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Federal Highway Administration > Publications > Public Roads > Vol. 66 · No. 4 > Reducing Points of Conflict

January/February 2003
Vol. 66 · No. 4

Reducing Points of Conflict

by Joe G. Bared, Patrick Hasson, Fred N. Ranck, Hari Kalla, Robert A. Ferlis, and Michael S. Griffith

FHWA targets intersection safety.

An intersection is, at its core, a planned point of conflict in the highway system. Crashes related to these points of conflict in the United States resulted in almost 9,000 fatalities and about 1.5 million injuries in 2001 alone. These incidents represented 44 percent of all reported crashes in the Nation, or a staggering 2.8 million.

Intersection crash involving an SUV and a concrete delivery truck. Patrick Hasson FHWA

Violent intersection crashes such as this one between an SUV and a concrete delivery truck are all too common and exact a high toll.

Clearly, intersection safety is a critical component of overall highway safety. Moreover, because of the nature of the safety problem at intersections, solutions often require committed and coordinated action on the part of a variety of traditional and nontraditional partners.

Transportation and safety organizations throughout the country, as well as enforcement agencies, traffic engineers, and public education and outreach groups—either government officials or local citizen groups—must work together to make a substantive difference in the reduction of intersection-related crashes. And they are.

The Federal Highway Administration (FHWA) identified safety as one of its Vital Few goals. As a means of focusing its safety efforts, FHWA's strategic goal is to reduce the number of highway-related fatalities and injuries by 20 percent by 2008. Additionally, FHWA also established the objective of reducing intersection fatalities 10 percent by 2007. To this end, FHWA and a number of other highway organizations are orchestrating a variety of innovative activities and research initiatives. From informational guidebooks to research programs and international scans, FHWA and its partners are working to improve intersection safety through the design of smarter roundabouts and signalized intersections, reduced red light running, and other cutting-edge research to increase the safety of America's road users.

New Tool for Roundabouts

Research indicates that well-designed roundabouts with single-lane and double-lane entries, where conditions are appropriate, can be safer and more efficient than conventional intersections. Indeed, injury and fatal crashes can be reduced 20 percent for traffic flows of double-lane roundabouts with approximately 40,000 average daily traffic (ADT), and by as much as 70 percent for traffic flows of single-lane roundabouts up to 20,000 ADT. Roundabouts also mean less delay to motorists as opposed to conventional stop- or signal-controlled intersections.

A key intersection treatment tool by FHWA's Intersections Research program is its report, Roundabouts: An Informational Guide (2000). The guide provides comprehensive educational and prescriptive information, covering all aspects related to roundabouts: from policy considerations to planning, traffic analysis, geometric design, traffic control devices, and special applications. The guide is widely used as a primary reference and authority on the subject.

Speed and Path Choice for Roundabouts

FHWA's Human Centered Systems (HCS) Team in Safety Research and Development is examining the influence of geometry and lane delineation on motorists' choice of speed and path in double-lane roundabouts. By conducting field studies on two Maryland double-lane roundabouts, the research team aims to provide additional information on the speed imposed on motorists by geometric design. The results will be used to update the geometric design of roundabouts. The update will augment bicyclist and pedestrian safety at roundabouts, including individuals with disabilities.

In the Maryland study, vehicles are being observed through cameras mounted high above the intersections, to assess lane position and speed for individual vehicles before they enter the roundabout, once they are in it, and when they exit. In addition to the field tests, HCS researchers in the laboratory are examining path and speed choices of drivers. With simulated roundabouts, researchers can examine the effects of two alternative roundabout entry geometries and markings, without the need to build or modify a roundabout. To validate the simulation method, the roundabouts observed in the field were replicated in the simulator.

The results of both field and simulated research will be available in the spring of 2003.

Intersections with numerous driveways in close proximity. Patrick Hasson FHWA

Intersections like this one that have numerous driveways in close proximity offer unique challenges to engineers and special risks to users.

Improving Roundabout Safety, Design, and Operation

Although modern roundabout design is relatively new to the United States, perceived differences in motorists' behavior raise questions about how appropriate some international research and practices are for adoption in this country. Additional information on the safety and operation of roundabouts in the United States is needed to help planners and designers determine where roundabouts would reduce intersection crashes and congestion, and how current design criteria could be improved.

To this end, FHWA is contributing to the Transportation Research Board's (TRB) National Cooperative Highway Research Program's (NCHRP) Project 3-65, Applying Roundabouts in the United States. This project will develop methods of estimating the safety and operational impacts of U.S. roundabouts and, ultimately, refine roundabout design criteria. The NCHRP expects that the project will be completed in the summer of 2005. For more information, please visit www4.nas.edu/trb/crp.nsf/NCHRP+projects (click on Area 3).

A roundabout. Phil Demosthenes, Colorado DOT

A roundabout in Golden, CO.

Red Light-Running Guide

One of the primary causes of crashes at signalized intersections occurs when motorists enter intersections when the red signal is displayed and collide with other motorists, pedestrians, or bicyclists who are legally within the intersection. According to the journal Accident Analysis and Prevention, these red light-running crashes, which occur approximately 200,000 times each year, have an alarmingly high injury rate of 45 percent—significantly higher than the injury rate for other crash types, which is 30 percent.

Red light running is a complex problem with no simple cause or solution. Although driver error, such as distractions, inattention, and willful disregard, as well as driver psychology and sociology, play a role in explaining some violations, numerous reports and anecdotal evidence suggest that engineering deficiencies also may be at fault. For example, yellow change intervals can be set so low that they "trap" motorists into running red lights. Similarly, intersections with limited sight distance to the signals make it difficult for a motorist to see the red signals in time to avoid running the red light.

To provide better guidance on the engineering features that contribute to red light running, FHWA and the Institute of Transportation Engineers (ITE) are working on a new guide, Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red Light-Running Crashes. Intended for engineers, law enforcement, and other officials, the guide provides a comprehensive background on the characteristics of the red light-running problem, presents engineering measures that can be implemented to solve it, and helps users select appropriate engineering measures to meet the specific needs and conditions. The guide will be publicly available in January 2003.

Tractor-trailers going through intersection with a red light. Precisioin Traffic Safety Systems Corporation

When motorists disobey traffic control devices, as the tractor-trailer drivers in this photo are doing they put themselves and others in great danger.

Improving Collision Prediction

Being able to predict potential driver behavior or traffic collisions successfully is critical to improving safety on the road. But making these predictions is easier said than done. Existing crash models are contingent upon retrospective crash statistics, which may not provide a large enough sample. Additionally, transportation engineers may not have the right information to represent correctly specific conditions on a road or at an intersection. Relying solely on crash statistics for crash modeling can be costly in terms of both human safety and infrastructure investment.

To enable safety engineers and roadway designers to work around these limitations and better evaluate the safety and mobility of roadway and intersection designs and treatments, FHWA is in the process of developing safety measures from traffic simulation models that can be complementary to actual crash data.

Specifically, FHWA researchers are identifying and defining appropriate and measurable surrogate actions or events, and then evaluating the applicability and capabilities of existing traffic simulation models. Useful measures sought by FHWA include information on the expected time for two vehicles to collide if they remain at their present speeds and paths, and the time lapse between cars and the amount of space necessary for changing lanes. Once surrogate measures are defined, functional requirements and logic for simulation software that depicts safety measures for intersections will be developed.

FHWA expects to complete the initial phase of the project by early 2003. The initial phase involves exploring surrogate safety measures within simulation models, evaluating the capabilities of traffic simulation models, identifying functional requirements, and developing a logic/algorithm for a surrogate safety assessment methodology. Planning is now underway for the second phase, which will include the promotion of a surrogate safety assessment module, as well as validation and incorporation of the safety measures into existing simulation software.

Signalized Intersections

FHWA is in the process of designing an informational guide for medium- and high-volume signalized intersections. The goal is to synthesize safety and operational characteristics by developing comprehensive guidelines for all design and operational features for all highway users. FHWA also intends to develop a research program for conventional and innovative intersections, median U-turns, and displaced left-turn lanes.

The guidelines, expected to be complete by the end of 2003, will address all considerations related to signalized intersections comprehensively, taking the reader step-by-step through the project development process, legal considerations, user considerations, symptoms identification, causal evaluation, treatments, implementation, and monitoring.

International Scan on Signalized Intersection Safety

To identify innovative safety practices in the planning, design, operation, and maintenance of signalized intersections, in May 2002, FHWA and the American Association of State Highway and Transportation Officials (AASHTO) sponsored a European scan to Germany, the Netherlands, Sweden, and the United Kingdom. The team included 13 representatives, with members from FHWA, AASHTO, ITE, TRB, State departments of transportation (DOTs), municipal transportation agencies, universities, and the private sector. Members possessed diverse technical skills and expertise in the planning, design, operation, and maintenance of signalized intersections.

Coordinated by FHWA's Office of International Programs, the scan was designed to identify and evaluate promising and readily executable solutions and programs for intersection safety that could be implemented in the United States. Specifically, the scan targeted six major areas of interest. The first was the selection, design, installation, operation, and maintenance of traffic control devices at signalized intersections, with a focus on the safety implications at each stage. Second and third were innovative traffic control devices and geometric designs for signalized intersections. The fourth focus was procedures for problem identification, evaluation, and countermeasure selection at signalized intersections with safety problems; fifth, low-cost safety improvements for signalized intersections; and the final focus was research projects focused on safety issues at signalized intersections.

A signalized intersection at Tysons Corner, VA. Joe Bared FHWA

A signalized intersection at Tysons Corner, VA.

The team met with national and municipal transportation administrations and ministries, university faculties, research organizations, and industry representatives in the four countries. They observed specific safety improvements in the field and gathered information on site-specific studies and examples of safety improvements. Through discussions and site visits, the participants also identified potential barriers or special needs regarding implementation of such strategies and programs in the United States.

Key Findings

Based on the knowledge gained, the team developed a set of observations, key findings, recommendations, and ideas for implementation. The European countries share a number of common characteristics with respect to intersection safety:

  • One national agency is responsible for developing and maintaining a national highway system.
  • Each national organization provides safety guidance with different target levels of crash reduction focused on fatalities and serious injuries.
  • Typically, specific intersection safety issues are identified, studied, and corrected at the local level with support from national and State agencies.
  • Strong emphasis is placed on protecting the vulnerable road user (pedestrians and bicycles).
  • Safety concerns generally outweigh congestion and mobility issues.
  • Shorter cycle lengths at signalized intersections are used to improve pedestrian and bicycle operations.
  • Automated photo enforcement is used to minimize unsafe driver behavior at intersections (speeding and red light running).
  • Vehicle detectors and signal controller software packages are used to vary signal timings and address congestion and "dilemma zone" issues. (The dilemma zone is the area where drivers find themselves if, when they see the yellow indication, they lack adequate distance to stop before the intersection but are too far away to enter the intersection before the red indication.)

Area view of complex intersection in the Netherlands. Fred Ranck, FHWA

Highway engineers struggle with a complex array of signals, markings, and signs to make intersections, like this one in the Netherlands, as simple for users to navigate as possible.

According to Office of Safety Chief Highway Safety Engineer Rudy Umbs, the team's preliminary recommendations include: (1) developing a model photo enforcement process/program for implementation at signalized intersections, (2) identifying and implementing demonstration projects for enhanced dilemma zone detection, and (3) developing a pilot project to control speed through intersections using a combination of practices implemented in Europe. Formal recommendations will be included in the final scan report scheduled for completion in spring 2003. The team's final implementation strategy will be reflected in the Scan Technology Implementation Plan (STIP).

Crowded intersection in London. Fred Ranck, FHWA

Cities in the United States and around the world must meet the demand for movements of large numbers of people and vehicles through the same space. This crowded intersection is a street in London.

Safety Effectiveness of Intersection Left- and Right-Turn Lanes

Does adding a turn lane make intersections safer? The answer is a resounding yes. But how much safer?

Well-defined right-turn lane in Sherman County, OR. Midwest Research Institute

Well-defined right-turn lanes, such as this one in Sherman County, OR, improve the safety of motorists entering intersections.

A new FHWA TechBrief, "Safety Effectiveness of Intersection Left- and Right-Turn Lanes," presents the results of research on the safety effectiveness of providing left- and right-turn lanes for at-grade intersections.

Researchers selected three types of sites for the study from eight of the participating States: improved or treatment sites, comparison sites, and reference sites. The improved or treatment sites are intersections at which a left- or right-turn lane was added and for which data on intersection geometrics, traffic volumes, and traffic accidents were available for time frames before and after the improvement. For 260 of the 280 improved intersections, the researchers selected a matching comparison site that was not improved during the study period. In addition, they selected 40 reference sites, which were both unimproved and not matched to any particular improved site.

The researchers collected traffic volume data for both the major- and minor-road legs and evaluated traffic accident records for all accidents within 75 meters (246 feet) of each intersection that were related to the presence of the intersection, as designated by the investigating officer or accident coder.

In addition, results are presented in the report for installing left-turn lanes on the major-road approaches to rural intersections and installing right-turn lanes on the major-road approaches to rural and urban intersections. In addition, economic evaluations of the installation of left-turn lanes at various types of intersections were conducted, thereby allowing the calculation of benefit-cost ratios and cost-effectiveness thresholds.

The full research report is available at www.fhwa.dot.gov/research/tfhrc/programs/safety/.

Michael S. Griffith

Expected Percentage Reduction in Total Accidents for Installation of Left-Turn Lanes on Major-Road Approaches to Urban Intersections
Intersection Type
Intersection Traffic Control
Number of Major-Road Approaches

Where Left-Turn Lanes Are Installed

 
 
One Approach % Reduction
Both Approaches % Reduction
Three-Leg Intersection
Stop sign

Traffic signal

33

7

 
Four-Leg Intersection
Stop sign

Traffic signal

27

10

47

19

Source: One of several tables in FHWA's TechBrief FHWA-RD-02-103.

Guidelines for Intersection Partnerships

In cooperation with NCHRP's Project 17-18, FHWA is supporting AASHTO's Strategic Highway Safety Plan. The focus of the plan is to develop and validate guidance documents, and to assist State and local agencies with reducing fatalities in targeted areas, including signalized and unsignalized intersections.

Under this initiative, The Implementation Guidelines to Address Unsignalized Intersections has been developed and validated by selected State and local transportation agencies. The strategies addressed in this guidebook include improving management of access near unsignalized intersections; improving driver awareness of intersections as viewed from the intersection approach; choosing appropriate intersection traffic control to minimize crash frequency and severity; improving driver compliance with traffic laws and control devices at intersections; and reducing operating speeds at intersection approaches. This guidance document will be available in early 2003 in hard copy from TRB and electronically via http://www.transportation1.org/SafetyPlan/ and www.transportation.org.

To address signalized intersections, a draft compendium of strategies for safety at signalized intersections was recently peer-reviewed and is now being revised. Specific means for achieving geometric, operational, and traffic control improvements are among the major strategies recommended for reducing the frequency and severity of intersection conflicts. Major strategies identified include improving sight distance, driver awareness of intersections and signal control, driver compliance with traffic control devices, and access management near signalized intersections. NCHRP expects that the revised compendium will be available by the end of 2003.

A non-signalized T-intersection in rural Virginia. Joe G. Bared, FHWA

A non-signalized T-intersection in rural Virginia.

Safer Intersections Ahead

The federally designated pooled fund Infrastructure Consortium, made up of several State departments of transportation, is working to develop and deploy advanced highway safety technologies. The consortium's initial focus is to develop infrastructure-based intersection collision avoidance systems. Possible technologies include relatively complex systems that could identify safety threats with traffic and pedestrian/bicycle sensors, analyze traffic movements to determine appropriate means to avoid the threat, and communicate the needed responses to drivers. This communication could be infrastructure-only, such as the activation of a strobe light when a driver is about to violate a stop sign, or it could be vehicle-highway cooperative, such as messages inside vehicles that warn drivers who are about to violate a traffic signal or alert them to potential collisions with traffic signal violators. The Infrastructure Consortium members are hopeful that infrastructure-based intersection collision avoidance systems could be deployed as early as 2010. In addition to its other efforts, FHWA is working on the development of a comprehensive and crosscutting roadmap on intersections.

Although crashes, injuries, and fatalities at intersections are not entirely avoidable, much can be done to improve the current situation. Thanks to the innovative activities and cutting-edge research being carried out by FHWA and its partners, American motorists, cyclists, and pedestrians today and in the future can look forward to safer intersections.

"Safety is a shared responsibility among engineers, law enforcement officials, and highway users," notes Rudy Umbs. "Everybody must do his or her part to save lives. Engineers must use the latest technology and practices. Enforcement must ensure that laws are obeyed. Highway users—motorists, bicyclists, and pedestrians—must be aware of ever-changing conditions and act sensibly, courteously, and sanely."


Joe G. Bared is a highway research engineer in FHWA's Office of Research and Development. He manages research contracts and conducts staff research in the areas of safety and the operational effects of design. He has a doctorate in transportation engineering from the University of Maryland, and he is a registered professional engineer.

Patrick Hasson is the safety and operations team leader in FHWA's Midwestern Resource Center. In this position, he is involved in regional, national, and international projects in the areas of geometric design, Intelligent Transportation Systems, and safety engineering, education, and enforcement. He is the national coordinator for the FHWA Stop Red Light Running Program and is actively involved in the intersection safety programs. He holds a B.S. in engineering from the University of Maryland and an M.S. in engineering from Cornell University.

Fred N. Ranck is the safety/geometrics engineer for FHWA's Safety Team of Excellence, providing technical support to the FHWA Divisions and States across the country; member of FHWA's MUTCD team with responsibility for Part 2; member of FHWA's Intersection Safety Team and Work Zone Policy Team. He is a licensed professional traffic operations engineer and professional engineer in Illinois. Ranck has a B.A. in physics and a B.S. and M.S. in civil engineering from the University of Illinois.

Hari Kalla is a transportation specialist for FHWA in Washington, DC. He leads the intersection safety program area in FHWA's Office of Safety. He received a master's degree in civil engineering from State University of New York and is a registered professional engineer in New York.

Robert A. Ferlis is a research engineer and team leader for enabling technology in FHWA's Office of Operations Research and Development. He has served as the crosscutting coordinator of the IVI Program since 1998, where he supports research in vehicle-highway cooperation and currently is responsible for managing the IVI research in intersection collision avoidance systems. He received a B.S. in systems engineering from the University of Illinois and a masters in civil engineering from Northwestern University.

Michael S. Griffith is the technical director of FHWA's Office of Safety Research and Development. He chairs the committee for a new FHWA study evaluating the safety effectiveness of red-light running cameras. Griffith is also active in a number of national initiatives such as the Research and Technology National Partnership Initiative and the Highway Safety Manual.

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