/4027–2)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Not Specified

Bonneson, J., Zimmerman, K., and Brewer, M.

August 2002

122

None

Field Test

Normal

Not Specified

To describe how engineering countermeasures can be used to minimize the frequency of red–light running (RLR) and associated crashes.

This report describes the factors that are associated with RLR, as well as several countermeasures that have been used to reduce its frequency. Initially, there is an examination of the RLR process in terms of the events necessary to precipitate an RLR event. Then, various engineering countermeasures are identified. Next, a before/after study is described.

Field Study:

• During the first year, engineering countermeasures were identified and implemented at 10 intersections in 5 Texas cities.
• Before/after studies of RLR frequency were then conducted at two sites (i.e., approaches) at each of the 10 intersections.
• One or more of the five countermeasures identified were implemented at most of the sites.
• Data collection consisted of a wide range of geometric, traffic flow, traffic control, and operational characteristics.
• The data were collected using a variety of methods, including video recorders, laser speed guns, and site surveys.

Crash Data Analysis:

• The 3–year crash history for each intersection was compared to its observed frequency of RLR.
• Computerized databases were requested from the Texas Department of Public Safety and the appropriate city agencies.

Signalized Intersections, Change Interval, Yellow Interval, Red–Light Running

• Factors that lead to conflict: The following factors are related to the occurrence of RLR: (1) flow rate on the subject approach, (2) number of signal cycles, (3) phase termination by max–out, (4) probability of stopping, and (5) yellow interval duration.
• The results of the field study indicate that more than 10,018 signal cycles were observed at 20 intersection approaches. During these cycles, 586 vehicles entered the intersection (as defined by the stop line) after the change in signal indication from yellow to red. Of the 586 vehicles, 84 were heavy vehicles and 502 were passenger cars. Overall, 0.86 percent of heavy vehicles violated a red indication and 0.38 percent of passenger cars violated the red indication.
• The overall average RLR rates are 4.1 red–light runners per 1,000 vehicles and 1.0 red–light runners per 10,000 vehicle cycles.
• The following countermeasures were implemented at the intersection approaches, with the corresponding percent reduction in parentheses (the only countermeasure found to be statistically significant was the yellow interval duration increase):
  • Add light–emitting diode (LED) lighting to the yellow indication (49 percent reduction).
  • Increase the yellow interval duration (70 percent reduction).
  • Add backplates and increase yellow interval duration (18 percent reduction).
  • Increase cycle length and improve signal operation (uncertain effect).
  • Improve progression and increase cycle length (uncertain effect).
  • Add backplates and add LED lighting to the yellow indications (35 percent reduction).

• The typical intersection approach experiences from 3.0 to 5.0 red–light runners per 1,000 vehicles and 1.0 red–light runners per 10,000 vehicle cycles. An intersection with an RLR rate that is greater than that of the typical intersection should be the primary target of a treatment program.
• A heavy–vehicle operator is twice as likely to run the red indication as is a passenger car driver.
• RLR is more frequent at intersections with platoons arriving near the end of the green indication. Engineers developing signal coordination plans should avoid having platoons arrive near the end of the signal phase. If this situation cannot be avoided, then a longer cycle length should be used.
• About 80 percent of drivers that run red lights enter the intersection within 1.0 s after the end of the yellow cycle. Hence, engineering countermeasures focused on driver recognition of, and response to, the yellow indication are likely to be the most cost–effective.
• In addition to an increase in yellow interval duration, several other engineering countermeasures were identified as having the potential to reduce RLR. Specifically, it was found that the use of backplates would reduce RLR by 25 percent, a 20–s increase in cycle length would reduce RLR by 18 percent, and the use of yellow LEDs may reduce RLR by 13 percent.
• The findings indicate that the frequency of RLR decreases in a predictable way with decreasing approach flow rate, longer clearance path lengths, longer headways, and longer yellow interval durations.
• The crash data analyses indicate that right–angle crashes increase exponentially with an increasing frequency of RLR.

None

Analysis of Fatal Crashes Due to Signal and Stop Sign
Violations (DOT–HS–809–779)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:
Not Specified

Campbell, B.N., Smith, J.D., and Najm, W.G.

September 2004

159

http://www-nrd.nhtsa.dot.gov/departments/nrd-12/pubs_rev.html

Crash/Demographic Statistical Analysis

Normal

Light Vehicles

This research supports the National Highway Traffic Safety Administration (NHTSA) in developing performance specifications for stop sign/traffic signal violations and insufficient gap warning systems (e.g., left turn across path).

Crash data for the analysis were obtained from the 1999–2000 Fatality Analysis Reporting System (FARS) crash databases. This report identified the crash scenarios, described the crash contributing factors, and characterized the infrastructure where fatal crashes occurred in 1999 and 2000.

• The analysis began with all 1999 and 2000 fatal crashes and then segregated the crashes by the type of traffic control device at the crash site.
• These crashes were then examined to determine whether the driver violated the traffic signal or stop sign and what type of violation occurred.
• Traffic control device violations were classified into two categories: (1) failure to obey and (2) failure to yield.
• Fatal crashes involving light vehicles that violated the traffic signal or stop sign were separated into single–vehicle, two–vehicle, and multiple–vehicle crash categories.

Light Vehicles, Crashes, Contributing Factors, Intelligent Vehicle Initiative, Fatal Crashes, Traffic Signals, Stop Signs, Violations, Precrash

• A total of 9,951 vehicles were involved in fatal crashes at traffic signals in 1999 and 2000—20 percent of these vehicles failed to obey the signal and 13 percent failed to yield the right of way.
• For crashes at stop signs, 13,627 vehicles were involved in fatal crashes —21 percent failed to obey the sign and 23 percent failed to yield the right of way.
• Single–vehicle crashes accounted for 8 percent and 6 percent, two–vehicle crashes accounted for 75 percent and 87 percent, and multiple–vehicle crashes accounted for 18 percent and 7 percent of all light–vehicle violation fatal crashes at traffic signals and stop signs, respectively.
• About 64 percent and 95 percent, respectively, of the "failure to obey" and "failure to yield" single–vehicle crashes at traffic signals were pedestrian crashes. On the other hand, 76 percent of the "failure to yield" crashes at stop signs were pedestrian crashes, while 95 percent of the "failure to obey" crashes at stop signs were other crashes such as run–off–road crashes.
• Single–vehicle traffic signal crashes primarily occurred in urban areas (91 percent), whereas 57 percent of stop sign crashes occurred in rural areas. Most single–vehicle crashes occurred on two–lane roadways regardless of the type of violation.
• Approximately 65 percent and 12 percent, respectively, of the "failure to obey" and "failure to yield" two–vehicle crashes were straight crossing–path crashes and, in contrast, 29 percent and 81 percent, respectively, were left crossing–path crashes.
• Straight crossing–path crashes were 2.24 times more likely than left–turn crossing–path crashes for "failure to obey" violations. In contrast, left–turn crossing–path crashes were 6.55 times more likely than straight crossin–gpath crashes for "failure to yield" right–of–way violations.
• In 1999 and 2000, there were 889 fatal multiple–vehicle crashes that involved violations by light vehicles. About 58 percent occurred at traffic signals, while the remaining 42 percent occurred at stop signs. At traffic signals, drivers failed to obey the signal in 67 percent of the crashes and failed to yield the right of way in the remaining 33 percent of the crashes.
• About 82 percent of multiple–vehicle fatal crashes at traffic signals occurred on urban roadways. Conversely, about 57 percent of multiple–vehicle fatal crashes at stop signs occurred on rural roadways.
• The majority (80 percent) of stop sign crashes occurred on two–lane roadways. On the other hand, half of the traffic signal crashes (50 percent) occurred on two–lane roadways.
• Alcohol was involved in 37 percent of all single–vehicle fatal crashes involving a light vehicle violating the traffic signal or the stop sign.
• Single–vehicle crashes had the highest rate of speeding and inattention, 33 percent and 14 percent, respectively.
• Inattention or distraction was reported for about 11.0 percent of all light–vehicle violations in two–vehicle fatal crossing–path crashes.
• Alcohol was linked to 14 percent of all light–vehicle violations in two–vehicle fatal crossing–path crashes.
• Speeding or racing, including police chase, was related to 10 percent of all light–vehicle violations in multiple–vehicle fatal crashes. This factor was four times more prevalent in traffic signal crashes than in stop sign crashes.
• Inattention or distraction was the second most reported factor, representing about 7 percent of all light–vehicle violations in multiple–vehicle fatal crashes.
• Alcohol was linked to 13 percent of all light–vehicle violations in multiple–vehicle crashes.

• No major differences were found among the crash categories regarding the infrastructure where these fatal crashes occurred.
• The authors concluded that fatal crashes involving a light vehicle violating the traffic signal or stop sign occur in similar locations, regardless of whether they are single–vehicle, two–vehicle, or multiple–vehicle crashes.
• Alcohol, speeding, and inattention are the three most common contributing factors for fatal crashes at traffic signals and stop signs.

None

Examination of Intersection, Left Turn Across Path Crashes and
Potential IVHS Countermeasures (DOT–HS–808–154)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:
Not Specified

Chovan, J.D., Tijerina, L., Everson, J.H., Pierowicz, J.A., and Hendricks, D.L.

September 1994

52

http://www.its.dot.gov/itsweb/EDL_webpages/webpages/SearchPages/Alpha_Search.cfm

Crash/Demographic Statistical Analysis

Imminent Crash (Intersection Collision Avoidance (ICA))

Light Vehicles

To provide a preliminary analysis of intersection–related, left turn across path (LTAP) crashes and applicable countermeasure concepts for the Intelligent Vehicle–Highway System (IVHS) program. The intent of the report is to increase understanding of the crash avoidance requirements associated with LTAP crashes.

• This report presents the results of a study of the intersection, LTAP type of collision as identified by the NHTSA Office of Crash Avoidance Research (OCAR).
• A total of 154 LTAP crashes selected from the 1992 Crashworthiness Data System (CDS) were analyzed and weighted for severity so that they might more closely approximate the national profile.

• A framework for IVHS crash avoidance concepts regarding LTAP crashes is presented.
• A simple LTAP model is presented in which driver warnings are analyzed in terms of principal other vehicle (POV) time headway. This model incorporates the above framework and is divided into two subtypes based on whether the subject vehicle (SV) comes to a complete stop before entering the intersection.
• Two types of LTAP crashes were identified:
  • Subtype 1, where the SV slows, but does not stop; begins the left turn; and strikes or is struck by the oncoming POV.
  • Subtype 2, where the SV stops, then proceeds with the left turn, and strikes or is struck by the POV.
• The report concludes with a discussion of research needs to support further refinement of the LTAP scenario and other crash avoidance concepts.

Vehicle Crash Analysis, Crash Countermeasures, Intelligent Vehicle–Highway System, Kinematic Models, Crash Circumstances

Causal Factors and Crash Characteristics:

• At both signalized and unsignalized intersections, the LTAP crashes occurred for the following reasons:
  • SV driver was unaware of the crash hazard.
  • SV driver misjudged how fast the POV was approaching.
  • SV driver misjudged how close the POV was to their intersection.
  • Potentially harmful situation was not obvious to the SV driver.
  • SV driver’s view was obstructed.
• SV was more likely to be struck by another vehicle than to strike another vehicle.
• Most LTAP crashes occurred on roadways with posted speed limits of 56 kilometers per hour (km/h) (35 miles per hour (mi/h)) or greater, on dry pavement (80 percent), and under no adverse weather conditions (86 percent).

IVHS Crash Avoidance Concepts for LTAP Crashes:

• A framework for IVHS crash avoidance concepts was presented based on a series of sequential countermeasure steps as follows (see figure A):
  • Driver alerts.
  • Higher intensity driver warnings.
  • Partially automated control crash avoidance maneuvers.
  • Fully automated control maneuvers.

Research Needs:

• Clinical analysis area: Cross–tabulation of causal analysis between subtypes, concordance of parallel analyses,analysis of cases caused by a loss of traction.
• Driver behavior at left turns across path: Higher order responses, correlations, driver decision processes,maximum turn velocities, control intervention, interaction between drivers, alternative alert displays, transition from preplanned to emergency maneuvers, driver acceptance of LTAP collision avoidance systems (CAS), headway time prediction, driver reaction time.
• LTAP algorithm research needs: Additional CAS concepts, CAS set points, impact of acceleration profiles on robustness, false alarms, warning familiarity, evasive maneuvers, POV turning.
• Further modeling research needs: Multiple–vehicle interactions, inclusion of variables, speed profiles, indicators of intent, normal driving behavior.

None

Examination of Unsignalized Intersection, Straight Crossing–
Path Crashes, and Potential IVHS Countermeasures
(DOT–HS–808–152)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:
Not Specified

Chovan, J.D., Tijerina, L., Pierowicz, J.A., and Hendricks, D.L

August 1994

72

http://www.its.dot.gov/itsweb/EDL_webpages/webpages/SearchPages/Alpha_Search.cfm

Crash/Demographic Statistical Analysis

Imminent Crash (ICA)

Light Vehicles

To provide a preliminary analysis of unsignalized intersection, straight crossing path (UI/SCP) crashes and applicable countermeasure concepts for the IVHS program. The intent of the report is to increase the understanding of crash avoidance requirements associated with UI/SCP crashes.

• This report presents the results of a study of the UI/SCP type of collision as identified by the NHTSA Office of Crash Avoidance Research (OCAR).
• 100 UI/SCP crashes selected from the 1992 Crashworthiness Data System (CDS) were analyzed and weighted for severity so that they might more closely approximate the national profile.

• An analytic model of intersection negotiation behavior at unsignalized intersections was presented to indicate possible sources of driver actions that might contribute to such crashes.
• Two types of UI/SCP crashes were identified as follows:
  • Subtype 1, where the SV ran the stop sign.
  • Subtype 2, where the SV stopped, then proceeded against cross traffic.
• The two crash subtypes were examined for the following characteristics: Speed distribution, POV travel direction, SV’s role in the crash event.
• Crash avoidance concepts regarding UI/SCP crashes were discussed, and partially automatic control systems and fully automatic control systems were presented as control intervention schemes.
• The report concluded with a discussion of research needs to support further refinement of the UI/SCP scenario and other crash avoidance concepts.

Vehicle Crash Analysis, Crash Countermeasures, IVHS, Kinematic Models, Crash Circumstances

Crash Causal Factors:

• UI/SCP crashes occurred for the following reasons:
  • Driver unawareness caused by inattention, failure to see, and obstructed vision.
  • Driver misjudgment of POV velocity/gap.
  • Deliberate violation of sign.

Crash Countermeasure Concepts:

IVHS crash countermeasure concepts, specific to UI/SCP crash subtypes, were devised in three different categories to address the major causal factors as follows (see figure A):

• In–vehicle alert: Subtype 1—Intersection detection alert, Subtype 2—In–vehicle display of approaching POV.
• Driver warning: Subtype 1—Graded warnings to SV driver, Subtype 2—Gap acceptance aid that warns the SV when it is unsafe to enter the intersection.
• Control intervention: Both subtypes—CAS–controlled soft braking, moderate braking, or graded braking with or without driver override (see figure B).

Research Needs:

• Clinical analysis area: Increase sample size in analysis, concordance of parallel analysis.
• Driver behavior at unsignalized intersections: Higher order responses, correlations, drivers’ decision processes, control intervention, interaction between drivers, alternative alert displays.
• UI/SCP algorithm research needs: Additional CAS concepts, error modeling of algorithm data, CAS set points, impact of velocity profiles on algorithm robustness.
• Further modeling research needs: Multiple–vehicle interactions.

None

Safety Impact of Permitting Right–Turn–on–Red: A Report to Congress by the National Highway Traffic Safety Administration (DOT–HS–808–200)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:
Not Specified

Compton, R.P., and Milton, E.V.

December 1994

47

None

Literature Review, Crash/Demographic Statistical Analysis

Normal

Not Specified

To provide a brief summary of State laws and the safety impacts of permitting right and left turns at red lights.

This report presents a brief summary of the current status of State implementation of laws permitting right and left turns at red lights, a brief review of previous research, and the results of analyses of currently available data assessing the safety impact of permitting a right turn on red (RTOR).

Two sources of data were used in completing this report:

• Fatality Analysis Reporting System (FARS): FARS includes a code for an RTOR vehicle maneuver. However, FARS does not include information on whether a vehicle was turning right on red at the time of the crash, only that the vehicle was turning right at the time of the crash at an intersection where RTOR is permitted.
• Data from four State crash data files (Illinois, Indiana, Maryland, and Missouri): The four State files include on their crash report form either a code for an RTOR vehicle maneuver or other codes that make it possible to determine that an RTOR maneuver was executed. With one exception, data used in the analysis cover the years from 1989 through 1992. From Illinois, only 1989 through 1991 data were available.

Right Turn on Red (RTOR), Left Turn on Red (LTOR), Safety Impact, Intersection Crashes

Analysis of FARS data showed the following:

• Approximately 84 fatal crashes occurred per year during the time period involving a right–turning vehicle at an intersection where RTOR is permitted.
• During this same time period, there were 485,104 fatalities. Thus, less than 0.2 percent of all fatalities involved a right–turning vehicle maneuver at an intersection where RTOR is permitted. FARS, however, does not discern whether the traffic signal indication was red. Therefore, the actual number of fatal RTOR crashes is somewhere between zero and 84 and may be closer to zero.
• Slightly less than half of the fatal RTOR crashes involve a pedestrian (44 percent); 10 percent a bicyclist; and, in 33 percent of the crashes, one vehicle striking another vehicle (see figure).

The results of the data analysis from the four State crash files suggest the following:

• RTOR crashes represent a very small proportion of the total number of traffic crashes in the four States (0.05 percent).
• RTOR injury and fatal crashes represent a fraction of 1 percent of all fatal and injury crashes (0.06 percent).
• RTOR crashes represent a very small proportion of signalized intersection crashes (0.4 percent).
• When an RTOR crash occurs, a pedestrian or bicyclist is frequently involved. For all States, for all years of the studies, the proportion of RTOR pedestrian or bicyclist crashes to all RTOR crashes was 22 percent.
• RTOR pedestrian and bicyclist crashes usually involve injury. Some 93 percent of RTOR pedestrian or bicyclist crashes resulted in injury.
• Only 1 percent of RTOR pedestrian and bicyclist crashes resulted in fatal injury. However, less than 1 percent of all fatal pedestrian and bicyclist crashes result from RTOR vehicle maneuvers.
• Most RTOR crashes occur between 6:00 a.m. and 6:00 p.m.

• A relatively small number of deaths and injuries each year are caused by RTOR crashes.
• These represent a very small percentage of all crashes, deaths, and injuries.
• Because the number of crashes resulting from RTOR is small, the impact on traffic safety has also been small.
• Insufficient data exist to analyze LTOR.

None

Safety Evaluation of Red–Light Cameras
(FHWA–HRT–05–048)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Michael Griffith

Council, F.M., Persaud, B., Eccles, K., Lyon, C., and Griffith, M.S.

April 2005

8

http://www.tfhrc.gov/safety/pubs.htm

Field Test

Normal

Not Specified

To determine the effectiveness of red–light camera (RLC) systems in reducing crashes.

The study involved Empirical Bayes (EB) before/after research using data from seven jurisdictions across the United States to estimate the crash and associated economic effects of RLC systems. The study included 132 treatment sites and specially derived rear –end and right–angle unit crash costs for various severity levels.

• The choice of jurisdictions to be included in the study was based on an analysis of sample size needs and the data available in potential jurisdictions.
• The jurisdictions chosen were: El Cajon, San Diego, and San Francisco, CA; Howard County, Montgomery County, and Baltimore, MD; and Charlotte, NC.
• Data were required not only for RLC–equipped intersections, but also for a reference group of signalized intersections that were not equipped with RLCs, but were similar to the RLC locations.

Red–Light Camera, Empirical Bayes, Crash Evaluation, Economic Analysis, Signalized Intersection

• There was a significant decrease in right–angle crashes, but there was also a significant increase in rear–end crashes (see table A).
• The economic estimates, with property damage only (PDO) crashes excluded, show a positive aggregate economic benefit of more than $18.5 million over approximately 370 site–years, which translates into a crash–reduction benefit of approximately $50,000 per site–year (see table B).

Note: A negative number indicates a decrease.

Note: A negative number indicates a decrease.

• Crash effects detected were consistent in direction with those found in many previous studies (a decrease in right–angle crashes and an increased in rear–end crashes).
• There was a modest aggregate crash cost benefit of RLC systems.
• A disaggregate analysis found that the greatest economic benefits are associated with factors of the highest total entering annual average daily traffic (AADT), the largest ratios of right–angle to rear–end crashes, and the presence of protected left–turn phases.
• There were weak indications of a spillover effect that point to a need for a more definitive, perhaps prospective, study of this issue.

None

Red Light Violations and Crashes at Urban Intersections

(Transportation Research Record 1734, pp. 52–58)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Not Specified

Datta, T.K., Schattler, K., and Datta, S.

2000

7

None

Field Test

Normal

Not Specified

To determine if any difference existed between red–light violation characteristics among intersections with properly designed clearance intervals and intersections that did not have appropriate yellow change intervals and, more importantly, an all–red interval.

A study was performed in Detroit, MI, to compare the red–light violation characteristics of intersections with properly designed all–red intervals and those intersections without all–red intervals. In the absence of "before" violation data, a comparative parallel experimental study was used. An evaluation of before/after crash frequencies was also performed to determine the effectiveness of implemented improvements on right–angle crashes and injuries.

• Five signalized intersection sites in Detroit were studied: Three treatment (test) intersections, two intersections in the same area were selected as control sites.
  • Treatment sites: All treatment intersections had clearance intervals (yellow and all–red intervals) that were calculated based on site–specific criteria such as approach speed, vehicle deceleration rates for stopping, and intersection geometry.
  • Control sites: These sites had a yellow interval only.
• Red–light violations were monitored through a series of onsite field observations. A total of 16 h of field data were collected at each of the five sites during off–peak periods.
• Trained field personnel observed all traffic movement through each intersection and recorded the frequency of red–light violations based on the directional movement of travel.

Red–Light Violations, Intersection Safety, Yellow Change Intervals

• In performing the effectiveness evaluation, after–improvement crashes were compared with the 3–year averages of crash data for the same months of the "before" period.
• The results show a significant reduction in red–light violation rates for the treatment sites. The average red–light violations per hour for the treatment sites was 3.6, while the control sites had an average of 8.08.
• The before/after comparison of right–angle, injury, and total crashes at all three treatment sites shows that the crash frequencies were significantly lower after the treatment (see tables below).

^aRepresents an annual average of 24–month data (June 1997 to May 1999).

^aRepresents an annual average of 21–month data (June 1997 to May 1999).

^aRepresents an annual average of 29–month data (June 1997 to May 1999).

From Transportation Research Record 1734, Transportation Research Board, National Research Council, Washington, DC, 2000, table 3, p. 57. Reprinted with permission.

• Analysis indicated significantly lower red–light violations at the treatment sites.
• Analysis also indicated an extraordinary reduction in right–angle and injury crashes.
• Study demonstrated that substantial benefits, in terms of reducing red–light violations and right–angle crashes, can be achieved by introducing a well–designed, all–red interval.

None

Guidance for Using Red Light Cameras

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

COTR:
Not Specified

Federal Highway Administration and National Highway Traffic
Safety Administration.

March 2003

60

http://www.tfhrc.gov/safety/intersect.htm

Guidelines

Normal

Not Specified

The guidance in this report is intended to provide critical information for State and local agencies on relevant aspects of red–light camera (RLC) systems in order to promote consistency and proper implementation and operation.

FHWA and NHTSA have developed this guidance for the use of State and local agencies on the implementation and operation of RLC systems. This guidance can be used by State and local agency managers, transportation engineers, and law enforcement officials to identify and properly address safety problems resulting from red–light running (RLR) within their jurisdiction.

The document is divided into the following sections:

• Understanding of the problem.
• Problem identification.
• Countermeasures and their applications.
• RLC program implementation.

Red–Light Running, Red–Light Cameras, Intersections

• An engineering study may identify the following conditions that may be present at a signalized intersection and contribute to RLR by motorists: Grade, poor visibility, temporary roadside obstructions, line of sight, sign reflectivity, traffic volumes, signal timing, and weather.

Problem Identification:

• The following steps are recommended for investigating intersection safety: Data collection; RLR violation data; intersection crash data; driver behavior observations; traffic–, signal–, and intersection–related data; and motorist complaints and comments.

Countermeasures and Their Applications:

• Engineering countermeasure solutions to be considered include: Modifying traffic signal timing, improving signage and marking, improving sight lines, modifying grades and/or grade separation, adjusting the prevailing speeds, changes in surface treatments, altering lane configurations, and replacing the traffic signal with some other form of traffic control device or intersection type.
• Education: A well–designed public information and education campaign should provide information and data that explain what RLR is, why RLR is dangerous, and what actions are currently being undertaken to reduce the incidence of RLR.
• Enforcement by law enforcement officers: Officers in patrol cars or using motorcycles can be a cost–effective solution to reduce RLR at problem intersections. However, unless an observer and a stopping team are used, officers also must pass through the intersection on a red signal indication.
• Red–light cameras: If engineering, educational, and traditional enforcement countermeasures are proven to be unsuccessful, RLR camera technologies, if authorized by law, may be considered.

RLC Program Implementation:

• Early planning and startup: The following are the key elements required for the early planning and startup of an RLC program.
  • Establishment of an oversight committee: This should be inclusive of all stakeholders (engineers, educators, law enforcement, prosecutors, judges, and, most importantly, private citizens).
  • Establishment of program objectives: The oversight committee should define, as clearly as possible, the RLC program objectives as an early step for moving forward. Program objectives should address specific operational needs.
  • Identification of the legal requirements: In particular, concerns and issues related to privacy, citation distribution, and types of penalties need to be thoroughly addressed and resolved prior to the startup of an RLC program.
• Engineering design of RLC systems: Plans should address the placement of the RLC system equipment and related components, including camera equipment, supporting structure, intersection lighting, vehicle detection system, communications, pull boxes and conductor schedule, electrical service, and warning signs.

See Key Results above.

None

Intersection Angles and the Driver’s Field of View

Arkansas State Highway and
Transportation Department
P.O. Box 2261
Little Rock, AR 72203
COTR:

Not Specified

Gattis, J.L., and Low, S.T.

November 1997

37

None

Field Test

Normal

Various Types

To identify the constraints on the angle of a left-skewed intersection, as affected by the vehicle body limiting a driver’s line of sight to the right.

In this research project, the angles at which drivers’ lines of sight were obstructed by the body of their vehicles were measured. Two driver positions ("sit back" and "lean forward") were used. A 13.5-degree vision angle was selected to represent an intermediate position (between the "sit back" and the "lean forward" positions).

Design Vehicle:

• The following vehicle design types were located and arrangements were made to allow measurements to be taken: Ambulance, dump truck, motor home, school bus, small bus on a van chassis, single-unit truck mounted with container, and truck tractor (cab of an 18–wheeler).

Driver Position:

• "Sit back" position: Driver was in a fully leaned-back position, with his/her back touching the seatback. In this position, the driver relies mainly on head and neck movement to get the maximum viewing angle to his/her right. This position permits the driver to remain comfortably seated against the seatback.
• "Lean forward" position: Driver leaned forward so that the driver’s eyes were over the juncture where the steering wheel is attached to the column. In addition to using head and neck movements, the driver leaned his/her upper body far forward to get a greater viewing angle to the right. In such a position, the driveer’s chest was often pressing the driver’s arms against the steering wheel, thus confining the movement of the driver’s arms.

Field Measurements:

• The lengths of both the front and rear axles were measured. The difference between these two widths was divided by two. This "half of the width" difference was added to the front axle width and this dimension was marked on the parking lot surface to the outside of the right-front tire. The "right-edge parallel line" was determined by connecting a line from this point to the edge of the right-rear tire.
• Next, the researchers constructed a perpendicular line projecting from the driver’s eyes with the driver in the "sit back" position and another perpendicular line projecting from the "lean forward" position.
• A surveying range pole with an attached level was placed on the right-offset line, within the seated driver’s field of view. As it was slowly moved backward, the person in the driver’s seat signaled when a vehicle body obstruc tion caused him/her to lose sight of the pole. This position was marked. This procedure was performed three times for each position.

Intersection Angle, Sight Distance, Geometric Design

Effects on Sight Distance at Intersections:

• With a 5.4-meter (m) (17.7-foot (ft)) setback and the driver in the intermediate "lean forward" position, the resulting available sight distances for 60, 65, 70, and 75 degrees were found to be 40, 55, 96, and 408 m (131, 180, 315, 1339 ft), respectively (see table A).
• The currently recommended minimum intersection angle, 60 degrees, has a resulting available sight distance equal to the stopping sight distance (SSD) for 37-km/h (23-mi/h) travel on the major roadway.
• Designers should recognize that some drivers will position themselves so that they are less than 5.4 m (17.7 ft) from the edge of the through-road traveled way. Table B lists the angular sight distance (ASD) and design speeds calculated with E = 4.4 m (14.4 ft).

Note: Based on a distance from the driver’s eye to the edge of the cross road of 5.4 m (per NCHRP 383), and a distance from the near road edge to the center of the path of the oncoming vehicle from the right (3.6 + 3.6/2) = 5.4 m.

Note: Based on a distance from the driver’s eye to the edge of the cross road of 4.4 m (per NCHRP 383), and a distance from the near road edge to the center of the path of the oncoming vehicle from the right (3.6 + 3.6/2) = 5.4 m.

• With a 13.5-degree vision angle in some restrictive vehicles, the 60-degree minimum intersection angle allowed by A Policy on Geometric Design of Highways and Streets (the "Green Book") will cause the driver’s line of sight to be obstructed by the vehicle itself and will reduce the sight distance available to the driver.
• If roadway engineers are to consider the limitations created by vehicle designs, the findings from this study suggest that a minimum intersection angle of 70 to 75 degrees will offer an improved line of sight.

None

Safety Effectiveness of Intersection Left- and Right-Turn Lanes (FHWA-RD-02-089)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Michael S. Griffith

Harwood, D.W., Bauer, K.M., Potts, I.B., Torbic, D.J., Richard,K.R., Kohlman Rabbani, E.R., Hauer, E., and Elefteriadou, L.

July 2002

254

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

All

To perform a well-designed before/after evaluation of the safety effects of providing left- and right-turn lanes for selected types of at-grade intersection design improvements.

Data were gathered for 280 improved intersections, as well as 300 similar intersections that were not improved during the study period. The types of improvement projects evaluated included installation of added left-turn lanes, installation of added right-turn lanes, and extension of the length of existing left- or right-turn lanes. Three contrasting approaches to a before/after evaluation were used: (1) yoked comparison (YC) or matched-pair approach, (2) the comparison group (CG) approach, and (3) the Empirical Bayes (EB) approach.

Independent Variables:

• Geometric design (29 variables).
• Traffic control (type of control, type of left-turn phasing, presence of pedestrian signals, presence of advanced warning signs, posted speed limit).
• Traffic volume (major-road ADT, minor-road ADT, intersection turning-movement count (morning), intersection turning-movement count (evening)).
• Traffic crashes (date, location, severity (fatal, injury, PDO), number of vehicles involved, type/manner of collision, direction of travel, actual or intended movement (through, left turn, right turn, U-turn), relationship to intersection (at intersection, not at intersection but intersection-related, not intersectionrelated), vehicle and party types (passenger car, truck, bus, pedestrian, bicycle)).

Dependent Variables:

• Intersection accident type (total crashes, fatal and injury crashes, project-related crashes, procject-related fatal and injury crashes, total crashes for individual approaches, fatal and injury crashes for individual approaches, project-related crashes for individual approaches, project-related fatal and injury crashes for individual approaches).

Intersection Safety, Left-Turn Lanes, Right-Turn Lanes, Safety Effectiveness, Before/After Evaluation, Empirical Bayes, Comparison Group

• Installation of a single left-turn lane on a major-road approach would be expected to reduce total intersection crashes at rural unsignalized intersections by 28 percent for four-leg intersections and by 44 percent for three-leg intersections.
• At urban unsignalized intersections, installation of a left-turn lane on one approach would be expected to reduce crashes by 27 percent for four-leg intersections and by 33 percent for three-leg intersections.
• At four-leg urban signalized intersections, installation of a left-turn lane on one approach would be expected to reduce crashes by 10 percent.
• Installation of a single right-turn lane on a major-road approach would be expected to reduce total intersection crashes at rural unsignalized intersections by 14 percent and crashes at urban signalized intersections by 4 percent.
• Right-turn lane installation reduced crashes on individual approaches to four-leg intersections by 27 percent at rural unsignalized intersections and by 18 percent at urban signalized intersections
• In general, turn-lane improvements at rural intersections resulted in larger percentage reductions in crash frequency than comparable improvements at urban intersections.
• The EB method provided the most accurate and reliable results for before/after evaluation of safety improvements.

Figure A. Use of regression relationship in the EB approach.

• Both added left-turn lanes and added right-turn lanes are effective in improving safety at signalized and unsignalized intersections in both rural and urban areas.
• The EB approach should be considered the most desirable approach for observational before/after evaluation of safety improvements. The CG approach should generally be considered as preferable to the YC approach, because it incorporates a comparison group consisting of multiple sites. However, both the CG and YC approaches are likely to provide overly optimistic evaluation results.
• FHWA should consider incorporating these results in the accident modification factors used for safety prediction in the Interactive Highway Safety Design Model (IHSDM) and in other ongoing initiatives, such as the Comprehensive Highway Safety Improvement Model (CHSIM).

None

Prediction of the Expected Safety Performance of Rural Two- Lane Highways (FHWA-RD-99-207)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Michael S. Griffith

Harwood, D.W., Council, F.M., Hauer, E., Hughes, W.E., and Vogt, A.

December 2000

197

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

All

This report presents an algorithm for predicting the safety performance of a rural two-lane highway.

This report presents a new approach to crash prediction that combines the use of historical crash data, regression analysis, before/after studies, and expert judgment to make safety predictions that are better than those that could be made by any of these three approaches alone.

• The recommended approach to crash prediction has its basis in published safety literature, including both before/after evaluations and regression models; is sensitive to the geometric features that are of greatest interest to highway designers; and incorporates judgments made by a broadly based group of safety experts.
• Separate crash prediction algorithms were developed for roadway segments and for three types of at-grade intersections. The total predicted crash frequency for any highway project is the sum of the predicted frequency of nonintersection-related crashes for each of the roadway segments and the predicted frequency of intersection-related crashes for each of the at-grade intersections that make up the project.
• The crash prediction algorithms for roadway segments and at-grade intersections are each composed of two components: Base models and crash modification factors. The base models were developed in separate studies by Vogt (1999) and Vogt and Bared (1998a, 1998b).

Safety, Accident Modeling, Two-Lane Highways, Roadway Segments, Accident Prediction, Geometric Design, Empirical Bayes Estimation, At-Grade Intersections

• The structure of the crash prediction algorithm, including base models, crash modification factors, calibration factors, and the EB procedure, is illustrated in the figure below. The flow diagram shown in the figure addresses the application of the crash prediction algorithm to a single roadway segment or at-grade intersection.

Figure A. Flow diagram of the crash prediction algorithm for a single roadway segment or intersection.

• The primary conclusion of this report is that a crash prediction algorithm has been developed and that this algorithm appears to be a useful tool for predicting the safety performance of rural two-lane highways.
• FHWA plans to incorporate the crash prediction algorithm for rural two-lane highways presented in this report in software for implementation as part of the IHSDM. A stand-alone version of the software may also be available for use independent of a computer-aided design (CAD) system.
• It is recommended that future enhancements be made to the crash prediction algorithm as further research is completed and that forthcoming research on rural two-lane highways be structured so that the results are obtained in a form that can be directly implemented in the crash prediction algorithm. It is also recommended that a program of additional research be undertaken with the specific goal of filling gaps in the crash prediction algorithm and expanding its scope.

None

Intersection Safety Briefing Sheets: An Introduction

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Hasson, P., and Stollof, E.

July 2002

35

http://www.tfhrc.gov/safety/intersect.htm

Literature Review

Normal

Not Specified

To provide a toolkit that contains a series of briefing sheets on various intersection safety-related topics.

The purpose of this toolkit is to enhance communications with the media, decisionmakers, the general public, and others about intersection safety.

The topical areas that are included within this intersection safety communications toolkit include:

• The National Intersection Safety Problem.
• Basic Countermeasures to Make Intersections Safer.
• Pedestrian Safety at Intersections.
• Human Factors Issues in Intersection Safety.
• Intersection Safety Enforcement.
• Traffic Control Devices: Uses and Misuses.
• Red-Light Running Issues.
• Red-Light Cameras.
• Work Zone Intersection Safety.
• Intersection Safety: Myths vs. Reality.
• Intersection Safety Resources.

Countermeasures, Intersection Safety, Pedestrian Safety, Human Factors, Red-Light Running, Work Zone Safety

The National Intersection Safety Problem:

• The following actions address ways to achieve substantial reductions in annual crash figures: (1) alter key features of the physical design of a highway or street; (2) analyze reasons for traffic conflicts at intersections; (3) engage in innovative and strategic thinking; (4) provide sustained and consistent law enforcement efforts; and (5) all levels of government must play a central role by providing both improved funding and cooperation with highway and vehicle engineers, law enforcement, and local citizen safety groups.

Basic Countermeasures to Make Intersections Safer:

• Eliminate vehicle and pedestrian conflicts when possible.
• When not possible, reduce unavoidable vehicle and pedestrian conflicts to lower the chance of a collision.
• Design intersections so that when collisions do occur, they are not as severe. (Studies have shown that providing turn lanes for left-turning vehicles can reduce crashes by 32 percent. Signalization countermeasures include using 30.5-centimeter (cm) (12-inch) signal heads; providing separate signals over each lane; installing higher intensity signals; and changing the length of signal cycles, including the yellow change interval and the red clearance interval.)
• Addition of turn lanes at intersections.
• Nontraditional intersection design.
• Pavement conditions.
• Upgrade and supplement signs.

How to Increase Pedestrian Safety at Intersections:

• Visibility: Pedestrians need to make themselves more visible during evening and nighttime hours.
• Coordination among engineers, educators, and enforcement personnel.
• Focus enforcement on motorist compliance with pedestrian safety laws, pedestrian compliance, and reducing speeding through intersections.
• Education.

Human Factors Issues in Intersection Safety:

• Driver ability to see signs, markings, and signals: Many drivers may have good vision, but are not able to see well at night because of poor sensitivity to the contrast between light and dark.
• Driver risk taking: Older drivers often take risks unknowingly because of diminished motor skills, poor vision, and reduced cognitive ability.
• Older drivers: Drivers 85 years of age and older are more than 10 times as likely as drivers in the age 40-49 group to have multiple-vehicle intersection crashes.
• Younger drivers: The youngest driver age groups have the highest traffic violation and crash involvement rates.

Intersection Safety Enforcement:

• The following are challenges to intersection enforcement: Traffic congestion, intersection signal timing, disregard for compliance with traffic control devices, and insufficient staffing for traditional enforcement.

Problems With Traffic Control Device Placement and Installation:

• Use of an improper device.
• Improper placement.
• Wrong size, color, or shape.
• Excessive installation.
• Failure to use traffic control devices at necessary locations.
• Failure to warn or notify drivers and pedestrians of unexpected, potentially hazardous conditions.

See results above.

None

Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red-Light Running

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Institute of Transportation Engineers

2003

60

http://www.tfhrc.gov/safety/intersect.htm

Literature Review (Informational Report)

Normal

Not Specified

To provide a background of the characteristics of the red-light running (RLR) problem; identify how various engineering measures can be implemented to address this problem; suggest a procedure for selecting the appropriate engineering measures and provide guidance on when enforcement, including red-light cameras (RLCs), may be appropriate.

In 2000, FHWA and the Institute of Transportation Engineers (ITE) initiated preparation of an informational report. The principal focus of this effort was to examine the engineering features of an intersection that could reduce RLR. The report is to serve as an educational tool for law enforcement agencies and others who may design RLC systems.

A panel of experts from Federal, State, and local governments, as well as academia and the private sector, was formed to share knowledge and experiences in addressing RLR using engineering countermeasures. In addition, a process was established to collect information and survey practicing engineers to collect the broadest information possible on the topic.

Red-Light Running, Intersection Design, Countermeasures

Countermeasures With Promise:

• Improve signal visibility: A total of 40 percent of red-light runners claim that they did not see the signal and another 12 percent apparently mistook the signal indication. Stricter adherence to the guidelines and standards presented in the MUTCD are needed to improve signal visibility. Countermeasures described in this report include: Placement and number of signal heads, size of the signal display, and line of sight.
• Improve signal conspicuity: The following countermeasures can be applied to capture the motorist’s attention: Redundancy by providing two red-signal displays within each signal head, LED signal lenses, backplates, and strobe lights.
• Increase likelihood of stopping: Countermeasures detailed in this report include: "Signal Ahead" signs, advanced-warning flashers, rumble strips, left-turn signal sign, and pavement surface condition.
• Address intentional violations: The following countermeasures relate to signal timing to prevent drivers from trying to "beat" the yellow signal: Signal optimization, modification to signal cycle length, yellow change interval, all-red clearance interval, and dilemma zone protection.
• Eliminate need to stop: This can be done by removing the signal or redesigning the traditional intersection. Other countermeasures in this category include: Unwarranted signals, roundabout intersection design, and flash mode for signals.

Process for Addressing Safety Problems Related to Red-Light Running:

• Confirm that there is a safety problem, conduct an engineering analysis to identify factors that might be causing the problem, identify alternative countermeasures, select the most appropriate single or combined set of countermeasures, and implement and monitor the countermeasures.

• Research cited in this report suggests that "intentional" red-light runners are most affected by enforcement countermeasures, while "unintentional" red-light runners are most affected by engineering countermeasures.
• The report also establishes the essential need for sound engineering at an intersection for the successful implementation of long-term and effective enforcement activities, particularly automated enforcement.
• The report also concludes that education initiatives can be an effective complement for any approach or as a stand-alone program.
• RLR is recognized as a complex problem requiring a reasoned and balanced application of education, enforcement, and engineering.

Future improvements in the reduction of RLR violations and crashes can be achieved through the following future activities: R&D, improved data related to RLR crashes, improved guidelines and standards, and improved procedures and programs.

Vehicle-Based Countermeasures for Signal and Stop Sign Violations, Task 1: Intersection Control Violation Crash Analyses, and Task 2: Top-Level System and Human Factors Requirements (DOT-HS-809-716)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Kerrin Bressant

Lee, S.E., Knipling, R.R., DeHart, M.A., Perez, M.A., Holbrook, G.T., Brown, S.B., Stone, S.R., and Olson, R.L.

March 2004

209

http://www-nrd.nhtsa.dot.gov/departments/nrd-12/pubs_rev.html

Crash/Demographic Statistical Analysis

Normal

Light Vehicles

Task 1: To characterize light-vehicle violation crashes so that intersection violation countermeasures could be developed in subsequent project tasks.

Task 1 of this project involved a series of database analyses to create a clear problem definition for intersection violation crashes.

• Task 1 analyses included an overall crossing-path (CP) crash problem size description by injury severity level, followed by increasingly detailed analyses of crash type, traffic control devices, violation distributions and types, causal factors, speed behavior, and infrastructure components.
• Analyses included identification of major causal factors for each subtype of intersection control violation.
• The Virginia Tech Transportation Institute (VTTI) used the NHTSA General Estimates System (GES) database to characterize the violation CP crash problem for the years 1999 and 2000.
• Task 1 analyses were performed in a top-down manner, beginning with defining the overall crash problem and then refining the analyses in later subtasks.

Intersection Crashes, Stop Sign Violations, Signal Violations, Forward Collision Warning, Traffic Control Violation Warning, Crash Countermeasures

• Left-turn crashes make up the majority of the CP crash types, at about 52 percent for the years 1998 through 2000.
• The next most prevalent type is the straight CP crash type, at about 30 to 35 percent, followed by unknown CP crashes at 7 to 11 percent.
• Right-turn crashes are the least common, at about 6 percent of all CP crashes for 1998 through 2000.
• Stop-sign CP crashes in which only one vehicle had a stop sign were four or five times more prevalent than crashes in which both vehicles had a stop sign.
• Those citation types deemed to be most amenable to the Intersection Crash Avoidance, Violation (ICAV), countermeasures were speeding, reckless driving, failure to yield right of way, and running a stop sign or traffic signal; thus, these were the violation types explored for this subtask.
• In terms of the overall analysis, for the left- and right-turn crash types, more drivers were cited who made turning precrash maneuvers than straight precrash maneuvers.
• Among all crash types and injury levels, driver distraction and inattention was the largest primary contributing factor, at 37 percent. This finding validates some of the assumptions made in the early stages of the ICAV project, in that one of the primary purposes of the ICAV system is to capture the attention of the inattentive or distracted driver.

Figure A. Percentage of violation types across all CP crash types, 2000 GES (bars represent 95 percent confidence interval).

• Although an ICAV-target crash population could not be defined and determined with specificity in task 1 based on GES variables, populations likely to be addressable by the countermeasure concept were identified as part of subtask 1.4.
• An estimated 261,000 light-vehicle crashes in 1999 and 162,000 in 2000 occurred at intersections where one of the two vehicles had a stop sign and was charged with a violation. There were an estimated 133,000 crashes in 1999 and 99,000 crashes in 2000 involving traffic signal violations. These crash populations could be target crashes for ICAV.

• This review is part 1 of a two-part review and covers task 1 of the report.
• This report summarized tasks 1 and 2 of the larger Vehicle-Based Countermeasures for Signal and Stop Sign Violations project

Vehicle-Based Countermeasures for Signal and Stop Sign Violations, Task 1: Intersection Control Violation Crash Analyses, and Task 2: Top-Level System and Human Factors Requirements (DOT-HS-809-716)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Kerrin Bressant

Lee, S.E., Knipling, R.R., DeHart, M.A., Perez, M.A., Holbrook, G.T., Brown, S.B., Stone, S.R., and Olson, R.L.

March 2004

209

http://www-nrd.nhtsa.dot.gov/departments/nrd-12/pubs_rev.html

Literature Review

Normal

Light Vehicles

Task 2: To determine the high-level requirements for a countermeasure system to address the intersection control violation problem.

Task 2 of this project comprises a literature review based on a review of more than 60 reports and other publications related to intersection crashes and countermeasures.

This task 2 literature review outlines the problem-size description for intersection crashes, the general causal factors for the intersection crashes of interest, the approaches taken for this problem, and the components required to make such a system work. Major topics addressed include:

• Intersection crash problem description:
  • Previous analytical studies of crash data.
  • Studies of RLR and camera enforcement.
• Computation algorithm parameters (e.g., brake reaction time, models of braking performance).
• Driver-vehicle interface (DVI) considerations (also see appendix A).
• Behavioral adaptation to countermeasures.
• Previously tested vehicle-based countermeasures for intersection crashes/violations (with emphasis on the NHTSA-sponsored Veridian Intersection Collision Avoidance program).

Intersection Crashes, Stop Sign Violations, Signal Violations, Forward Collision Warning, Traffic Control Violation Warning, Crash Countermeasures

• Preliminary requirements and specifications for Intersection Crash Avoidance, Violation (ICAV) deployment, Field Operational Test (FOT), and test-bed systems were developed.
• Based on the requirements and specifications developed in task 2, a set of specifications requiring further testing and not definitively scheduled to be performed by any other group (such as the Crash Avoidance Metrics Partnership (CAMP) or the Infrastructure Consortium) is presented.
• The figure below depicts the three-phase ICAV development process and feedback loop.

Figure A. Three-phase ICAV development process and feedback loop.

Preliminary requirements and specifications for ICAV deployment, FOT, and test-bed systems were developed as follows: Stop Sign Deployment System:

• Position system: Lateral vehicle position accuracy, longitudinal vehicle position accuracy, stopping location accuracy relative to stop bar, vehicle offset, update rate, data latency.
• In-vehicle sensors: Speed (four specifications), acceleration (four specifications), braking status (four specifications), heading angle (four specifications).
• Computations: Computational speed (latency), false alarm rate, miss rate, driver acceptance.
• Driver-vehicle interface: Levels of alert, recommended modality, visual display (seven specifications), auditory display (five specifications), haptic display (four specifications).

Stop Sign FOT System:

• Positioning: Maximum time loss for positioning data, lateral vehicle position accuracy, longitudinal vehicle position accuracy, update rate, vehicle offset, stopping location accuracy, data latency.
• In-vehicle sensors: Speed (four specifications), acceleration (four specifications), braking status (four specifications), heading angle (four specifications).
• Computations: Computational speed (latency), false alarm rate, miss rate, driver acceptance.
• Driver-vehicle interface: Levels of alert, recommended modality, visual display (seven specifications), auditory display (five specifications), haptic display (four specifications).

Signalized Intersection Deployment System (communications only; others are the same as for stop sign case):

• Communications link with infrastructure: Communication path, data latency, update rate, range, content of data stream (packet content), packet size.

Signalized Intersection FOT System (communications only; others are the same as for stop sign case):

• Communications link with infrastructure: Communication path, data latency, update rate, range, content of data stream (packet content), packet size.

• This review is part 2 of a two-part review and covers task 2 of the report.
• This report summarized tasks 1 and 2 of the larger Vehicle-Based Countermeasures for Signal and Stop Sign Violations project.

Older Driver Perception-Reaction Time for Intersection Sight Distance and Object Detection, Volume I: Final Report (FHWA-RD-93-168)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Elizabeth Alicandri

Lerner, N.D., Huey, R.W., McGee, H.W., and Sullivan, A.

January 1995

116

None

On-Road Study

Normal

Not Specified

To determine the appropriate perception-reaction time (PRT) values for use in design equations for stopping sight distance (SSD), intersection sight distance (ISD), and decision sight distance (DSD).

Four on-road experiments investigated whether the assumed values for driver PRT used in AASHTO design equations adequately represent the range of actual PRT for older drivers.

Case III (Stop-Controlled) Intersection Sight Distance:

• A total of 102 subjects (thirty-three 20 to 40 year olds, thirty-five 65 to 69 year olds, and thirty-four age 70 plus) drove their vehicles over an extended route, including a number of stop-controlled intersections.
• The experiment included a variety of intersection characteristics and left-turn, right-turn, and crossing vehicle maneuvers.

Stopping Sight Distance:

• Data were obtained from 116 subjects (thirty 20 to 40 year olds, forty-three 65 to 69 year olds, and forty-three age 70 plus).
• Subjects were driving their cars along a route and did not know that an event requiring rapid braking would occur.
• At one point along the route, protected from other traffic, a crash barrel rolled from behind brush on a berm and onto the edge of the roadway.
• The driver’s PRT was measured from the moment the barrel came into the driver’s view until the driver stepped on the brake.

Decision Sight Distance:

• Subjects drove their vehicles along an extended route that included both freeway and arterial sections.
• At various sites, lane-change maneuvers were required by roadway features that were appropriate to the decision sight distance model.
• Drivers verbalized when they first noted the necessity of changing lanes; they also verbally indicated the cue that informed them of the need to make the maneuver.
• PRT was measured from the point where the cue first became visible to the moment the driver verbalized the need to change lanes.

Gap/Lag Acceptance:

• A total of 138 subjects (fifty-two 20 to 40 year olds, thirty-nine 65 to 69 year olds, and forty-seven age 70 plus) participated.
• Subjects were not actually driving. They viewed traffic from a vehicle on the roadside and made decisions about when it would be safe to make various maneuvers.

Older Drivers, Aging, Perception-Reaction Time, Sight Distance

Case III (Stop-Controlled) Intersection Sight Distance:

• The results indicated that older drivers did not have longer PRT than younger drivers.
• The 85^th percentile PRT closely matched the AASHTO design equation value of 2.0 s.
• Although older drivers did not appear to require more time at intersections, there was an age-by-gender interaction. Women in the oldest group were slower than men for both PRT and maneuver times.

Stopping Sight Distance:

• Driver reactions: Of the 116 valid subjects, 101 (87 percent) made some overt vehicle maneuver in reaction to the emergence of the crash barrel (36.2 percent swerved only, 7.8 percent braked only, and 43.1 percent both braked and swerved).
• Brake PRT: The mean brake reaction time, overall and for various subgroups, was about 1.5 s, with a standard deviation of about 0.4 s (see table A). The 85^th percentile brake reaction time is approximately 1.9 s.
• There were apparent differences in the distribution of PRT among age groups.
• Younger drivers accounted for most of the fastest PRT, but there were no age differences in the 50^th or 85^th percentiles.
• All observed PRT were encompassed by the current AASHTO design value of 2.5 s.

Decision Sight Distance:

• Although observed DSD values were generally longer with increasing driver age, the 85^th percentile PRT for all age groups were well below AASHTO design assumptions (see table B).

Gap/Lag Acceptance:

• Younger subjects accepted shorter gaps and rejected lags later than older subjects.
• Averaged over all conditions, the point at which 50 percent of the subjects would accept a gap was just over 1 s longer for the oldest group than it was for the youngest group.
• The oldest group had a mean lag rejection point that was about 0.5 s longer than the younger subjects.

• Based on these findings and consideration of the implications of changes in PRT for sight distance requirements, no changes to the design PRT values, based on older driver performance, were recommended for ISD, SSD, or DSD.
• Overall, it would appear that to the extent current models are reasonable and are appropriate analogs of actual driver behavior, the PRT design parameters of those models are generally adequate to accommodate most older drivers.

None

Association of Selected Intersection Factors With Red-Light Running Crashes (FHWA-RD-00-112)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Mohamedshah, Y.M., Chen, L.W., and Council, F.M.

May 2000

6

http://www.tfhrc.gov/library/library.htm

Crash/Demographic Statistical Analysis

Normal

All

To examine selected geometric characteristics of intersections and their impact on red-light running (RLR) crash rates and to establish a relationship between them.

• The major questions addressed in this report concerning RLR crashes are:
  • Does the width of the cross street have any effect on RLR crash risk?
  • What is the relationship of other select intersection characteristics?
  • Using this information, how can one better target urban intersections for traffic law enforcement techniques such as RLR cameras or heightened intersection enforcement coupled with publicity?

State Databases Used:

• Data from the Highway Safety Information System (HSIS) database for California was reviewed.
• Crash files for a 4-year period (from 1993 through 1996) and the intersection data for 1996 were used to develop a model that shows the relationship of geometric variables to RLR crashes.

Analysis Methods and Model Development:

• Limited contingency table analysis was done to examine the similarities and the differences between RLR crashes and all crashes at urban signalized intersections (USI).
• Regression-type models were developed to examine the effects of intersection characteristics on RLR crash frequencies.
• Separate models were developed to predict RLR crashes for streets defined in the raw intersection file as "mainline" (i.e., primarily higher volume streets) and for streets defined as "cross streets" (i.e., primarilylower volume streets).

Red–Light Running, Intersections, Urban Signalized Intersections

Effect of Cross-Street Lanes:

• The negative-binomial model for the cross street shows that there is a 7-percent increase in cross-street RLR crashes for each one-lane increase when one controls for signal operation type, opposite street ADT, and left-turn channelization (see figure A).
• However, the number of cross-street lanes did not have a significant effect on mainline RLR crashes.

Effect of ADT:

• RLR crashes on the mainline seemed to increase with higher entering street ADT, as well as with the increase in cross-street ADT per lane.
• Similar to the mainline, RLR crashes involving vehicles entering from the cross street tended to increase with higher entering street ADT. However, in contrast to the mainline finding, RLR crashes for vehicles entering from the cross street did not increase with the opposite-street ADT per lane.

Effect of Traffic Control:

• Fully actuated signals tend to have more crashes per approaching street than approaches with semi–actuated and pretimed signals (35 to 39 percent higher than pretimed) when other factors are held constant (see figure B).

• The results obtained from the model show that the traffic volume on both the entering and crossing streets, the type of signal in operation at the intersection, and the width of the cross street (as measured by the number of cross-street lanes) are the major variables affecting RLR crashes.
• The intersections with higher entering volumes on the mainline and cross streets, especially intersections with high volumes on cross streets; intersections where the volume on a minor road is relatively high, coupled with a wide mainline street; and locations with fully actuated signals would be considered as highpriority intersections for such treatments as installing cameras that detect RLR or heightened spot enforcement coupled with publicity.

None

Analysis of Crossing-Path Crashes (DOT-HS-809-423)

National Highway Traffic Safety Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Not Specified

Najm, W.G., Smith, J.D., and Smith, D.L.

July 2001

76

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

All Vehicles

To define the problem of crossing-path (CP) crashes in the United States. This analysis of CP crashes is concerned with understanding the precrash scenarios in order to evaluate proposed countermeasure designs.

This report separates CP crashes into five common scenarios that represent vehicle movements immediately prior to the crash. This report also describes the locations where CP crashes occurred in terms of their relationship to a roadway junction and the type of traffic control device at these locations.

• The NHTSA National Automotive Sampling System (NASS) was principally used in this analysis.
• This study also queried the 1998 General Estimates System (GES) for fatal crashes to see if the fatality demographics followed the crash demographics, or if some types of CP crash scenarios had more fatalities than others.
• These GES fatal crash counts were also compared to statistics from the 1998 Fatality Analysis ReportingSystem (FARS).

Crossing-Path Crash, Traffic Conflict, Crash Scenario, Crash Frequency, Opposite Direction Conflict, Lateral Direction Conflict, Merge Conflict, Straight Crossing Paths, Relationship to Junction, Traffic Control Device, Violation Charged, Vision Obstruction, Driver Distraction, Pedestrian, Pedalcyclist.

• Five common CP crash scenarios: (1) left turn across path–opposite direction conflict (LTAP/OD); (2) left turn across path–lateral direction conflict (LTAP/LD); (3) left turn into path–merge conflict (LTIP); (4) right turn into path–merge conflict (RTIP); and (5) straight crossing paths (SCP).
• CP crashes accounted for about 1.72 million police-reported collisions in 1998 based on the GES statistics.
• GES estimated that more CP crashes occurred at unsignalized intersections and driveways than at signalized intersections (about 42 percent of CP crashes occurred in the presence of signals, while the remaining 58 percent occurred at unsignalized intersections).
• The analysis of the 1998 GES revealed that CP crashes at intersections with no controls had the highest fatality rates
• "Failure to Yield Right of Way" was the most dominant violation in all CP crash scenarios at intersections and driveways controlled by stop signs or with no controls (see table below).
• Alcohol and drug violations were charged to fewer than 2 percent of the vehicles involved in CP crashes at intersections and driveways.
• About 9 percent of drivers attributed vision obstruction as a contributing factor in LTAP crashes at intersections with either no controls or stop signs. Vision obstruction was also reported by about 16 percent and 10 percent of drivers involved in LTAP crashes at driveways with stop signs and no controls, respectively.
• Pedestrian crashes are typically severe and account for about 15 percent of the total collision fatality population each year.
• Pedestrian and pedalcyclist collisions are more likely to be fatal at nonjunction locations than at intersections, and are more likely to be fatal at intersections than at driveways.
• The most dominant precrash event of pedestrian and pedalcyclist collisions involved a vehicle that was in the process of turning/merging, was preparing to turn/merge, or had just completed a turning/merging maneuver.

Note: Empty cells refer to scenarios that had no crashes in the 1998 GES sample.

See Key Results above.

None

Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, NCHRP Report 500

National Cooperative Highway
Research Program Transportation Research Board
500 Fifth Street, N.W.
Washington, DC 20001

COTR:

Not Specified

Neuman, T.R., Pfefer, R., Slack, K.L., Hardy, K.K., Harwood, D.W., Potts, I.B., Torbic, D.J., and Kohlman Rabbani, E.R.

2003

71

http://trb.org/news/blurb_browse.asp?id=2

Guidelines and Recommendations

Normal

All

To provide guidance to highway agencies that want to implement safety improvements at unsignalized intersections. Includes a variety of strategies that may be applicable to particular locations.

NCHRP Project 17-18(3) is a series of guides to assist State and local agencies in reducing injuries and fatalities in targeted areas. Each guide includes a brief introduction, a general description of the problem, the strategies/countermeasures to address the problem, and a model implementation process.

The strategies in this guide were identified from a number of sources, including the literature, contact with State and local agencies throughout the United States, and Federal programs. Some of the strategies are widely used, while others are used at a State or even local level of the safety system.

Unsignalized Intersections, Traffic Control Devices, Geometric Design Improvements, Traffic Calming

The objectives for improving safety at unsignalized intersections and the strategies to achieve them are listed below.

• Improve management of access near unsignalized intersections: Implement driveway closures/relocations and implement driveway turn restrictions.
• Reduce the frequency and severity of intersection conflicts through geometric design improvements: Provide the following at intersections: Left-turn lanes, offset left-turn lanes, bypass lanes on shoulders at T-intersections, left-turn acceleration lanes at divided-highway intersections, right-turn lanes, offset right-turn lanes, right-turn acceleration lanes, full-width paved shoulders, signage to restrict or eliminate turning maneuvers. Close or relocate high-risk intersections. Convert four-leg intersections to two T-intersections. Convert offset Tintersections to four-leg intersections. Realign intersection approaches to reduce or eliminate intersection skew. Use indirect left-turn treatments to minimize conflicts at divided-highway intersections. Improve pedestrian and bicycle facilities to reduce conflicts between motorists and nonmotorists.
• Improve sight distance at unsignalized intersections: Provide clear sight triangles on stop- or yield-controlled approaches to intersections. Provide clear sight triangles in the medians of divided highways near intersections. Change horizontal and/or vertical alignment of approaches to provide more sight distance. Eliminate parking that restricts sight distance.
• Improve availability of gaps in traffic and assist drivers in judging gap sizes at unsignalized intersections: Provide an automated real-time system to inform drivers of the suitability of available gaps for making turning and crossing maneuvers. Provide roadside markers or pavement markings to assist drivers in judging the suitability of available gaps for making turning and crossing maneuvers. Re-time adjacent signals to create gaps at stop-controlled intersections.
• Improve driver awareness of intersections as viewed from the intersection approach: Improve visibility of intersections by providing enhanced signage and delineation. Improve visibility of the intersection by providing lighting. Install splitter islands on the minor-road approach to an intersection. Provide a stop bar on minor-road approaches. Install larger regulatory and warning signs at intersections. Call attention to the intersection by installing rumble strips on approaches. Provide dashed markings for major-road continuity across the median opening at divided-highway intersections. Provide supplementary stop signs mounted over the roadway. Provide pavement markings with supplementary messages. Provide improved maintenance of stop signs. Install flashing beacons at stop-controlled intersections.
• Choose appropriate intersection traffic control to minimize crash frequency and severity: Avoid signalized through roads. Provide all-way stop control at appropriate intersections. Provide roundabouts at appropriate locations.
• Improve driver compliance with traffic control devices and traffic laws at intersections: Provide targeted enforcement to reduce stop sign violations. Provide targeted public information and education on safety problems at specific intersections.
• Reduce operating speeds on specific intersection approaches: Provide targeted speed enforcement. Provide traffic calming on intersection approaches through a combination of geometrics and traffic control devices. Post appropriate speed limit on intersection approaches.
• Guide motorists more effectively through complex intersections: rovide turn-path markings. Provide a double yellow centerline on the median opening of a divided highway at intersections. Provide lane assignment signage or marking at complex intersections.

The model process for implementing a program of strategies for any given emphasis area of the AASHTO Strategic Highway Safety Plan is listed below:

• Model Process: Identify and define the problem; recruit appropriate participants for the program; establish crashreduction goals; develop program policies, guidelines, and specifications; develop alternative approaches to addressing the problem; evaluate alternatives and select a plan; submit recommendations for action by top management; develop a plan of action; establish foundations for implementing the program; carry out the action plan; and assess and transition the program.

See Key Results above.

This is the fifth volume of Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, NCHRP Report 500 (a series in which relevant information is assembled into single, concise volumes, each pertaining to specific types of highway crashes or contributing factors).

Intersection Collision Avoidance Using ITS Countermeasures, Performance Guidelines, Final Report (DOT-HS-809-171)

U.S. Department of Transportation
National Highway Traffic
Safety Administration
Office of Advanced Safety Research
Washington, DC 20590

COTR:

Not Specified

Pierowicz, J., Jocoy, E., Lloyd, M., Bittner, A., and Pirson, B.

September 2000

172

http://www.its.dot.gov/itsweb/EDL_webpages/webpages/SearchPages/Alpha_Search.cfm

Closed-Track Study

Imminent Crash (ICA)

Light Vehicles

To develop an Intersection Collision Avoidance System (ICAS) test bed, implement the systems on a vehicle, and perform testing to determine the potential effectiveness of the system in preventing intersection crashes.

• This report documents the analyses performed in support of the Intersection Collision Avoidance Using ITS Countermeasures program.
• The overall effort consisted of three phases: Analytical, design, and implementation. This report is the final product of the implementation phase.

There were three technical phases associated with this project: (1) analytical, (2) design, and (3) implementation.

The analytical tasks performed in phase I indicated that while crashes occurred at intersections with varying configurations, the causes and major characteristics of these crashes demonstrated similar features. Three countermeasure concepts were developed from the analyses of these crashes.

In phase II, an Intersection Collision Avoidance (ICA) test-bed vehicle was designed based on the functional descriptions of the countermeasure concepts developed in phase I.

The test-bed vehicle was constructed and tested in phase III.

Intersection Collision Avoidance System (ICAS), Performance Guidelines, Driver-Vehicle Interface (DVI), ICAS Test Bed, Threat Detection System

• The ICAS test-bed vehicle was a Ford Crown Victoria that supported the following features:
  • Threat detection system.
  • Geographical Information System/Global Positioning System (GIS/GPS).
  • Driver-Vehicle Interface, including Head-Up Display (HUD), auditory system, and haptic warning system.
  • Vehicle systems that integrate the ICAS equipment into the test-bed vehicle.
• The two primary defensive collision scenarios, left turn across path (LTAP) and violation of traffic control, were encountered during testing of the countermeasures; the countermeasure was found to be able to detect and warn the driver about an impending collision.
• The Differential GPS/GIS system software was able to access the map database in real time to support transfer of intersection information to the threat detection system and unsignalized intersection warning system in a timely manner.
• The physical size limitations of the antennas for the limited coverage system and the full coverage system may make lane discrimination difficult because the beam width is too large.

Design Guidelines:
The following guidelines were used in designing the on-vehicle ICAS:

• System should not rely on systems on other vehicles.
• There should be minimum reliance on infrastructure.
• Minimum crash severity should occur if crash cannot be completely avoided.
• System should operate in all weather.
• Maximum use of intersection parameters derived from on-board GIS map and GPS.

Recommendations:

• Integrate LTAP sensor algorithms developed on the ICAS into the NHTSA IVI program.
• Continue development of map-based unsignalized intersection system.
• Fund development of forward-viewing, wide-field sensor.
• Investigate use of signal-to-vehicle communications to improve ICAS effectiveness.
• Continue investigation of DVI effectiveness and driver acceptance.

None

Influence of Traffic Signal Timing on Red-Light Running and Potential Vehicle Conflicts at Urban Intersections

(Transportation Research Record 1595, pp. 1-7)

Insurance Institute for Highway Safety
1005 North Glebe Road
Arlington, VA 22201

COTR:

Not Specified

Retting, R.A., and Greene, M.A.

1997

7

None

Field Test

Normal

Not Specified

To examine vehicle actions in relation to change-interval timing at intersections where the all-red interval or the yellow interval, or both, was lengthened.

Data were collected during an experiment in an urban location involving changes in signal timing at some 10 intersections. Observations included the proportion of signal cycles with vehicles entering on a red light and the proportion of vehicles exiting the intersection after the onset of a conflicting green signal.

Study Site:

• Research was conducted in a medium-sized city in New York State.

Intersection Selection:

• To be eligible for selection, an intersection required a yellow or an all-red phase, or both, that was shorter than the value computed using the Institute of Transportation Engineers (ITE)-proposed recommended practice for determining vehicle change intervals.
  • This procedure computes yellow interval timing as a function of approach speed and grade, along with assumed values for perception-reaction time, deceleration rate, and acceleration caused by gravity.
• From these intersections, 10 were chosen at random for the study. Each intersection contributed 2 sites, for a total of 20 sites.

Data Collection:

• Fifty-six measurement sessions were conducted.
• Observers used portable laptop computers to record information about each vehicle that approached the site and entered after the onset of the yellow signal.
• There were three categories of cycles: (1) violation cycles (those with at least one red-light run or one late exit by a through vehicle), (2) nonviolation cycles (those in which at least one vehicle approached the site during the yellow or red signal and then stopped or turned), and (3) inactive cycles (those in which no vehicles approached or entered the site).

Red-Light Violations, Intersection Safety, All-Red Interval, Yellow Interval

Red-Light Running Study:

• The results indicated that red-light running (RLR) is low for sites where the all-red signal length is below about 55 percent of the ITE value, and there is a positive slope up to about 80 percent of the ITE value, followed by a negative slope.
• The results showed that RLR decreases when yellow intervals are increased.

Late-Exit Study:

• The results show a downward trend from about 70 percent of the ITE-proposed recommended timing (i.e., as the length of the all-red period increases, the percentage of cycles with late exits decreases).
• The results show a trend to support the finding that with the exception of a few sites with long yellow signals, sites with shorter yellow signals tend to have more late exits.
• Yellow timing was lengthened at some sites. Four sites (A, F, P, and Q) had both intervals changed, and showed substantial decreases in the proportion of late exits.
• Four other sites (B, I, M, and N) had the yellow timing lengthened. All sites, except N, showed substantial decreases in the proportion of late exits.
• In wave 3, sites Q, R, and O had about the same all-red signal timing with about the same percentage of late exits. Site P strongly contrasted with this pattern; the all-red timing was increased in wave 3 from 105 to 112 percent of the ITE value; however, late exits increased from 3 to 11 percent.

• The RLR study shows that increasing the length of the yellow signal toward the ITE recommendations significantly decreased the chance of RLR. The length of the all-red interval did not seem to affect RLR. Finally, habituation to the longer yellow appeared to be confined to a single site.
• The results indicate that change intervals set closer to ITE’s proposed recommended practice can reducered-light violations and potential right –angle vehicle conflicts and that such safety benefits can be sustained.

None

Roundabouts: An Informational Guide (FHWA-PL-00-067)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Joe Bared

Robinson, B.W., Rodegerdts, L., Scarborough, W.,
Kittelson, W., Troutbeck, R., Brion, W., Bondzio, L.,
Courage, K., Kyte, M., Mason, J., Flannery, A., Myers, E., Bunker, J., and Jacquemart, G.

June 2000

284

None

Informational Guide

Normal

Not Specified

To provide an informational guide on the use of roundabouts.

The guidance supplied in this document is based on established international and U.S. practices and is supplemented by recent research. The guide is comprehensive in recognition of the diverse needs of transportation professionals and the public for introductory material through design detail, as well as the wide range of potential applications of roundabout intersections.

This guide has been developed with the input from transportation practitioners and researchers around the world.

Roundabouts, Traffic Circles, Intersections, Traffic Control, Intersection Design, Intersection Performance, Intersection Safety, Highway Capacity

Policy Considerations:

• Safety: Roundabouts have been demonstrated to be generally safer for motor vehicles and pedestrians than other forms of at-grade intersections.
• Vehicle delay and queue storage: When operating within their capacity, roundabout intersections typically operate with lowervehicle delays than other intersection forms and control types.
• Delay of major movements: Since all intersection movements have equal priority at a roundabout, major-street movements may be delayed more than desired.
• Spatial requirements: Roundabouts usually require more space for the circular roadway and central island than the traditional.
• Traffic calming: By reducing speeds, roundabouts complement other traffic-calming measures.
• Pedestrians: Pedestrian crossings should be set back from the yield line by one or more vehicle lengths.
• Bicycles: Bicycle lanes through roundabouts should never be used.
• Large Vehicles: Design roundabouts to accommodate the largest vehicle that can reasonably be expected.
• Transit: Public transit buses should not be forced to use a truck apron to negotiate a roundabout.

Planning:

• Planning steps: Consider the context; etermine a preliminary lane configuration and roundabout category based on capacity requirements; identify the selection category; perform the analysis appropriate to the selection category; determine the space requirements; and, if additional space must be acquired, an economic evaluation may be useful.
• Considerations of context: Consider whether the roundabout will be part of a new roadway, the first in the area, or a retrofit of an existing intersection.
• Number of entry lanes: The volume-to-capacity ratio of any roundabout leg is recommended to not exceed 0.85.
• Comparing operational performance of alternative intersection types: Roundabouts may offer an effective solution at twoway, stop-controlled intersections with heavy left turns from the major street. Roundabouts work better when the proportion of minor-street traffic is higher. A substantial part of the delay-reduction benefit of roundabouts, compared to all-way stopcontrolled intersections, comes during off-peak periods.
• Space requirements: There are design templates in appendix B that may be used to determine initial space requirements.

Operation:

• Traffic operation at roundabouts: Approach speed is governed by the approach roadway width, roadway curvature, and approach volume. The following geometric elements affect entry capacity: Approach half width, entry width, entry angle, and average effective flare length.
• Data requirements: Different sizes of vehicles have different capacity impacts; passenger cars are used as the basis for comparison. Entry flow and circulating flow for each approach are the volumes of interest for roundabout capacity analysis, rather than turning-movement volumes.
• Capacity: Roundabouts should be designed to operate at no more than 85 percent of their estimated capacity. Circulating flow should not exceed 1,800 vehicles per hour (veh/h) at any point in a single-lane roundabout. Exit flows exceeding 1,200 veh/h may indicate the need for a double-lane exit.
• Performance analysis: Key performance measures for roundabouts are degree of saturation, delay, and queue length.

Geometric Design:

• General design principles: Increasing vehicle-path curvature decreases relative speeds between entering and circulating vehicles, but also increases side friction between adjacent traffic streams in multilane roundabouts. The entry-path radius should not be significantly larger than the circulatory radius.
• Geometric elements: The following geometric elements are discussed in detail: Inscribed-circle diameter, entry width, circulatory roadway width, central island, entry curves, exit curves, pedestrian crossing location and treatments, splitter islands, stopping sight distance, intersection sight distance, vertical considerations, bicycle provisions, sidewalk treatments, parking considerations and bus stop locations, and right-turn bypass lanes.
• Rural roundabouts: Roundabout visibility is a key design element at rural locations. Curbs should be provided at all rural roundabouts. Extended splitter islands are recommended.

Traffic Design and Landscaping:

• Signing: Yield signs are required on all approaches. One-way signs establish the direction of traffic flow. Lane-use control signs are generally not recommended. Exit guide signs reduce the potential for disorientation.
• Pavement markings: Yield lines provide a visual separation between the approach and the circulatory roadway. Raised pavement markers are useful supplements to pavement markings. Zebra crosswalks provide an important visual cue for drivers and pedestrians.
• Illumination: Lighting from the central island causes vehicles to be backlit and less visible. Special consideration should be given to lighting pedestrian crossing and bicycle merging areas.

See Key Results above.

None

Signalized Intersections: Informational Guide (FHWA-HRT-04-091)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Joe Bared

Rodegerdts, L.A., Nevers, B., Robinson, B., Ringert, J., Koonce, P., Bansen, J., Nguyen, T., McGill, J., Stewart, D., Suggett, J., Neuman, T., Antonucci, N., Hardy, K., and Courage, K.

August 2004

369

None

Informational Guide

Normal

Not Specified

To provide a single, comprehensive document with methods for evaluating the safety and operations of signalized intersections and tools to remedy deficiencies.

The treatments in this guide range from low-cost measures such as improvements to signal timing and signage, to high-cost measures such as intersection reconstruction or grade separation. Topics covered include: Fundamental principles of user needs, geometric design, and traffic design and operation; safety and operational analysis techniques; and a wide variety of treatments to address existing or projected problems, including individual movements and approaches, pedestrian and bicycle treatments, and corridor techniques.

This guide takes a holistic approach to address signalized intersections and considers the safety and operational implications of a particular treatment on all system users. It is organized into the following parts:

• Fundamentals.
• Project Process and Analysis Methods.
• Treatments.

Signalized Intersections, Intersection Safety, Intersection Design, Intersection Performance, Intersection Treatments

Part I: Fundamentals

User Needs:

• The following items offer key information regarding the application of human factors principles in the analysis and design of a signalized intersection:
  • All road users must first recognize signalized intersections before they can respond.
  • Adequate illumination for nighttime operations is required.
  • Navigational information must be available sufficiently in advance.
  • Signal indications must be visible from a sufficient approach distance.
  • Phasing and clearance intervals for both vehicles and pedestrians must be suited for a mix of road users.
  • Geometric aspects of the intersection must be clear.
  • Route through the intersection itself must be explicit in order to avoid vehicles encroaching on each other.

Geometric Design:

• This chapter addresses the principles of channelization, number of intersection approaches, intersection angle, horizontal and vertical alignment, corner radius and curb ramp design, detectable warnings, access control, sight distance, and pedestrian and bicycle facilities.

Traffic Design and Illumination:

• This chapter deals with the traffic signal hardware and software. The proper application and design of the traffic signal is a key component in improving the safety and efficiency of the intersection. Topics discussed include: Traffic signal control types, traffic signal phasing, vehicle and pedestrian detection, traffic signal pole layout, traffic signal controllers, basic signal timing parameters, signage and pavement markings, and illumination.

Part II: Project Process and Analysis Methods

• The following are the steps discussed in the project process: Project initiation, identify stakeholder interests and objectives, collect data, identify the problem, identify the cause of the problem, and select a treatment.
• The following steps are described in the safety analysis method: Selection of an intersection, identification of potential problems, identification of possible treatments, and improvement plan development.

Part III: Treatments

Systemwide Treatments:

• Treatments in this chapter apply to roadway segments located within the influence of signalized intersections and to intersections affected by traffic flow along a corridor. These treatments primarily address safety concerns associated with rearend collisions, turbulence related to vehicles turning midblock from driveways or nonsignalized intersections, and coordination deficiencies associated with how traffic progresses from one location to another. The following four specific treatments are examined: Median treatments, access management, signal coordination, and signal preemption and/or priority.

Intersectionwide Treatments:

• Pedestrian treatments: Reduce curb radius, provide curb extensions, modify stop bar location, improve pedestrian signal displays, and modify pedestrian signal phasing and grade-separate pedestrian movements.
• Bicycle treatments:Provide bicycle box and bicycle lanes.
• Transit treatments:Relocate transit stop.
• Traffic control treatments:Change signal control from pretimed to actuated, modify yellow change interval and/or red clearance interval, modify cycle length, and late night/early morning flash removal.
• Street lighting and illumination:Provide or upgrade illumination.

Alternative Intersection Treatments:

• Intersection reconfiguration and realignment treatments:Remove intersection skew angle, remove deflection in travel path for through vehicles, convert four-leg intersection to two T-intersections, convey two T-intersections to four-leg intersection, close intersection leg.
• Indirect left-turn treatments:Jughandle, median U-turn crossover, continuous-flow intersection, quadrant roadway intersection, and super-street median crossover.
• Grade separation treatments: Split intersection and diamond interchange.

Approach Treatments:

• These treatments ensure that approaching motorists, bicyclists, or pedestrians can see that an intersection is ahead, and that a traffic signal is controlling the traffic flow. The following treatments are discussed in detail: Signal-head placement and visibility, signage and speed control treatments, roadway surface improvements, and sight distance treatments.

Individual Movement Treatments:

• These treatments influence how vehicles travel though signalized intersections and how they make left-, right-, and U-turns at these intersections. The following treatments are discussed: Left turn, through lane, right turn, and variable lane use.

See Key Results above.

None

U-Turns at Signalized Intersections (KTC-04-12/SPR258-03-3F)

Kentucky Transportation Cabinet
200 Mero Street
Frankfort, KY 40622

COTR:

Not Specified

Stamatiadis, N., Kala, T., Clayton, A., and Agent, K.

June 2004

30

None

Literature Review, Survey; Simulation

Normal

Not Specified

To examine the safety consequences from the installation of U-turns at signalized intersections in Kentucky and to develop a set of guidelines for using this alterative in the future.

A literature review was completed, followed by a safety study of the current applications and a simulation analysis for developing guidelines based on volumes and delays. A questionnaire was also administered at one of the Kentucky sites (Somerset) to determine the opinions of business owners related to the effect of the design on their business, as well as the safety impacts.

Kentucky Installations:

• Three signalized intersection sites where U-turns have been installed were examined (Somerset, Lexington, and Pikeville).
• Crash history for each site was examined to determine whether there were any safety consequences from the U-turn design.

Opinion Survey:

• A questionnaire was developed that was distributed to a large number of the businesses along the Somerset location.
• The questionnaire asked the respondents to identify their type of business and provide comments regarding the U-turn installation and perceived problems or benefits as a result of the new design.
• A total of 200 questionnaires were mailed and 73 responses were received.

Operational Guidelines:

• A simulation of a basic corridor was used.
• The corridor volume and the left- and U-turning volume percentages were varied to examine their influence on the operation of the corridor under both conditions.

U-Turns, Safety, Delays, Traffic Flow, Capacity

Literature Review:

• The most efficient configuration of a U-turn is that of a stop-controlled median U-turn. This has been shown to increase intersection capacity by 20 to 50 percent while decreasing the rate of crashes by up to 30 percent.
• Median openings placed only on the arterial also work well.

Opinion Survey:

• The survey found that there is a perception by about one-third of the businesses that there has been a negative economic impact, while about one-quarter felt that there was a positive effect on their business.
• The most common negative comment about safety dealt with drivers disregarding the red indication.

Operational Guidelines:

• The movements under the base condition experienced higher average delays than the corresponding movements under the U-turn condition. Statistical tests indicated that there was a statistically significant difference.

• The most efficient configuration is that of stop-controlled medium U-turns.
• An analysis of the crash data shows that the U-turn design in the Kentucky locations did not result in a large number of crashes involving U-turning vehicles.
• Also, at the Somerset location where the design eliminated median crossovers between intersections, there was a decrease in total crashes.
• Using delay time as a measure of effectiveness, it was concluded that the presence of the U-turn enhances the operation of the corridor most likely because of the more efficient processing of vehicles at the downstream intersection.
• The study recommends that U-turns should be considered for corridors with peak volumes greater than 1,500 veh/h or for cases where the expected total turn volume is greater than 20 percent of the total approach volume.

It is recommended that further research be conducted in this area, especially if it is desired to further refine the guidelines for future use of this design.

Intersection Negotiation Problems of Older Drivers, Volume I:
Final Technical Report

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Not Specified

Staplin, L., Gish, K.W., Decina, L.E., Lococo, K.H., and
McKnight, A.S.

September 1998

69

On-Road Study

Normal

Not Specified

To obtain valid field measures of older drivers’ difficulties when negotiating intersections, and to determine if their visual, mental, or physical abilities measured in an office could predict their performance behind the wheel.

Field observations of intersection negotiation were conducted using 82 subjects, age 61 and older (average age was 77). The subjects first completed a functional test battery measuring vision, attentional capabilities, and head/neck flexibility. They then underwent on-road testing administered by department of motor vehicles (DMV) examiners.

• Each subject completed a battery of functional measures to test vision, attention, and selected perceptual skills. Specifically, the functional abilities of the study sample measured by the test battery included static and dynamic visual acuity, static and dynamic visual contrast sensitivity, sensitivity to the relative motion of other vehicles slowing or stopping in the road ahead, divided attention (in a brake reaction situation), detection of pedestrian and vehicle targets in the visual periphery, skills attending to a central (foveal) task, and head/neck flexibility (degrees of rotation to both sides).
• Following completion of the functional test battery, all subjects performed test drives over a common standard route of relatively low familiarity. Unless terminated for safety reasons, the subject then completed a test drive over a high-familiarity route in his/her home area. On both routes, the subjects used their own vehicles, and were accompanied by a DMV examiner.
• During the on-road tests, a miniature, multiple-camera apparatus in the driver’s own vehicle recorded visual search behaviors, brake and accelerator use, and traffic events in the forward scene.

Driver, Safety, Mobility, Age, Intersection, Familiarity, Functional Impairment, Functional Testing, Road Test, Licensing, Screening, Vision, Attention, Maneuver Errors.

• Analysis of the videotaped data revealed a high incidence of visual search errors. Drivers failed to observe behind their vehicles before slowing down during the approach to an intersection 87 percent of the time on unfamiliar routes and 96 percent of the time on familiar routes. They also failed to scan to the sides after entering the intersection 75 percent of the time, on both route types. One type of maneuvering error, "infringing on others’ right of way when changing lanes," was also notable, occurring at a 90 percent rate on unfamiliar routes and a 57 percent rate on familiar routes.
• The highest error rate for an actual maneuver, as captured by the cameras, was making a lane change with an unsafe gap. This problem was exaggerated on the low-familiarity test route, where drivers had no expectation of where the next turn would occur.
• Analysis of errors recorded by the DMV examiners followed the same general pattern as the video-based error classification, where scanning errors predominated across both familiar and unfamiliar test routes, and maneuver errors occurred less frequently.
• Those driving errors observed most often by the examiners included failure to stop completely at a stop sign, stopping over a stop bar, improper turning path, and stopping for no reason.
• Regression analyses examined the relationships between functional test results and weighted examiners’ error scores. Speed of response on visual discrimination tasks was the best predictor; however, no single measure accounted for more than 18 percent of the variance on the criterion.

• Older drivers, like all drivers, seem to engage in many intersection negotiation behaviors that could be classified as driving errors, but which have little apparent bearing on safety. Therefore, research into the types of predictor-criterion relationships at issue here should focus specifically and exclusively on those errors that best predict crashes, consistent with the practices of licensing examiners.
• The present findings suggest that improvements in the safety of intersection negotiation by older drivers can be brought about through changes in engineering practice, such as increased use of signals. However, since this practice is likely to be cost-prohibitive at all but the highest crash sites, a suggested benefit of restricting certain high-risk older drivers to travel on familiar routes should be evaluated, under controlled studies wherever permissible.
• Practical limitation in the time, expense, and/or complexity of any assessment procedures considered for large-scale implementation among the older population suggest that the greatest contribution to improved safety may result from measures designed to identify only the most clear and profound levels of diminished functional capability.

This report is part of a two-volume report. Volume I presents the field study methodology and results. Volume II presents the background synthesis.

Intersection Geometric Design and Operational Guidelines for Older Drivers and Pedestrians, Volume III: Guidelines (FHWA-RD-96-137)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Elizabeth Alicandri

Staplin, L., Harkey, D.L., Lococo, K.H., and Tarawneh, M.S.

May 1997

64

None

Literature Review, Field Test

Normal

All

To develop guidelines for changes in the geometric design and operations at intersections with the greatest potential to aid in their use by older drivers and pedestrians.

A literature review identified age-related diminished capabilities that affect performance at intersections, and examined current design standards and their adequacy for older road users. A set of problem identification studies (crash database analysis, task analysis, focus group discussions, field observations) were conducted to better define older persons’ difficulties in intersection use, and an expert panel met to prioritize variables for more extensive laboratory and field studies ater in the project. These studies subsequently focused on age and the effects of opposite left-turn lane geometry, right-turn channelization and curb radius, and varying median pedestrian refuge island configurations, using both objective (performance) and subjective measures.

The following is the method for the parent study, upon which the recommendations in this report are based.

Laboratory Study:

• The laboratory study evaluated left-turn gap acceptance by drivers waiting in a left-turn storage bay to turn left across a stream of opposing traffic during the permissive signal phase.
• Four levels of offset left-turn lane geometry were studied: (1) 3.6-m (12-ft) "full positive" offset, (2) 1.8-m (6-ft) "partial positive" offset, (3) aligned (no offset), and (4) 1.8-m (6-ft) "partial negative" offset.
• Measures of effectiveness: Critical gap size, last safe moment to turn, frequency of unsafe gaps accepted, ratings of the perceived level of hazard.
• Seventy-two subjects participated in the study (24 were ages 25 to 45, 24 were ages 65 to 74, and 24 were age 75 or older).

Field Studies:

• Four levels of offset of opposite left-turn lane geometry were examined in the field: (1) 1.8-m (6-ft) "partial positive" offset, (2) aligned (no offset) left-turn lanes, (3) 0.91-m (3-ft) "partial negative" offset, and (4) 4.3-m (14-ft) "full negative" offset.
• All intersections were located on major or minor arterials within a growing urban area where the speed limit was 56 km/h (35 mi/h).
• Measures of effectiveness: Critical gap size, clearance time, left-turn conflict, longitudinal and lateral positioning, percentage of drivers positioning themselves within the intersection, site-specific intersection use survey, and general intersection safety survey.
• A total of 100 subjects were tested across the same three age groups used in the laboratory study.

Safety, Mobility, Age, Intersection, Design, Operations, Sight Distance, Channelization, Driver, Pedestrian, Critical Gap,
Left-Turn Lane Offset

Recommendations for Design:

• Unrestricted sight distances and corresponding left-turn lane offsets are recommended, whenever possible,in the design of opposite left-turn lanes at intersections.
• At intersections where there are large percentages of left-turning trucks, the offsets required to provide unrestricted sight distances for opposing left-turning trucks should be used.
• The following countermeasures are recommended to reduce the potential for wrong-way maneuvers by drivers turning left from the stop-controlled minor roadway:
  • Proper signage must be implemented.
  • Channelized left-turn lanes should contain white pavement lane-use arrows.
  • Pavement markings that scribe a path through the turn.
  • Use of a wide (61-cm) white stop bar at the end of the channelized left-turn lane.
  • Placement of 7.2-m wrong-way arrows in the through lanes.

Recommendations for Operational and Traffic Control Countermeasures:

• Where problems with sight-restricted geometries are intractable, the following are recommended:
  • Eliminate permissive left turns at intersections and implement only protected/prohibited left-turn operations where the sight distance falls significantly below the required minimum sight distance, and/or a pattern of permissive left-turn crashes occur.
  • Restrict permissive left turns to low-volume conditions (such as during nonrush hour).
  • Narrow the left-turn lanes to force the lateral position of drivers as close to the right edge as possible.
  • Add a lag-protected phase to clear out queued drivers.
  • Consider the use of intelligent signal phasing (such as gap-sensitive signal phasing).

• A critique of the data obtained in these studies during a second expert panel meeting concluded that sufficient evidence exists to support guidelines for: (1) geometric design to ensure a minimum required sight distance for drivers turning left from a major roadway, and (2) operational changes to accommodate older drivers where (re)design of an intersection to meet sight distance requirements is not feasible.
• A revision of case V in the AASHTO Green Book to determine sight distance requirements that reflect the perceptual task of gap judgment by a left-turning driver more accurately than the current assumptions in case IIIB is recommended.
• Further research needs to enhance the safety and mobility of older road users at intersections are identified.

This volume is the third in a series. The other volumes in the series are: Volume I: Final Report (FHWA-RD-96-132), and Volume II: Executive Summary (FHWA-RD-96-138).

Intersection Geometric Design and Operational Guidelines for
Older Drivers and Pedestrians, Volume I: Final Report
(FHWA-RD-96-132)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Elizabeth Alicandri

Staplin, L., Harkey, D.L., Lococo, K.H., and Tarawneh, M.S.

May 1997

249

None

Laboratory Study, Field Test

Normal

All

To develop guidelines for changes in the geometric design and operations at intersections with the greatest potential to aid in their use by older drivers and pedestrians.

A literature review identified age-related diminished capabilities that affect performance at intersections, and examined current design standards and their adequacy for older road users. A set of problem identification studies (crash database analysis, task analysis, focus group discussions, field observations) were conducted to better define older persons’ difficulties in intersection use, and an expert panel met to prioritize variables for more extensive laboratory and field studies later in the project.

Focus Group:

• Eighty-one older road users, assembled in 11 discussion groups, were recruited as paid study participants. Focus group discussions were conducted with 6 to 8 individuals at a time.
• The activity included the completion of an intake questionnaire addressing intersection use patterns, as well as more general information regarding driving history and exposure.

Laboratory Study:

• The laboratory study evaluated left-turn gap acceptance by drivers waiting in a left-turn storage bay to turn left across a stream of opposing traffic during the permissive signal phase.
• Four levels of offset left-turn lane geometry were studied: (1) 3.6-m (12-ft) "full positive" offset, (2) 1.8-m (6-ft) "partial positive" offset, (3) aligned (no offset), and (4) 1.8-m (6-ft) "partial negative" offset.
• Measures of effectiveness: Critical gap size, last safe moment to turn, frequency of unsafe gaps accepted, ratings of the perceived level of hazard.
• Seventy-two subjects participated in the study (24 were ages 25 to 45, 24 were ages 65 to 74, and 24 were age 75 or older).

Field Studies:

• Four levels of offset of opposite left-turn lane geometry were examined in the field: (1) 1.8-m (6-ft) "partial positive" offset, (2) aligned (no offset) left-turn lanes, (3) 0.91-m (3-ft) "partial negative" offset, and (4) 4.3-m (14-ft) "full negative" offset.
• All intersections were located on major or minor arterials within a growing urban area where the speed limit was 56 km/h (35 mi/h).
• Measures of effectiveness: Critical gap size, clearance time, left-turn conflict, longitudinal and lateral positioning,percentage of drivers positioning themselves within the intersection, site-specific intersection use survey, and general intersection safety survey.
• A total of 100 subjects were tested across the same three age groups used in the laboratory study.

Safety, Mobility, Age, Intersection, Design, Operations, Sight Distance, Channelization, Driver, Pedestrian, Critical Gap, Left-Turn Lane Offset

Focus Group Results:

• Almost everyone responded positively regarding the jughandle design. Overall, 76 percent of the group agreed that entirely eliminating left turns across busy roadways through the use of this design was a safe and convenient practice. However, 22 percent of this group qualified this statement with the fact that it was only a good idea if plenty of advance warning was given.
• Of the participants, 28 percent voiced a negative opinion about traffic circles.

Laboratory Study:

• Smaller critical gap sizes were found for the full positive geometry than for the partial positive, aligned, or partial negative geometries.
• Virtually equal "least safe gap" sizes were found across geometry, except for a sharp decrease in mean least safe gap size for the partial negative offset condition.
• Larger gaps were required in the presence of an oncoming truck compared to the gap size for an oncoming passenger car.
• The mean least safe gap size increased with increasing driver age.
• Significant three-way interactions were found between geometry, age, and oncoming vehicle type on mean least safety gap judgments, with the largest gap requirements for the age 75+ group with aligned geometry and trucks as the oncoming vehicle.
• Disproportionately higher percentages of unsafe gaps were accepted by the age 75+ group under the partial negative geometry, for both opposite left-turning vehicle types.

Field Study:

• Significant main effects of age and geometry on critical gap size were found, with longer critical gaps demonstrated for the age 75+ drivers and the -4.3-m opposite left-turn lane offset.
• A significant effect of geometry on lateral positioning and on longitudinal positioning was found, where the more negative the offset, the farther to the left and the closer drivers must move longitudinally to the center of the intersection to improve their visibility of through traffic.
• A significant effect of age and gender on vehicle positioning was found, where older drivers and female drivers were less likely to position themselves within the intersection to improve sight distance.
• Subjective responses to survey questions indicated that two-thirds of drivers feel that a green arrow is safer than a green ball, 8 out of 10 drivers feel that making a left turn on a green ball is safe at some locations and unsafe at others (underscoring the importance of geometric elements), and 9 out of 10 drivers feel that making a left turn on a green ball is the most stressful of all intersection maneuvers.

Future Research Priorities:

• Develop ecologically valid models of pedestrian crossing behavior at intersections.
• Identify and determine the relative importance of factors influencing driver gap decisions at intersections.
• Driver demand as a figure of merit for proposed highway engineering countermeasures.
• Implement and evaluate technologies for active traffic control at intersections.
• Implement and evaluate technologies for active pedestrian control at intersection.

None

Examination of Signalized Intersection, Straight Crossing-Path Crashes, and Potential IVHS Countermeasures (DOT-HS-808-143)

National Highway Traffic Safety
Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Not Specified

Tijerina, L., Chovan, J.D., Pierowicz, J., and Hendricks, D.L.

August 1994

60

http://www.its.dot.gov/itsweb/EDL_webpages/webpages/SearchPages/Alpha_Search.cfm

Crash/Demographic Statistical Analysis

Normal, Degraded, Imminent Crash (ICA)

Light Vehicles

To provide a preliminary analysis of signalized intersection, straight crossing-path (SI/SCP) crashes and applicable countermeasure concepts for the Intelligent Vehicle-Highway System (IVHS) program. The intent of the report is to identify crash avoidance opportunities and to illustrate design challenges for SI/SCP crash countermeasures.

• This report presents the results of a study of the SI/SCP type of collision as identified by the NHTSA Office of Crash Avoidance Research (OCAR).
• An in-depth analysis of SI/SCP crashes was conducted to identify crash circumstances and causal factors. The sample consisted of 37 reports from the 1992 Crashworthiness Data System (CDS) and 13 police accident reports (PARs) from the General Estimates System (GES) 1991 statistics.

• The SI/SCP crash was defined as a crash at a signalized intersection in which a subject vehicle (SV) with the right of way and a principal other vehicle (POV) collide in straight crossing paths.
• An analytic model of intersection negotiation behavior at signalized intersections was presented to indicate possible sources of driver actions that might contribute to such crashes.
• Crash avoidance system (CAS) concepts were developed to address each of the major causal factors identified in the data analysis.
• The report concluded with a discussion of research needs to support further refinement of the SI/SCP scenario and other crash avoidance concepts.

Vehicle Crash Analysis, Crash Countermeasures, IVHS, Kinematic Models, Crash Circumstances

Crash Characteristics and Causal Factors:

• SI/SCP crashes occur mostly under conditions of dry pavement (79 percent), good weather (66 percent), and daylight (72 percent), and involve predominantly people less than 54 years of age traveling over a wide range of velocities.
• SI/SCP crashes were mostly attributed to the following three factors: (1) driver unawareness because of inattention and obstructed vision, (2) failure to obey the red-light signal, and (3) driver attempted to beat the amber light signal (see figure).

CAS Countermeasure Concepts:

Three IVHS countermeasure concepts, specific to the SI/SCP crash scenario, were devised as follows to address the causal factors:

• In-vehicle alert: Indicates a signalized intersection ahead. Addresses factor 1 above.
• Driver warning: Graded warnings and constant warning times required to avoid the SI/SCP crash. Addresses factors 1 and 2 above.
• Control intervention: Automatically activated braking automation (soft braking, moderate braking, or graded braking, with or without driver override). Addresses factors 1, 2, and 3 above.

Figure A. Distribution of causal factors associated with SI/SCP crashes.

Research Needs:

• Clinical Analysis Area: Increase sample size in analysis, SI/SCP crashes resulting from loss of traction.
• Driver Behavior at Signalized Intersections: Higher order responses, correlation between driver reaction time and braking rate, correlation between brake reaction time and peak braking deceleration, driver decision processes, effects of fully automated control system (FACS) on the driver, interaction between drivers, alternative alert displays, driver interaction with warning systems.
• SI/SCP Algorithm Research Needs: Additional crash countermeasure concepts, impact of errors on system effectiveness, CAS set points, impact of velocity profiles on algorithm robustness.

Further Modeling Research Needs: Multiple vehicle interactions.

None

Crash Models for Rural Intersections: Four-Lane by Two-Lane Stop-Controlled and Two-Lane by Two-Lane Signalized (FHWA-RD-99-128)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Joe Bared

Vogt, A.

October 1999

182

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographics Statistical Analysis, Field Study

Normal

All

To assess the combined and relative effects of highway variables on intersection crashes for the following classes of intersection:

• Rural three-leg and four-leg intersections on four-lane highways, stop controlled on the minor legs.
• Signalized rural intersections of two-lane roads.

Data were acquired from the Highway Safety Information System (HSIS), State and Federal photologs, and field work at all intersections. The final data sets consisted of 84 three-leg intersections, 72 four-leg intersections, and 49 signalized intersections.

• Three classes of intersections were considered: (1) three-leg intersections with major-road four-lane and minor-leg two-lane stop controlled; (2) four-leg intersections with major-road four-lane and minor-leg two-lane stop controlled; and (3) signalized intersections with both two-lane major and minor roads.
• The field work included morning and evening traffic counts by movement and vehicle type, as well as alignment measurements out to 244 m (800 ft) along the major road.
• The chief classes of variables in this study are: Crash variables, traffic variables, intersection geometric variables, roadside variables, alignment variables, and sight distances. The intersection geometric variables concern medians, channelization, and intersection angle. Alignment variables and sight distance variables, which pertain to the roadway as far out as 244 m (800 ft) to several thousand feet from the intersection center, are treated separately.
• Negative binomial models were developed for each of the three data sets.
• Models were developed for all crashes within 76 m (250 ft) of the intersection center, for intersection-related crashes within 76 m (250 ft), and for injury crashes. Models of crashes at signalized intersections by approach flows were also investigated.

Highway Safety, Crash Prediction Models, Negative Binomial Regression, Intersection Design

• Significant variables included major- and minor-road traffic; peak major- and minor-road left-turning percentage; number of driveways; channelization; median widths; vertical alignment; and, in the case of the signalized intersections, the presence or absence of protected left-turn phases and peak truck percentage.
• For injury crashes, intersection angle and minor-road posted speed are significant.
• For the three-leg intersections, ADT explains 17 to 18 percent of the variation, while MEDWIDTH1 and NODRWYI explain another 4 to 5 percent. For the four-leg intersections, ADT explains 8 to 10 percent of the variation, while major-road left-turn percentage and/or the presence of a major-road left turn explains another 5 percent.
• In sharp contrast, for the signalized intersections, ADT by itself explains a negligible percentage of crashes.Turning and truck percentages explain 1 to 3 percent and the design variables PROT_LT and VEICOM explain 6 to 13 percent, depending on the model.

Note: Negative Accident Reduction Factors signify an increase in crashes.

• The data in this study have shortcomings. These include relatively small sample sizes, peak turning percentages and truck percentages measured by samples not contemporary with the crash data, and the difficulty of measuring and defining crash and intersection variables.
• In addition to the six main models, alternate models deserve consideration. These include variants given in the tables using other variables, the flow models in chapter 5, models that restrict the range of certain inputs (piecewise linear) or allow quadratic dependencies, and model forms suggested by Hauer.
• Major-road ADT plays a lesser role as one passes from three-leg to four-leg to signalized intersections, with turning percentage measures becoming more important and unexplained crash frequency variation increasing.
• The six main models adequately summarize the data in this study, with the choice of a crash variable TOTACC(all crashes within 76 m (250 ft)) or TOTACCI (all intersection-related crashes within 76 m (250 ft)) to be determined by other criteria.

None

Accident Models for Two-Lane Rural Roads: Segments and Intersections (FHWA-RD-98-133)

Office of Safety and Traffic
Operations Research and
Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Joe Bared

Vogt, A., and Bared, J.G.

October 1998

179

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

All

This report describes the collection, analysis, and modeling of crash and roadway data pertaining to segments and intersections on rural roads.

• Data were acquired from the Highway Safety Information System (HSIS), photologs, construction plans, and State databases for Minnesota (1985-1989) and Washington State (1993-1995).
• More than 1,300 segments and more than 700 intersections are included in the final samples on which the modeling is based.
• Models of Poisson type, negative binomial type, and extended negative binomial type (the latter by Shaw-Pin Miaou) were developed, and advanced statistical techniques were applied to assess the explanatory value of the models in the presence of Poisson randomness and overdispersion.

Data collected include:

These data are often estimates based on averages and are subject to some uncertainties in location and time. ADTs are based on observations at selected sites, interpolation, and/or extrapolation, and are particularly crude estimates in the case of intersections. In view of the importance of ADT in the modeling, the crudeness of these estimates should serve as a caution.

Highway Safety, Accident Prediction Models, Negative Binomial Regression, Extended Negative Binomial
Models, Highway Geometric Design

• The models derived from these data indicate that exposure and traffic counts are the chief highway variables contributing to crashes, but that surface and shoulder width, roadside conditions, and alignments are also significant, especially in the segment models
• In general, the Poisson, negative binomial, and extended negative binomial models give mutually consistent values for regression coefficients. The T1 statistic indicates that overdispersion is present and that negative binomial models are preferred.
• Most of the variables in the study are significant. The chief variables–exposure, lane and shoulder width, Roadside Hazard Rating and driveway density, and the alignment variables–are all represented.
• Differences appear between the Minnesota and Washington State models (for example, the insignificance of the Roadside Hazard Rating in the Minnesota segments, the anomalous sign of lane width in the Washington State segments, differences in the commercial traffic percentage variable T between the two States, and the insignificance of most of the variables on the Washington State three-leg intersections).
• These models yield the Accident Reduction Factors shown in the table below. Recall that the Accident Reduction Factor is the percentage decrease in mean predicted crash count when a variable is increased by one unit, all other variables being held fixed. A negative value signifies that crashes increase by that percentage when the variable is increased by one unit.

• Validation based on a chi-square statistic (), mean absolute deviation (MAD), and mean absolute scaled deviation (MASD) suggests that the models have some predictive power.
• Despite the incompleteness of the data and uncertainties in the values of some variables, the quantity, quality, and variety of the data give the models both descriptive and predictive value.
• Of great importance for the practical utility of models, such as the ones presented here, is the issue of how to adapt them to different States and regions and/or different time periods. A multiplier is needed that can be applied to a standard model to adjust it to a different State or region (for example, New England vs. the Great Plains) and/or a different period (1999 vs. 2001-2005) for circumstances in which drivers, vehicles, law enforcement, and demographics may differ from those under which the standard model was developed.

None

Intersection Crossing-Path Crashes: Problem Size Assessment and Statistical Description (DOT-HS-808-190)

National Highway Traffic Safety
Administration
Office of Collision Avoidance Research
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Not Specified

Wang, J.S., and Knipling, R.R.

August 1994

134

http://www.its.dot.gov/itsweb/EDL_webpages/webpages/SearchPages/Alpha_Search.cfm

Crash/Demographic Statistical Analysis

Imminent Crash (ICA)

All

To present a problem size assessment and statistical crash description for intersection crossing-path (ICP) crashes.

Data from the 1991 General Estimates System (GES) were analyzed for five vehicle type categories:

• All vehicles.
• Passenger vehicles.
• Combination-unit trucks.
• Medium/heavy single-unit trucks.
• Motorcycles.

• ICP crashes were classified into three subtypes: (1) signalized intersection perpendicular crossing path (SI/PCP), (2) unsignalized intersection perpendicular crossing path (UI/PCP), and (3) left turn across path (LTAP) subtypes.
• The ICP crash problem size was assessed using such measures as number of crashes, number and severity of injuries, crash involvement rate, and crash involvement likelihood.
• Descriptive statistics were provided for all vehicles only. ICP crashes and the three crash subtypes were described statistically primarily in terms of the conditions under which they occur (e.g., time of day, weather, roadway type, relation to junction) and in terms of possible contributing factors.

Traffic Accidents, Intersection Crossing-Path Crashes, Perpendicular Crossing-Path Crashes, Left Turn Across Path Crashes, Crash Avoidance Countermeasures, Combination-Unit Trucks, IVHS, Single-Unit Trucks,
Motorcycles, Traffic Crash Statistic

• In 1991, there were 1,803,000 ICP crashes, constituting 29.5 percent of all police-reported crashes (see figure below). The estimated number of non-police-reported ICP crashes was approximately 2,224,000.
• In these crashes, there were approximately 1,082,000 injuries, including 144,000 fatal or incapacitating injuries. ICP crashes caused approximately 26.7 percent of all crash-caused delay.
• In 1991, ICP crashes constituted 30.2 percent of passenger vehicle crashes, 17.4 percent of combination-unit crashes, 25.3 percent of single-unit truck crashes, and 31.0 percent of motorcycle crashes.
• Passenger vehicles were involved in 96.7 percent of all ICP vehicle crashes.
• Based on vehicle-miles of travel, motorcycles had the highest ICP involvement rate (351.2 per 100 million vehicle-miles traveled (VMT), compared to 173.8 for passenger vehicles, 61.5 for single-unit trucks, and 34.8 for combination-unit trucks).
• The following numbers of vehicles were involved in ICP crashes: 21.0 per 1,000 combination-unit trucks, 19.2 per 1,000 passenger vehicles, 7.8 per 1,000 single-unit trucks, and 7.7 per 1,000 motorcycles.
• The table below summarizes the sizes and proportions of the three ICP crash subtypes relative to the total number of all crashes.
• During weekends, more ICP crashes occur during nighttime hours; however, during weekdays, more crashes occur during morning and evening rush hours. Overall, about 26.0 percent of ICP crashes occurred during afternoon traffic hours compared with 13.2 percent occurring during morning traffic hours.
• For all known values for which the roadway type is known, about 72.0 percent of ICP crashes occurred on nondivided highways, 24.5 percent on divided highways, and 3.5 percent on one-way trafficways (unknown rate: 29.1 percent).
• 48.7 percent of ICP crashes occurred on one- or two-lane roadways, 36.8 percent on three- or four-lane roadways, and 14.5 percent on roadways with five or more lanes (unknown rate 25.9 percent).
• Overall, 96.8 percent of ICP crashes occurred on straight roadways, 78.5 percent occurred on level roadways, and 76 percent occurred on roadways that were both straight and level. Furthermore, 76.8 percent of ICP crashes occurred on dry roadways, 19.6 percent occurred on wet roadways, and 3.6 percent occurred on extreme surface conditions.
• ICP crash involvement rates per 100 million VMT were highest for younger driver, next highest for older drivers, and lowest for middle-aged drivers. Overall, females had the highest involvement rate.
• The most common violations charged were failure to yield, running a traffic light, and impairment by alcohol/drugs.

Figure A. Intersection crossing-path crashes.

See Key Results above.

None

Restoring Credibility to Speed Setting: Engineering, Enforcement, and Educational Issues (Speed Management Workshops)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Anonymous

2000

7

http://safety.fhwa.dot.gov/speed_manage/docs/workshopreport.pdf

Workshop

Normal

Not Specified

As part of an approach to address the problem of speeding, the U.S. DOT Speed Management Team joined with the Intelligent Transportation Society of America to sponsor two speed management workshops. The objective of the workshops was to identify actions needed to restore the credibility of speed limits across the Nation.

The first workshop was held in January 2000, in conjunction with the Transportation Research Board (TRB) annual meeting in Washington, DC. The second workshop was held in March 2000, in Dallas, TX.

Workshop participants addressed the following issues:

• Methodologies used for setting realistic speed limits.
• Public perception and acceptance of speed limits and enforcement efforts.
• Existing and new speed-setting and enforcement technologies.
• Engineering and operations concerns.
• Judicial considerations.
• Lessons learned through domestic and foreign experiences in speed management.

Speed Management, Engineering, Enforcement, Education, Speed Setting

Engineering Issues:

• Participants at the workshops concurred on the need to improve cooperation between engineering and law enforcement personnel to set realistic, enforceable speed limits that are appropriate to roadway design.
• Participants felt that it was important to review, evaluate, and update speed limits periodically to accommodate changing demographics and increasing urbanization of previously rural areas.
• The following is a list of other issues addressed in the breakout sessions: Designing roadways with adequate infrastructure to accommodate law enforcement operations, monitoring speeds on roadways more effectively, incorporating new technologies to alert drivers to safety problems, developing standards for implementing variable speed limits, and increasing public education about the meaning and use of enforcement in construction work zones.

Enforcement Issues:

• Workshop participants at both sessions raised the issue of credibility in enforcing reasonable speed limits.
• They noted the crucial need for automated enforcement technology.
• Both sessions identified the importance of consistent and uniform enforcement of speed limits nationwide.
• The following is a list of other issues addressed in the breakout sessions: Reinforcing the quality, consistency, and accountability of speed limit enforcement; appropriating sufficient resources (personnel and technology) for speed limit enforcement; establishing reciprocity between jurisdictions; basing enforcement on what contributes to crashes; identifying safety as a paramount rationale for enforcement; establishing incentives for obeying speed limits; and using technology to keep drivers better informed about road conditions and incidents.

Judicial Issues:

• Improving cooperation between agencies and disciplines was raised as a critical issue.
• Participants also discussed the need for uniform consequences for reasonable enforcement of realistic speed limits, and increasing involvement and education among the agencies involved in establishing, enforcing, and adjudicating problems of speeding.
• The following is a list of other issues addressed in breakout sessions: Improving communication and training, reducing public tolerance for speeding, informing courts about where and why speed limits are updated, encouraging consistent and fair punishment for speeding violations, and seeking input from judicial officials on what they expect with regard to speed limits.

Political and Public Policy Issues:

• Education and cooperation were paramount concerns to workshop participants.
• They felt that there is a need for ongoing communication to educate politicians and policymakers about the rational setting, enforcing, and adjudicating of realistic speed limits.
• The following is a list of other issues addressed: Involving political officials in the process of setting speed limits; educating legislators on the benefits and uses of enforcement technologies; encouraging equal and consistent application of speed limits, enforcement, and adjudication across States; establishing and using reciprocity agreements among jurisdictions; changing speed laws from basic to absolute; educating the public, politicians, and policymakers about how aggressive enforcement improves traffic safety and quality of life.

• The results of the speed management workshops emphasize the need for enhanced communication and cooperation among the engineering, enforcement, judicial, and political partners who directly affect safety on the Nation’s roads.

None

Traffic Calming, Auto-Restricted Zones, and Other Traffic Management Techniques: Their Effects on Bicycling and Pedestrians (FHWA-PD-93-028)

Federal Highway Administration
400 Seventh Street, S.W.
Washington, DC 20590

COTR:

Not Specified

Clark, A., and Dornfeld, M.J.

1994

75

http://www.bikewalk.org/technical_assistance/case_studies.htm

Case Study

Normal

Not Specified

To examine the development of traffic calming in Europe and the United States, with a particular emphasis on the impact of such traffic management on bicyclists and pedestrians.

This report examines the development of traffic calming in Europe and the United States, with particular emphasis on the impact of such traffic management on bicyclists and pedestrians.

The body of the report can be divided into three parts:

• The first two major sections examine the history and traffic-calming techniques, respectively, installed in Europe, Japan, and the United States.
• The final section of the report examines the practical and policy implications of traffic calming.

Traffic Calming, Auto-Restricted Zones, Speed Management, Traffic Management

Traffic Calming in the United States:

• Traffic calming attempts in the United States tend to focus on spot locations and most have resulted in lower motor vehicle speed and fewer motor vehicle crashes.
• The following are a sample of traffic-calming techniques used in the United States: Speed hump installations, traffic circles (miniroundabouts), chicanes, bicycle boulevard, channelization changes, slow streets, transit street and pedestrian zones, signage techniques, traffic diverters, and corner radii treatments.
• In general, acceptance of traffic calming is high. Local residents felt that the benefits of traffic calming outweighed any minor inconveniences.
• There is little information on the effects of traffic calming on bicycle and pedestrian use. However, evaluations of the Palo Alto, CA, bicycle boulevard and Seattle, WA, channelization changes showed increases in the amount of bicycle traffic.

Benefits to Bicyclists and Pedestrians:

• The experience from Europe shows that bicycle use has been encouraged by traffic calming and that walking has been made much more attractive and levels of activity have increased in residential and shopping streets that have been calmed.
• Safety for children playing in their neighborhoods is improved by reducing the speeds of motor vehicles and can be accomplished by traffic calming.

Costs and Benefits of Traffic Calming:

• In the United States, the costs of failing to address excessive traffic and motor vehicle dependency are escalating. Traffic crashes alone cost the Nation up to $137 billion a year in direct costs, lost time, and productivity. Congestion is also costly.
• Lower and more consistent speeds improve the capacity of roadways, and the dedicated spaces typically provided for walking, bicycling, and transit can achieve shifts in modal choice toward these more efficient modes.

• Well-designed and implemented traffic-calming techniques can have a number of beneficial impacts for bicyclists and pedestrians. The reduced vehicle speeds associated with such projects can reduce both the severity and incidences of motor vehicle/bicycle/pedestrian crashes and can make bicyclists and pedestrians feel more comfortable in traffic.
• Traffic calming may be a more cost-effective and practical means of encouraging bicycling and walking than the development of separate networks of trails and multiuse paths.
• Traffic calming has been used to create more livable neighborhoods; vibrant automobile-free shopping streets; and pleasant, convenient bicycle routes.
• Traffic planners and engineers in the United States are realizing that traffic calming must be approached on an areawide basis.

There is a need for more research in the United States on the effects that traffic calming has on bicycle and pedestrian use.

FHWA International Technology Scanning Program: Summary Report of the FHWA Study Tour for Speed Management and Enforcement Technology (FHWA-PL-96-006)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Coleman, J.A., Cotton, R.D., Parker, M.R., Covey, R., Pena, H.E., Jr., Graham, D., Robinson, M.L., McCauley, J., Taylor, W.C., and Morford, G.

December 1995

69

http://ntl.bts.gov/DOCS/speed06.html

Informational Report

Normal

All

To document the findings of a study team from the United States that conducted a scanning tour in the Netherlands, Germany, Sweden, and Australia. The purpose of the tour was to obtain firsthand knowledge about the practices and policies concerning speed management and enforcement technology.

A brief overview of the speed management and enforcement policies, as well as individual speed-related projects that were reviewed are presented for each country visited. General conclusions are given based on the findings from all countries visited.

• The Transportation Technology Evaluation Center (TTEC) of Loyola College in Maryland planned and coordinated the study tour.
• The study team, consisting of 11 members, represented a cross section of Federal, State, and local highway agencies, enforcement officials, and researchers involved in speed management.
• Prior to conducting the scanning tour, the team prepared a comprehensive list of questions concerning speed management and enforcement technologies.
• During the period from April 21 through May 5, 1995, the scanning team visited the Netherlands, Germany, Sweden, and Australia.
• In each country, the team met with Federal, regional, and local transportation officials; law enforcement officers; researchers; communications experts; educators; consultants; and contractors.
• The team also made field trips to locations where speed management techniques and/or automated enforcement technologies were implemented.

Speed Limits, Speed Control, Law Enforcement, Study Tours, Traffic Calming, Radar, Laser Radar, Red-Light Running, Cameras, VASCAR, Photo Radar, Speed Management

For a speed management program to be successful, the following components are essential:

• The speed-related safety problem must be clearly identified and effectively communicated to everyone involved, especially the public.
• The strategy methods selected for implementation must have the potential for solving the problem.
• Engineering, enforcement, and educational speed management techniques must be integrated and coordinated.
• The plan must be fair and reasonable to the majority of road users.
• Implementation must be augmented with a continuous ongoing evaluation program to monitor and determine the effectiveness of the management techniques.
• The plan must be flexible and change when safety conditions merit.
• The road safety community must work with legislators to ensure that the necessary legislation is enacted and revised, as needed, to accomplish the speed management goals.
• Through each phase of the program, all participants must be kept informed and involved.

Major components of the plan should include:

• Long-term framework: Public education through extensive advertising to address beliefs and attitudes and to provide a rational basis to encourage that change is essential.
• Medium-term reviews: Examination and rationalization of the process, procedures, and practices.
• Short-term initiatives: Special targeted enforcement activity, with appropriate warnings, is necessary to reinforce particular safety issues.

The following are specific speed management methods:

• Realistic speed limits: The relationship between speed limits and the roadway environment must be credible and consistent.
• Variable speed limits: Because of the cost, variable speed limit systems should be implemented in areas where environmental and/or traffic conditions result in significant fluctuations in the desired speed.
• Speed governors on heavy vehicles: It is likely that there would be little political resistance if top speeds for heavy vehicles were limited to 113 km/h (70 mi/h).
• Traffic-calming techniques: Speed humps, roundabouts, lane narrowing, and other traffic-calming methods were employed to reduce vehicle speeds in residential areas in the countries visited.
• Speed limits based on driver perception: Additional research is suggested before implementation of these techniques.
• Public education/information: Examples include using music and sports figures to relay safety concepts to teenagers and introducing traffic safety curriculums into secondary schools.
• Enforcement technology: Specific enforcement technology and deployment methodologies that may be applicable in the United States are listed below:
  • VASCAR (Visual Average Speed Computer and Recorder).
  • Radar (RAdio Distance and Ranging).
  • Lidar (LIght Distance and Ranging).
  • Photo radar.
  • Red-light cameras.

See Key Results above.

None

Traffic Calming: State of the Practice (FHWA-RD-99-135)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Ewing, R.

1999

245

http://www.ite.org/traffic/tcstate.htm

Literature Review, Survey

Normal

Not Specified

To provide a synthesis of traffic-calming experiences to date in the United States and Canada.

This report draws from detailed information collected on traffic-calming programs in 20 featured communities, another 30 communities surveyed less extensively, and a parallel Canadian effort by the Canadian Institute of Transportation Engineers (CITE) and the Transportation Association of Canada (TAC). The intended audience is transportation professionals.

This report is broken down into the following sections:

• Brief history of traffic calming.
• Toolbox of traffic-calming measures.
• Engineering and aesthetic issues.
• Traffic-calming impacts.
• Legal authority and liability.
• Emergency response and other agency concerns.
• Warrants, project selection procedures, and public involvement.
• Beyond residential traffic calming.
• Traffic calming in new developments.

Traffic Calming, Speed Reduction, Pedestrian Safety

Brief History of Traffic Calming:

• Several trends are evident in Europe and Australia, such as the shift from volume controls to speed controls, from simple to diverse programs, and from spot to areawide treatments.
• The following are lessons learned from the implementation of traffic calming in Seattle, WA: Test complex areawide treatments before implementing them permanently, assess public support, conduct before/after studies of traffic impacts, include traffic crashes among the impacts studied, work with emergency services, and opt for the most conservative design.

Toolbox of Traffic-Calming Measures:

• Volume control measures: The primary purpose is to discourage or eliminate through traffic. The following are examples: Full- and half-street closures, diverters of various types (semi-diverters and diagonal diverters), median barriers, and forced turn islands.
• Speed control measures: The primary purpose is to slow traffic. The following are speed control measures: Speed humps, speed tables, raised intersections, textured pavement, traffic circles, chicanes, chokers, lateral shifts, and realigned intersections.
• Important trends: The following trends in the design and application of traffic-calming measures are discussed and should be considered in future practice: Simple to diverse programs, from volume to speed controls, from random to predictable treatments, from narrowing to deflection, spacing of measures, and from spot to areawide treatments.

Engineering and Aesthetic Issues:

• Horizontal curvature vs. vehicle speed: The sharper the horizontal curvature at a circle, chicane, or other slow point, the slower motorists will travel around or through it.
• Vertical curvature vs. vehicle speed: Vertical curves produce forces of acceleration that are uncomfortable for drivers exceeding given operating speeds. The sharper the vertical curvature at speed humps, speed tables, and other slowpoints, the slower motorists will travel over them.

Traffic-Calming Impacts:

• Traffic speeds: Speed humps have the greatest impact on 85^th percentile speeds, reducing them by an average of more than 11.3 km/h (7 mi/h), or 20 percent. Raised intersections, long speed tables, and circles have the least impact.
• Traffic volumes: The impact of traffic-calming measures on traffic volumes depends on the availability and quality of alternative routes.
• Collisions: The Insurance Corporation of British Columbia published a report titled Safety Benefits of Traffic Calming, which summarized 43 international studies. Among the 43 studies, collision frequencies declined by anywhere from 8 to 100 percent (see figure). In this particular survey, traffic circles and chicanes had the most favorable impacts on safety, reducing collision frequency by an average of 82 percent.

Emergency Response and Other Agency Concerns:

• The following are strategies for addressing emergency response concerns: Avoid emergency response routes, avoid emergency response facilities, gradually build traffic-calming measures, communicate, and use measures that accommodate fire and rescue vehicles.

Figure A. Reduction in collision frequency for all researched case studies.

See Key Results above.

None

Effects of Raising and Lowering Speed Limits on Selected Roadway Sections (FHWA-RD-92-084)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Howard H. Bissell
Davey L. Warren

Federal Highway Administration

1996

84

http://www.ibiblio.org/rdu/sl-irrel.html

Crash/Demographic Statistical Analysis

Normal

Not Specified

To determine the effects of changing speed limits on traffic operations and safety for surface (nonfreeway) rural and urban roadways.

Speed and crash data were collected in 22 States at 100 sites before and after speed limits were altered. Before/after data were also collected simultaneously at comparison sites where speed limits were not changed to control for the time trends.

Data Collection:

• The speed limits were lowered at 59 sites and raised at 41 sites. The sites included 63 rural sites, 22 small urban sites, and 15 urban sites. The section lengths varied from 0.5 to 20.3 km (0.3 to 12.6 mi).
• Traffic data were collected before and after the speed limits were changed for 24-hour (h) periods using automated roadside units connected to inductive loop mats to record speeds, headways, and types of vehicles. Data were collected for more than 1.6 million vehicles.
• Crash data included more than 6,000 reported crashes. For most sections, crash data were collected for a 3-year period before and a 2-year period after the speed limits were changed. Data were coded for crash type, severity, and light and surface conditions.

Data Analysis:

• Free-flow speeds (vehicles with headways of 4 s or greater) were used for the speed analyses. Mean speed, standard deviation of the speed distribution, percentile speeds, and percentage of vehicles exceeding the posted speed limits by 8, 16, 24, and 32 km/h (5, 10, 15, and 20 mi/h) were computed for all sites.
• Comparisons were made for groups of sites where speed limits were lowered by 8, 16, and 24 km/h (5, 10,and 15 mi/h).
• The analyses included a check for comparability, paired comparison ratios, cross-product ratios, an Empirical Bayes method, and the weighted average logit method. Because of the small sample sizes, the main analyses combined all sites where the speed limits were raised and all sites where they were lowered.

Speed Limits, Roads, Traffic Accidents

• Neither raising nor lowering the speed limit had much effect on vehicle speeds (mean speeds and the 85^th percentile speeds did not change more than 1.6 or 3.2 km/h (1 or 2 mi/h)), even for speed limit changes based on the amount that the posted speed limit was altered.
• The percentage of compliance with the posted speed limits improved when the speed limits were raised. When the speed limits were lowered, compliance decreased.
• Lowering the speed limit below the 85^th percentile or raising the limit to the 85^th percentile speed also had little effect on drivers’ speeds (see figure).

Figure A. Maximum and average changes in the 85^th percentile speeds at the experimental sites.

1 mi/h = 1.61 km/h

• Although changes in vehicle speeds were small, driver violations of the speed limits increased when the posted speed limits were lowered. Conversely, violations decreased when limits were raised.
• Based on the sites selected for this study, it appears that highway agencies have a tendency to set speed limits slightly below the average speed of traffic.
• Changing posted speed limits alone, without additional enforcement, educational programs, or other engineering measures, has only a minor effect on driver behavior.
• There is not sufficient evidence in this data set to reject the hypothesis that crash experience changed when posted speed limits were either raised or lowered.

Attention should be given to identifying factors or a method that leads to establishing uniform speed limits for similar roadway and traffic conditions.

Synthesis of Studies on Speed and Safety

(Transportation Research Record 1779, pp. 86-92)

School of Civil and Environmental
Engineering
Georgia Institute of Technology
Atlanta, GA 30318 300 Home Park Avenue, N.W.

COTR:

Not Specified

Feng, C.

2001

7

None

Literature Review

Normal

Not Specified

To present an overview of research interest in the United States and elsewhere on the relationship between speed and safety.

Studies on the relationship between speed and safety were compiled and reviewed. This paper tries to present a complete picture of these studies so that further exploration of the relationship can be based on solid ground.

Previous research is discussed for the following topics:

• Factors affecting safety.
• Factors affecting speed.
• Speed management.

Safety, Speed Management, Traffic Calming

Selected studies are reported for each topic below. The report gives a detailed review of several studies for each topic.

Factors Affecting Safety:

• Environment: These factors affect safety by impairing visibility, decreasing stability, and reducing controllability.Precipitation, fog, sunshine, and dust storms are possible causes of impaired visibility. Rain, snow, and ice can make road surfaces slippery and decrease vehicle stability. Simulation studies indicated that a sudden visibility reduction showed that traffic safety is decreased. However, drivers may compensate for a higher crash risk by reducing speeds,maintaining safe spacing, and driving more carefully.
• Distraction: Actions falling into this category are driving while talking, tuning the radio, looking for directions, using a cellphone, drinking, eating, smoking, and exercising curiosity.
• Speed limit: The speed of vehicles has shown an upward trend over the last 20 years; overall crash rates showed a steady decline. However, the fatality rate on the rural Interstate system has shown a 36 percent increase since the 105-km/h (65-mi/h) speed limit went into effect in 1987.
• Speed: NHTSA estimates that speed plays a role in 31 percent of all fatal crashes. Increases in travel speeds lead to a dramatic increase in collision severity.

Factors Affecting Speed:

• Environment: These factors affect not only mean speed, but also speed variance, because of the difference in driver experiences and characteristics. Some studies indicate that the standard deviation of speed doubles during fog events and triples during snow. Another study examined how various driver groups differ in their perception and adjustments.Survey results suggested that most drivers recognize the seriousness of the traffic safety problem and, in fact, had a fairly accurate impression of the relative risk associated with various driving conditions. However, the range of driver adjustments invoked during inclement weather did not reflect the magnitude of the weather hazard. The results suggested that countermeasure programs should focus either on improved skills training or on ways to induce greater caution during inclement conditions.
• Advisory and regulatory information: One study investigated the effects of route guidance systems on attentional demand and efficiency of the driving task. The results indicate that for long distances, no significant differences in speed and standard deviation of speed existed. However, for shorter distances, significant changes in speeds were identified. These findings suggested that drivers compensate by driving faster after a period of slowing in response to advisory information.

Speed Management:

• Variable speed limit: Previous research indicates that the benefits of variable speed limits were increased traffic throughput and improved safety.
• Camera: The results from one study indicate that: (1) speeding decreased at all sites, but the decreases were greater attest sites where photo radar was used; (2) the greatest decreases in the proportion of speeding vehicles at all sites were for vehicles traveling at the highest rates of speed; (3) media coverage of the use of photo radar affected the behavior of drivers at all sites; (4) the greatest speed reductions occurred on the six-lane test section; (5) the presence of signage announcing photo radar reduced speeding; and (6) an increase in enforcement presence and fully deployed photo radar units reduced speeding on the test roadways even more.
• Traffic-calming techniques: Previous research has concluded that using traffic-calming techniques can have positive effects on traffic safety, risk perception, and the environmental quality of the area.

• Most studies are site and time specific, so their results may not be true when generalized. To analyze the relationship between speed and safety in the long run, studies need to be carried out constantly and systematically.
• The speed limit must reflect real-time road, traffic, and weather conditions. A speed-limit calculation should be based on traffic flow prediction, prevailing speed, and environmental factors, so that the limit will be accepted by most drivers. This calls for variable speed limits.
• Studies found that drivers may not always accurately rate their driving behavior. This finding reminds one not to rely too heavily on data obtained by subjective methods.
• Recent studies showed strong interests in weather, and weather is found to have a close relationship with speed and safety. The impact of weather may include reduced visibility, stability,and controllability.

None

Design Factors That Affect Driver Speed on Suburban Arterials(FHWA/TX-00/1769-3)

Research and Technology Transfer
Section, Construction Division
Texas Department of Transportation
P.O. Box 5080
Austin, TX 78763-5080

COTR:

Not Specified

Fitzpatrick, K., Carlson, P.J., Wooldridge, M.D., and Brewer, M.A.

June 2000

160

None

Field Test

Normal

Not Specified

• Identify those factors that affect speed on suburban arterials and determine the range of the influence.
• This research project will help answer the following questions:
  • Do roadway variables affect speed on suburban arterials?
  • Which alignment, cross section, roadside, or traffic control device variables affect operating speed?
  • For a variable that affects speed, what is the design value range that is influential?

The project was subdivided into two phases. Phase I investigated potential data collection techniques, preliminary analysis techniques, and experimental designs. The lessons learned from the pilot studies conducted in phase I were used to develop the data collection methodology for phase II of the project.

Phase I :

• Laser Pilot Study: Laser guns were used to collect the speed of free-flowing vehicles as they approached, traversed, and departed the study site. Three laser guns were employed at six study sites to obtain a comprehensive speed profile for the horizontal curve and its approaches. The laser guns were wired to laptop computers that recorded data three times per second when the gun was activated.
• Individual Driver Pilot Study: Individual drivers drove an instrumented test vehicle. Six drivers drove through several arterial sections while their speeds and positions on the roadway network were monitored.

Phase II:

• The data collection and reduction methodology used was similar to the methodology used in the pilot effort. Laser guns were used to collect the speed of free-flowing vehicles through the study sites.

Operating Speed, 85^th Percentile Speed, Posted Speed Limit, Suburban Arterials, Curves, Straight Sections

• When all variables were considered, the only significant variable for straight sections was posted speed limit (see table below).
• In addition to posted speed, deflection angle and access density classes influence speed on curve sections.
• Without speed limit, only lane width is a significant variable for straight sections.
• For curve sites without speed limit, the impact of median presence now becomes significant along with roadside development.

• Using speed profiles, researchers were able to verify that the midpoint of a horizontal curve is where speeds are most influenced. This should help other researchers collecting data using spot speed methods.
• A finding from this project is that the way a curve appears to a driver may have an effect on the speed a driver selects prior to and within the beginning of a horizontal curve. Additional research is needed to develop a better understanding of how the appearance of the curve affects speed.
• While individual variables have an influence on speeds, the combination of several variables may also form an environment that has a significant influence on drivers. Limited access points, wide medians, unnarrowed lanes, few trees along the roadside, and other characteristics in combination encourage the higher speeds. Therefore, additional research could examine what combination of variables and their dimensions would encourage speeds within a given range.
• The operations at traffic signals can have a very significant impact on the speeds along a suburban arterial. In addition, the amount of traffic on the roadway can also result in decreased travel speeds. The influences of these variables were minimized in this study by selecting sites away from signals. Another study could include consideration of these other, highly influential variables on driver speeds on suburban arterials.

None

Speed Prediction for Two-Lane Rural Highways (FHWA-RD-99-171)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Ann Do

Fitzpatrick, K., Elefteriadou, L., Harwood, D.W., Collins, J.M., McFadden, F., Anderson, I.B., Krammes, R.A., Irizarry, N., Parma, K.D., Bauer, K.M., and Passetti, K.

August 2000

217

http://www.tfhrc.gov/safety/ihsdm/libweb.htm

Crash/Demographic Statistical Analysis

Normal

Light Vehicles, Commercial Vehicles

To develop speed-prediction equations for horizontal and vertical alignments and for other vehicle types, determine the effects of spiral transitions on speeds, determine the deceleration and acceleration rates for vehicles approaching and departing horizontal curves, validate the speed-prediction equations, develop a speedprofile model for inclusion in the Interactive Highway Safety Design Model (IHSDM), and identify the relationship of the design consistency module to other modules and components of the IHSDM.

• Speed and geometry data were collected from 176 sites distributed across 6 States (Minnesota, New York,Pennsylvania, Oregon, Washington, and Texas). Regression models were developed to predict the 85^thpercentile speed of passenger vehicles on horizontal curves, vertical curves, and combined horizontal and vertical curves based only on the geometry of the curves.
• Three possible ways in which combined horizontal and vertical alignments affect operating speeds were identified. Regression analysis was used to determine which alternative best describes how geometry influences the speeds of passenger cars.
• Regression analyses were also performed to determine if the presence of spiral transitions influenced the speed of passenger car drivers. In addition to evaluating passenger car speeds, the speeds of trucks and recreational vehicles were examined.

Independent Variables:

• Horizontal curve (degree of curvature, deflection angle, radius, length, grade, milepoint or station at the beginning of the curve).
• Vertical curve (approach grade, departure grade, length, milepoint or station at the beginning of the curve, point of intersection, end of curve, crest or sag, approach tangent length, approach tangent grade).
• Pavement geometry (pavement width, lane width, unpaved shoulder width, superelevation rate).

Dependent Variables:

• 85^th percentile speed.

Two-Lane Rural Highway, Speed-Prediction Equations, Acceleration/Deceleration, IHSDM

• A speed-profile model was developed that can be used to evaluate the design consistency of a facility or to generate a speed profile along an alignment. The design consistency evaluation consists of identifying undesirable speed changes between features. The speed-prediction equations are used to predict the speeds for the features, and then the differences in speed between successive features would be calculated.
• The speed-profile model developed in the research appears to provide a suitable basis for the IHSDM design consistency module.
• There is no difference in 85^th percentile speeds at the midpoint on circular curves from those with spiral transitions.
• The data for all truck types and recreational vehicles on horizontal curves display a general speed behavior that is similar to that of passenger vehicles.
• Of the candidate design consistency measures, four have relationships to crash frequency that are statistically significant and appear to be sensitive enough that they may be potentially useful in a designconsistency methodology. These four candidate design consistency measures are: (1) predicted speed reduction by motorists on a horizontal curve relative to the preceding curve or tangent, (2) ratio of an individual curve radius to the average radius for the roadway section as a whole, (3) average rate of vertical curvature on a roadway section, and (4) average radius of curvature on a roadway section. Of these candidate design consistency measures, the speed reduction on a horizontal curve relative to the preceding curve or tangent clearly has the strongest and most sensitive relationship to crash frequency.

• Of the different alternatives examined, a design consistency methodology based on predicted speed reductions was the best identified.
• Additional insight into the influences of speeds on tangent sections of various lengths and grades is needed.This would greatly enhance the effectiveness of any speed-profile model because it would validate the assumptions currently being made.
• Further research should be conducted to extend all aspects of this research, such as speed-prediction equations, acceleration/deceleration behavior, and the design consistency module speed-profile model, to roadway types other than two-lane rural highways.
• The IHSDM should contain a design consistency module based on the speed-profile model developed in this research. Further refinements should be made to the IHSDM design consistency module in future research to include the capability of identifying design inconsistencies based on factors other than horizontal and vertical alignment. Such factors might include intersections, driveways, and auxiliary lanes.
• Because the safety evaluation demonstrated that predicted speed reduction has the strongest relationship to crash frequency, speed reduction should be the primary measure in design consistency methodology for horizontal and vertical curvature.

None

Effectiveness of Changeable Message Signs in Controlling Vehicle Speeds in Work Zones (FHWA/VA-95-R4)

Virginia Department of Transportation
1401 E. Broad Street
Richmond, VA 23219

COTR:

Not Specified

Garber, N.J., and Patel, S.T.

August 1994

97

http://ntl.bts.gov/DOCS/EC.html

Field Test

Degraded

Not Specified

To evaluate the effectiveness of the changeable message sign (CMS) with radar unit in reducing work-zone speeds.

Four CMS messages designed to warn drivers that their speed exceeded the maximum safe speed were tested at seven work zones on two interstate highways in Virginia.

• Speed and volume data for the whole population traveling through the work zone were collected with automatic traffic counters.
• To assess the effect of CMS on high-speed drivers in particular, vehicles that triggered the radar-activated display were videotaped as they passed through the work zone.
• Using the data obtained from the traffic counters and videotapes, speed characteristics were determined at the beginning, middle, and end of the work zone.
• Those characteristics were computed for the entire population and for high-speed vehicles separately.
• The following four CMS were used: "You are speeding slow down," "High speed slow down," "Reduce speed in work zone," and "Excessive speed slow down."

Work Zones, Speed Reduction, Changeable Message Signs, Video Taping

• The odds ratios indicated that CMS effectively reduced the number of vehicles speeding by any amount, by 8.0 km/h (5 mi/h) or more, and by 16.1 km/h (10 mi/h) or more in the work zone. Approximately three-quarters of the odds ratios calculated represented a potential reduction of 70 percent or greater in the number of vehicles speeding if CMS were used in the work zones.
• An analysis of variance (ANOVA) used to compare speeds when using the CMS with speeds when using MUTCD signage only showed that all speed characteristics–average speeds, 85^th percentile speeds, speed variance, and the percentage of vehicles speeding by any amount, by 8.0 km/h (5 mi/h) or more, and by 16.1 km/h (10 mi/h) or more–were reduced by any of the four CMS messages. In some cases, these reductions were not significant.
• Trends in average and 85^th percentile speeds observed from the camera data show that all of the messages were effective in reducing the speeds of high-speed vehicles through the work zone (see figure).
• Finally, t-tests were conducted using the speed data obtained for the high-speed vehicles, and all of the messages were effective in significantly reducing the average speeds of those vehicles traveling 94.9 km/h (59 mi/h) or faster in an 88.5-km/h (55-mi/h) work zone when compared to MUTCD signage only.

Figure A. Average speeds (mi/h), camera data (I-81 South Buffalo Gap) (threshold speed limit: 94.9 km/h (59 mi/h), posted speed limit: 88.5 km/h (55 mi/h)).

1 mi/h = 1.61 km/h

• CMS with a radar unit are more effective than static MUTCD signs in altering driver behavior in work zones. Using personalized messages for high-speed drivers will result in these drivers being more inclined to reduce vehicle speeds in work zones.
• All of the messages on the CMS reduce the odds of speeding in the work zone. In most cases, the use of the CMS resulted in the reduction of vehicles speeding by 50 percent or more.
• There were no significant differences between the four messages. However, based on the behavior of the entire population, the messages were ranked in the following order of effectiveness: (1) "You are speeding slow down," (2) "High speed slow down," (3) "Reduce speed in work zone," and (4) "Excessive speed slow down."
• The following guidelines are suggested for the use of CMS: (1) threshold speed should be set at approximately 4.8 km/h (3 mi/h) greater than the posted speed limit in order to warn drivers, (2) CMS should be placed justbefore the beginning of the actual activity area, and (3) the message should read "You are speeding slow down" or "High speed slow down."

None

The Effect of Crosswalk Markings on Vehicle Speeds in Maryland, Virginia, and Arizona (FHWA-RD-00-101)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Carol Tan Esse

Knoblauch, R.L., and Raymond, P.D.

August 2000

9

http://www.tfhrc.gov/safety/pedbike/index.cfm

Field Test

Normal

Light Vehicles

To determine if the presence of crosswalk markings alter drivers’ speeds.

A before/after evaluation of pedestrian crosswalk markings was performed in Maryland, Virginia, and Arizona.Six sites that had been recently resurfaced were selected. All sites were uncontrolled intersections with a speed limit of 56 km/h (35 mi/h). "Before" data were collected after the centerline and edgeline delineations were installed, but before the crosswalk was installed. "After " data were collected after the crosswalk markings were installed. Speed data were collected under three conditions: (1) no pedestrian present, (2) pedestrian looking, and (3) pedestrian not looking. All pedestrian conditions involved a staged pedestrian.

• Study locations: Maryland, Virginia, and Arizona.
• All sites were uncontrolled intersections with a stop control on the minor leg.
• Under the "before" conditions, all other roadway delineations were installed, but the crosswalk had not yet been installed.
• "After" condition data were collected after the crosswalk markings were installed.
• The speed limit at all sites was 56 km/h (35 mi/h).
• All sites were observed under the following three pedestrian conditions:
  • "No Pedestrian": Speeds were measured with no pedestrian present.
  • "Pedestrian Looking": A staged pedestrian approached the crosswalk, stopped at the edge of the curb as though waiting to cross, and looked square at the oncoming traffic.
  • "Pedestrian Not Looking": A staged pedestrian approached the crosswalk, stopped at the edge of the curb as though waiting to cross, and looked directly ahead.
• Traffic speed was measured by timing vehicles between two marked spots approximately 54.9 m (180 ft) apart.

Pedestrians, Safety, Crosswalks, Crosswalk Markings, Unsignalized Intersections

• Because of the inexplicable large speed reduction found in the No Pedestrian condition at site 5, it was decided to exclude site 5 from the analysis of all sites combined.
• Overall, the crosswalk alone resulted in a speed reduction (average speed reduction of 3.32 km/h) that was significant (see table below).
• In the Pedestrian Looking scenario, there was a small decrease in speed (0.28 km/h) that was not significant.
• In the Pedestrian Not Looking scenario, there was a significant decrease in average speed (2.61 km/h).

• The results indicate a slight reduction at most, but not all, of the sites.
• Overall, there was a significant reduction in speed under both the No Pedestrian and the Pedestrian Not Looking conditions.
• It appears that crosswalk markings alone make drivers on relatively low-speed arterials more cautious and more aware of pedestrians.

None

Evaluation of Work Zone Speed Reduction Measures

Center for Transportation Research
and Education
Iowa State University
2901 South Loop Drive, Suite 3100
Ames, IA 50010-8632

COTR:

Not Specified

Maze, T., Kamyab, A., and Schrock, S.

April 2000

141

None

Literature Review, Survey

Degraded

All

• Study work–zone speed–reduction strategies.
• Explore transportation agencies’ policies regarding managing speeds in long-term, short–term, and moving work zones.

This report consists of three chapters. The first chapter, "Literature Review" examines the current speedreduction practices in work zones and provides a review of the relevant literature. The speed control strategies reviewed in this chapter range from posting regulatory and advisory speed limit signs to using the latest radar technologies to reduce speeds in work zones. The second chapter, " Technology Description," includes a short writeup for each identified speed control technique. The writeup includes a description, the results of any field tests, the benefits, and the costs of the technology or technique. The third chapter, "Survey," provides summaries of the response to each question of a survey administered.

Survey:

• The survey consisted of six multipart questions.
• Every State DOT and a number of non-DOT transportation agencies in some States were contacted.
• Surveys were sent to 63 State transportation agencies. Thirty-nine responses were received.
• Responses were entered into a database to allow queries to be conducted on each individual question.

Speed Reduction, Work Zone

Literature Review:

• Almost every transportation agency posts regulatory and advisory speed signs to inform motorists of the reduced speed limit in work zones. There are also a few agencies that place flaggers. Some agencies have experimented with lane narrowing and other advanced strategies such as using drone radar, speed monitoring displays, removable rumble strips, and optical bars.
• Flagging and police enforcement speed-reduction strategies have had very positive impacts in reducing work-zone speeds. They are, however, labor intensive and can become costly with long-term use.
• Replacing these strategies with innovative technologies, such as robotic flaggers and photo-radar enforcement units, may be practical, more cost-effective solutions.
• None of the techniques described individually is capable of reducing vehicle speeds to the desired level.
• The most effective speed reduction will probably involve some combination of the techniques described inthis literature review.

Technology Description:

• Safety Alert System (Cobra Electronics Corporation): This is a warning system that alerts drivers of emergency vehicles, road hazards, and trains. Research indicates that after the transmitter placement, average passenger car and truck speeds were reduced by 25 and 45 percent, respectively.
• Safety Warning System (SWS) (MPH Industries, Inc.): This system consists of a transmitter and a receiver. The transmitter can be mounted on the outside of a vehicle. The SWS transmitter sends warning messages concerning road hazards to drivers of vehicles equipped with SWS detectors.
• Speed Monitor Display (MPH Industries, Inc.): Speed displays use a radar device to detect and display the speeds of approaching vehicles. Speed monitoring displays are not generally used to enforce speed limits and issue citations; rather, the assumption is that motorists will drive slower once they see their excessivespeed on the display.
• SpeedGuard Speed Monitor Display (Stalker, A Division of Applied Concepts, Inc.): SpeedGuard is a trailer-mounted radar system that displays the speeds of approaching vehicles on a high-intensity, 60.9-cm (24-inch) LED. There are several options when using SpeedGuard. When the unit detects a target vehicle traveling over the speed limit, a strobe lamp flashes toward the offending driver to simulate photo radar. It also alerts workers in work zones of approaching high-speed vehicles.
• Wizard Work Zone Alert and Information Radio (TRAFCON Industries, Inc.): This is designed to give drivers of heavy trucks enough advance warning of delays at upcoming construction sites or incidents. The wizard unit automatically broadcasts an alert message over any Citizen ’s Band (CB) channel.
• Removable Rumble Strips (Advance Traffic Markings, A Division of Patch Rubber Company): Removable rumble strips are designed forplacement at construction sites to alert motorists of upcoming roadwayconditions

Survey:

• During construction activities, most participating State agencies reported reducing speed limits to 16.1 km/h (10 mi/h) below the normal posted speed. There are a few agencies that even consider reducing speed limits by 32.2 km/h (20 mi/h).
• Among the 12 identified speed-reduction strategies, the use of regulatory speed limit signs and police enforcement are the most common practices reported by the agencies. However, only 7 percent of the participating agencies consider the use of regulatory signs to be an effective speed-reduction strategy.
• The survey results indicate that the use of changeable message signs (CMS) by 18 out of 34 agencies might be an indication of their potential in reducing work-zone speeds. A number of these agencies use CMS in conjunction with radar to detect and display the speeds of approaching vehicles.

See Key Results above.

None

Handbook of Speed Management Techniques (FHWA/TX-00/1770-2)

Research and Technology
Transfer Office
Texas Department of Transportation
P.O. Box 5080
Austin, TX 78763-5080

COTR:

Not Specified

Parham, A.H., and Fitzpatrick, K.

September 1998

248

None

Handbook

Normal

Not Specified

To identify speed management techniques that are used throughout the country and develop a handbook documenting these techniques.

This handbook was created to provide practitioners with basic information regarding speed management techniques, including descriptions, photographs, experiences of agencies that have used the techniques, and lessons learned.

The techniques are divided into the following four categories:

• Roadway Design Techniques: Physical measures designed to alter the driver’s path.
• Road Surface Techniques: These change the surface of the roadway by adding vertical elements such as speed humps, by narrowing the roadway, or by drawing the driver’s attention through the use of pavement markings.
• Traffic Control Techniques: For example, signs and beacons that are used to alert drivers of allowable speeds or to warn them of an approaching hazard or other traffic control device, such as a traffic signal.
• Enforcement Techniques: These techniques remind drivers of speed limits and of the speed they are traveling through speed displays or additional enforcement.

Speed Management, Traffic Calming, Devices

The key advantages and disadvantages are described above for each technique. Enforcement techniques are also discussed in the report.

None

Synthesis of Safety Research Related to Speed and Speed Management (FHWA-RD-98-154)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Not Specified

Stuster, J., Coffman, Z., and Warren, D.

July 1998

24

http://www.tfhrc.gov/safety/speed/speed.htm

Literature Review

Normal

Not Specified

To present a synthesis of research findings on the safety effects of speed, speed limits, enforcement, and engineering measures to manage speed.

This document provides a review of safety research related to speed and speed management. This review builds upon a similar synthesis prepared in 1982. This synthesis highlights the relationships among vehicle speed and safety; factors influencing speeds; and the effects on speed and crashes of speed limits, speed enforcement, traffic calming, and other engineering measures intended to manage speed.

• A systematic review of the literature concerning safety research related to speed and speed management was conducted. Initial listings of citations were generated by using key word filters on several bibliographic databases.
• The most productive databases were those of the National Technical Information Service (NTIS), the Knight-Ridder Transportation Resources Index, and the Transportation Research Information Service (TRIS).

Speed, Speed Management, Safety, Speed Limits, Traffic Calming

Speed-Safety Relationships:

• Solomon (1964) found a relationship between vehicle speed and crash incidence that is illustrated by a U-shaped curve. Crash rates were lowest for travel speeds near the mean speed of traffic and increased with greater deviations above and below the mean.

Factors Influencing Speed:

• Speed choice can be influenced by driver age; gender; attitude; perceived risks of law enforcement; weather, road, or vehicle characteristics; speed zoning; speed adaptation; impairment; or simply "running late."

Enforcement:

• The following areas of speed enforcement were discussed: Mobile and stationary patrol vehicles, aerial enforcement, radar and laser speed monitoring, automated enforcement, drone radar, speed feedback indicators, Public Information and Education (PI&E), and traffic enforcement notification signs.

Engineering Measures:

• The current review found the mosteffective traffic-calming measures to involve vertical shifts in the roadway, such as speed humpsand speed tables. However, the effectiveness of these is dependent upon spacing.
• Greater reductions in vehicle speeds and crashes are achieved when combinations of measures are used and when traffic calming is implemented systematically over a wider area than a single neighborhood.
• Reductions in the incidence and severity of crashes of 50 percent or more are frequently reported (see table). However, most trafficcalming projects result in reductions in traffic volume and many of the safety studies do not take this diversion into account.

• There is evidence that crash risk is lowest near the average speed of traffic and increases for vehicles traveling much faster or slower than average.
• Despite the large number of references concerning traffic calming, very few reports include the results of a systematic evaluation. In many cases, traffic volume and speed are reduced. As a result of the traffic diversion, crashes may be migrating to other roads.
• More research is needed to assess the systemwide impacts and permit comparisons to be made among individual and combinations of traffic-calming measures.

None

Passive Pedestrian Detection at Unsignalized Crossings

(Transportation Research Record, 1636, pp. 96-103)

DKS Associates
921 S.W. Washington Street, Suite 612
Portland, OR 97205-3500

COTR:

Not Specified

Beckwith, D.M., and Hunter-Zaworski, K.M.

1997

26

None

Field Test

Normal

Not Specified

To evaluate the use of passive pedestrian detection sensors at unsignalized crossings.

This report includes a discussion of a project conducted by the City of Portland, OR, to evaluate available sensor technologies for passive pedestrian detection, design of a crossing to utilize these sensor technologies, and a preliminary evaluation of how well the sensors operate once installed at the crossing.

Existing Technologies Research:

• Literature was reviewed and telephone interviews with sensor manufactures were conducted.

Preliminary (Short-Term) Testing:

• The objective was to test the initial group of sensors identified as possible candidates to determine if the detectors could detect pedestrians, what types of detection zones could be expected, location requirements, and if there were an excessive number of false calls.
• A location that showed a high level of pedestrian traffic adjacent to a bus stop was chosen to conduct the preliminary testing of each sensor.
• Each sensor was mounted on a pedestrian signal and positioned to detect pedestrian traffic. The sensors were then connected to a type 170 controller at the location. The controller cabinet was retrofitted with two lights mounted on top that lit up each time a pedestrian entered the detection zone of the sensor.
• Each intersection chosen was equipped with video cameras and a video cassette recorder that allowed formonitoring of the sensors over extended periods without having an observer present at all times.

Secondary (Long-Term) Testing:

• Based on the preliminary testing, the infrared sensor was chosen for monitoring the landing areas of the crossing and the Doppler radar was chosen for monitoring the area within the crossing itself.
• The sensors actuate yellow beacons placed above reflective yellow pedestrian crossing signs suspended above the crossing. A four-sensor crossing was used that consisted of two passive infrared (1 and 4) and two Doppler radar (2 and 3) sensors.

Pedestrian Crossing, Sensor Technologies, Passive Pedestrian Detection

Summary of Existing Technologies:

• Literature on passive pedestrian detection consists of limited articles on the following techniques: PUFFIN (Pedestrian User Friendly Intelligent Signals) and PUSSYCAT (Pedestrian Urban Safety System and Comfort at Traffic Signals). These crossings use a combination of devices such as piezometric pads and Doppler radar or passive infrared sensors in detecting the presence of pedestrians in Great Britain and the Netherlands.
• Five types of technologies that have been used in detection systems and could possibly be used for passive pedestrian detection: Passive infrared (PIR), ultrasonic, Doppler radar, video imaging, and pieozometric.
  • Of the potential technologies reviewed, the following technologies were selected for the project: Passive infrared, microwave radar, and two ultrasonic sensors.

Preliminary Test Results:

• Of the detectors chosen, three were tested. Theseincluded passive infrared, Doppler radar, and one ultrasonic sensor.
• The infrared sensor had a very good detection rate and was versatile regarding sensor position. This allows the detector to be installed in many different types of applications with minimum upgrading required to existing facilities and also low installation time and cost.
• The Doppler radar sensor was the only sensor that effectively detected pedestrians at a distance of 9.1 m (30 ft) or greater and had no maximum operating angles. It also had a detection zone that was wide enough to cover the width of a standard crossing. Therefore, only one or two sensors is needed to effectively monitor a crossing,keeping installation time and cost at a minimum.

Secondary Test Results:

• Five items were recorded from the location: (1) weather conditions; (2) date; (3) time of day; (4) detection reliability (each item was observed to see whether it false detected (F) with no pedestrian present, detected a pedestrian with no problems (D), intermittently detected a pedestrian (I), or lost detection of a pedestrian (L)); and system shutdown time.
• Of the 60 crossings observed, there were eight intermittent (I) detections with pedestrians present in the Doppler radar zones and one in the passive infrared zones. At no time during any of the observed crossings were pedetrians not detected or caught within the crossing when the system shut down.
• On the average, beacons would remain activated after the pedestrian left the crossing for 32 s. The maximum time recorded for beacons remaining on was 125 s, with a minimum time of 6 s.
• During heavy rainfall, if the passive pedestrian detection system had been activated by a pedestrian, the Doppler radar sensors would remain active, keeping beacons illuminated.

• Through continued research, it is anticipated that the safety of unsignalized pedestrian crossings can be facilitated by using passive pedestrian detection systems.
• The infrared and Doppler radar sensors that passed the preliminary testing discussed in this report have shown encouraging initial secondary test results.

None

Pedestrian Safety in Australia (FHWA-RD-99-093)

Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Carol Tan Esse

Cairney, P.

December 1999

40

http://www.tfhrc.gov/safety/intersect.htm

Literature Review

Normal

Not Specified

This report was one in a series of pedestrian safety synthesis reports prepared for FHWA to document pedestrian safety in other countries.

This report provides a summary of pedestrian crash experience; an overview of crash countermeasures and safety programs; and information on various topics related to pedestrian safety, including pedestrian facilities, traffic-calming measures, innovative devices, education considerations, and enforcement and regulation.

There are three basic source documents used for information on signs and markings for pedestrian facilities, provision and design of pedestrian facilities, and proposed legislative changes. The following is a list of the three source documents:

• The Australian Standard Manual on Uniform Traffic Control Devices.
• Austroads Guide to Traffic Engineering Practice.
• Australian Road Rules (draft).

Australia, Pedestrian Crossings, Local Area Traffic Management, Pedestrian Safety, Pedestrian Signals

Sidewalks:

• A general minimum width of 1.2 m (4 ft) is specified for sidewalks. Wider paths are called for if pedestrian volumes are large, or if provision is required to be made for wheelchairs, or if the facility is to be shared with cyclists.

Midblock Crossings:

• Pelican crossings: These crossings are similar to midblock pedestrian signals, except that during the pedestrian clearance phase, the display facing the motorists changes to a flashing yellow, indicating that vehicles may proceed across the crossing; however, they are required to give way to pedestrians.
• PUFFIN crossings: These crossings use infrared sensors to detect the presence of pedestrians and monitor their progress across the crossing. Trials have recently been held.

Provision for the Disabled Pedestrian:

• Specific ways to provide for disabled people are listed in the Austroads Guide to Traffic Engineering Practice, Part 13, and include: Width of footpaths to accommodate wheelchairs, need for obstruction-free paths, placement of gratings and manhole covers, treatment of ramps and curb ramps, installation of textured paving at waiting areas to provide tactile cues for the visually impaired, loops to detect wheelchairs and allow longer pedestrian green times at signalized crossings, provision of information on routes used by the visually impaired, and signage of facilities and routes for the disabled.

School Zone Safety:

• School zone safety is generally addressed by the provision of warning signs to indicate a school zone, and the provision of pedestrian-operated traffic signals or children’s crossings, depending on pedestrian and vehicle flows. They may be enhanced by the provision of curb extensions (bulbouts).

Traffic Calming for Pedestrians:

• Local Area Traffic Management (LATM): LATM has been widely adopted in Australia over the last20 years. LATM aims to effect changes by altering the physical environment rather than by regulations and their enforcement.
• Effects of humps and raised platforms: The results from a study where pedestrian ramps were installed along a busy shopping street showed that unjust crashes fell from 18 per year to 3 per year, pedestrian delay was reduced, and traffic flow and speed were also reduced. Curb extensions appear to have been relatively successful. Curb extensions on their own produced an adjusted reduction of 27 percent, and curb extensions at existing pedestrian crossings produced an adjusted rate showing a 44 percent reduction.
• Roundabouts: The splitter islands on the approaches to the roundabout give pedestrians the opportunity to make staged crossings as does a median or pedestrian refuge. Although roundabouts are recognized as a treatment that is effective in reducing the severity of crashes, there does not appear to be Australian data on their effect on pedestrian crashes.

Innovative Devices:

• Infrared sensors: Research indicated that a 40 percent reduction in vehicle delays was found with infrared sensors. In addition, there was no increase in red-light running or other driver behaviors that might adversely affect safety. There was an increase in pedestrian compliance with signals. There was a significant reduction in the percentage of pedestrians starting to cross before the green (10 percent).

• PUFFIN crossings with infrared detectors seem promising.
• Pelican crossings are likely to find ready application, and having them set up for double-cycle operations appear to offer benefits.
• Australia was particularly innovative in developing the "Safe Routes to School" program, which integrates education, route selection, and engineering treatments to increase pupil safety.
• Also in development is the "Walk With Care" program designed for the elderly.

None

A Review of Pedestrian Safety Research in the United States and Abroad (FHWA-RD-03-042)

Office of Safety Research
and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Carol Tan Esse and Ann Do

Campbell, B.J., Zegeer, C.V., Huang, H.H., and Cynecki, M.J.

January 2004

150

https://www.fhwa.dot.gov/environment/bikeped/pedbiketrb2005.htm

Literature Review

Normal

All

To provide an overview of research studies on pedestrian safety, including the details of pedestrian crash characteristics, measures of pedestrian exposure and hazard, and specific roadway improvements and their effects on pedestrian safety.

This report is an update resulting from two earlier reports. The most recent was Synthesis of Safety Research: Pedestrians , by C.V. Zegeer (FHWA-SA-91-034). The earlier work was chapter 16, "Pedestrian Ways," by R.C. Pfefer, A. Sorton, J. Fegan, and M.J. Rosenbaum, which was published by FHWA in Synthesis of Safety Research Related to Traffic Control and Roadway Elements. This updated report includes results from numerous studies, both foreign and domestic.

• Readers will find the details of pedestrian crash characteristics, measures of pedestrian exposure and hazards, and specific roadway features and their effects on pedestrian safety.
• Such features include crosswalks and alternative crossing treatments, signalization, signage, pedestrian refuge islands, provisions for pedestrians with disabilities, bus stop location, school crossing measures, reflectorization and conspicuity, grade-separated crossings, traffic-calming measures, and sidewalks and paths.
• Pedestrian educational and enforcement programs are also discussed.

Pedestrians, Safety Research, Crashes, Countermeasures, Education, Enforcement

• Fatal pedestrian crashes tend to occur during nighttime hours.
• Pedestrian crashes are more frequent on Friday and Saturday and less frequent on Sunday.
• The largest percentage of pedestrian fatalities falls into the 25-to-44 age category.
• Alcohol is an important factor in pedestrian crashes. A North Carolina study showed that between 42 and 61 percent of fatally injured pedestrians had blood alcohol concentration (BAC) levels of 0.10 or greater.
• Overall, 74 percent of pedestrian crashes occur where there is no traffic control, 7 percent where there is a stop sign, and 17 percent in the presence of a traffic signal.
• Most pedestrian crashes occur where speed limits are low or moderate.
• Although most pedestrian crashes occur in urban areas, 60 percent of all crashes in urban areas do not occur at intersections. This compares to 75 percent of child pedestrian crashes that occur not at an intersection (see figure).

Figure A. Pedestrian crashes (fatal and nonfatal) by age and intersection vs. nonintersection (Source: General Estimates System, NHTSA, 1990).

• More substantial improvements are recommended to provide for safer pedestrian crossings, such as adding traffic signals (with pedestrian signals) when warranted, providing raised medians, installing speedreduction measures, and/or others.
• Providing raised medians on multilane roads can substantially reduce pedestrian crash risk.
• There is evidence that substantially improved nighttime lighting can enhance pedestrian safety.
• Allowing vehicles to make a right turn on red (RTOR) maneuver appears to result in a small, but clear, safety problem for pedestrians. Countermeasures that have been effective in reducing pedestrian risks related to RTOR include illuminated No Turn on Red (NTOR) signs, offset stop bars, variations in NTOR signs, and others.
• Curb medians provide a safer environment for pedestrians compared with two-way, left-turn lanes (TWLTLs), while undivided highways have the highest crash risk for pedestrians in TWLTL settings.
• Numerous treatments exist to address the needs of pedestrians with disabilities, such as textured pavements, audible and vibrating pedestrian signals, larger signs and pedestrian signals, wheelchair ramps, and others.
• Careful placement of bus stops can affect pedestrian safety. Use of bus stops on the far side of an intersection and at locations with good sight distance and alignment is important.
• Overpasses and underpasses can substantially improve safety for pedestrians who need to cross freeways or busy arterial streets. However, such facilities must be carefully planned and designed to encourage pedestrians to use the facilities and not continue to cross at street level.
• Traffic-calming measures such as street closures, speed humps, chicanes, traffic curbs, diverters, and others are in use in various U.S. cities. Many of these measures have been found to effectively improve safety forpedestrians and/or traffic as a whole.

None

Intelligent Traffic Signals for Pedestrians: Evaluation of Trials in Three Counties

(Transportation Research Record Part C, 6, pp. 213-220)

Institute for Transport Studies
University of Leeds
Leeds LS2 9JT, UK

COTR:

Not Specified

Carsten, O.M.J., Sherborne, D.J., and Rothengatter, J.A.

1998

17

None

Field Test

Normal

Not Specified

To evaluate the effects of the Vulnerable Road User Traffic Observation and Optimization (VRU-TOO) traffic.signal on pedestrian behavior and safety.

The DRIVE II project VRU-TOO carried out trials of innovative pedestrian signalized crossings that were designed to be more responsive to pedestrians’ needs and thereby improve pedestrian safety and comfort. These advanced crossings were installed at sites in three European countries and a comprehensive evaluation of the impacts was carried out, with a particular emphasis on changes in pedestrian behavior and safety.

• The generic VRU-TOO system: Microwave detectors were mounted on traffic signals to register the approach of pedestrians.

Location Sites Studied:

• Leeds, England: Three crossings along one quadrant of the new one-way loop road that encircles the city center were fitted with the VRU-TOO system.
• Porto, Portugal: The crossing was on a major east-west arterial, linking the city center with the coastal industrial zone.
• Elefsina, Greece: The location was a crossroad in the town center on what had been the main Athens-to-Corinth highway, prior to the building of a bypass.

Evaluation:

• For all locations except Elefsina, a comprehensive evaluation was carried out covering pedestrian safety, comfort and behavior, and the side effects on vehicle traffic.
• In Elefsina, a full evaluation was only carried out for the western crossing (because of the availability of equipmentand possible video locations).
• The main criterion evaluated was pedestrian/vehicle conflicts, which were counted by observers.
• Other criteria evaluated included the following: Percentage of pedestrians arriving on red who violated the red light, especially the percentage violating red when vehicle traffic had a green, and the number of encounters between pedestrians and vehicles.

Pedestrians, Pedestrian Safety, Pedestrian Crossings, Intelligent Transport System

Safety:

• When the three sites in Leeds are combined, the total number of conflicts observed was 55 before implementation and 45 after implementation. This change is significant at the 0.10 level, but not at the 0.05 level (p = 0.08, one-tailed).
• In Porto, the number of conflicts in the "before" study was 133, and the number in the "after" study was 130, so the overall number of conflicts did not change significantly.
• The overall number of conflicts in Elefsina changed significantly between the before and after periods from 82 to 64 (significant at the p < 0.05 level, one-tailed).

Comfort:

• In Leeds, the expected delay was reduced at all three sites, with a particularly large reduction at site 3.
• In Porto, the expected delay did not change at crossing 1, whereas at crossing 2, it was considerably reduced from a mean of 37 s before to one of 29 s after.

Effects on Vehicle Traffic:

• There was no significant change in vehicle flow through the relevant sector of the one-way city center loopin Leeds between the before and after periods. Average journey time increased from 2.6 minutes (min) in the "before" survey to 3.8 min in the "after" survey, indicating some negative effects on vehicle movement.
• In Porto, total hourly vehicle flow through the junction decreased by 13 percent between the before and after observations. Mean journey time increased by 4 percent eastbound along the main road, by 3 percent westbound along the main road, and by 15 percent along the side streets. In no case was the increase in journey time statistically significant. There were no significant changes in queue lengths.
• In Elefsina, queue lengths were observed. In the westbound direction, the mean number of cars queuing decreased from 6.7 in the before period to 5.9 in the after period. The number of cycles in which no passenger car was observed to queue increased from 23 to 40. In the opposite direction, the mean number of cars queuing decreased from 3.7 to 3.3, and the number of cycles in which no passenger car waited increased from 26 to 65.

• While there were important differences in the impacts at the various sites, partly reflecting differences in system implementation, there were general gains in safety and comfort for pedestrians.
• These improvements were obtained without major side effects on vehicle travel.
• Further experimentation with signal timings in order to obtain additional benefits in terms of pedestrian safety and comfort, as well as the development of more extensive applications covering urban corridors or areas, is encouraged.

None

Bicycle Safety-Related Research Synthesis(FHWA-RD-94-062)

Office of Safety and Traffic Operations
Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

COTR:

Carol H. Tan

Clarke, A., and Tracy, L.

April 1995

152

None

Literature Review

Normal

All

• Summarize bicycle safety-related research and applied research since 1981 in the United States.
• The report has been developed for the benefit of researchers and practitioners in the field.

This report reviews research into current levels of bicycle use, potential levels of use, and the benefits bicycling can bring to society; identifies the scale and nature of crashes related to bicycle use; discusses engineering countermeasures that have been tested to prevent crashes; brings readers up to date with current practices related to bicycle facility selection and design; highlights surface irregularities that endanger bicyclists, as well as countermeasures to correct them; introduces readers to traffic-calming techniques; reviews bicyclists ’ equipment safety and helmet use; and reviews educational programs and enforcement programs to improve safety.

As part of the development of this report, case studies were commissioned from the Netherlands, Great Britain, Australia, Japan, Germany, and Denmark to add international experience and perspective.

Bicycle, Bicycle Safety, Bicycle Facilities, Bicycle Helmets, Bicycle Use, Highway Design, Traffic Calming

Section 1. Bicycling in the United States in the 1990s:

• This section discusses increasing bicycle sales and use, the potential for bicycling in the United States, factors influencing bicycle mode choice, costs and benefits associated with bicycling, and international comparisons.

Section 2. Bicycle Crash Experience:

• This section describes bicycle crashes in general, bicycle/motor vehicle crashes, crash causes, bicyclist behavior, motorist behavior, alcohol involvement, bicyclist statistics, economic impacts of bicycle/motor vehicle crashes, nonmotor-vehicle-related bicycle crashes, and bicycling injuries.

Section 3. Intersection Countermeasures:

• Stop signs: Where the potential exists to develop trails and bicycle boulevards, the number of stop signs can be diminished. Where this cannot be done, education and consistent enforcement of bicyclist violations are likely to be the best solution to reducing bicycle/motor vehicle crashes at intersections controlled by stop signs.
• Traffic signals:Bicycle-sensitive traffic signal detectors are available and are being used quite extensively in California and other States. There are appropriate and effective methods of guiding bicyclists to the most sensitive part of older loop detectors to aid in their detection. An appropriate formula for determining signal timing has been developed.
• Right turn on red (RTOR): RTOR laws have had a negative impact on the safety of bicyclists. At intersections with high crash records and/or significant levels of bicycle use, RTOR prohibitions should be considered.
• Advanced stop lines:Advanced stop lines and other innovative intersection designs and road markings have not been used in the United States despite their growing use in other countries. They should be tested at various locations to determine their applicability.
• Roundabouts: Bicycle safety is not well served by the use of large roundabouts designed to increase vehicle speed or capacity through intersections. Traffic circles, however, show great potential for calming traffic in residential areas and in reducing the speed of vehicles.