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Publication Number: FHWA-HRT-06-129
Date: February 2006

Pedestrian and Bicyclist Intersection Safety Indices

FHWA Contact: Ann Do, HRDS-06, 202–493–3319, ann.do@fhwa.dot.gov

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OVERVIEW

The Pedestrian and Bicycle Intersection Safety Indices (Ped ISI and Bike ISI) are a set of models that enable users to identify intersection crossings and intersection approach legs that should be the greatest priority for undergoing indepth pedestrian and bicycle safety assessment. Using observable characteristics of an intersection crossing or approach leg, such as number of lanes and traffic volume, the tool produces a safety index score, with higher scores indicating greater priority for an indepth safety assessment. Each leg of an intersection may have different characteristics affecting pedestrian or bicyclist safety; therefore, the tool is intended to provide a rating of the safety of an individual crossing (Ped ISI) or approach leg (Bike ISI) rather than evaluating the intersection as a whole. A practitioner can use the tool to develop a prioritization scheme for a group of pedestrian crossings or bicyclist approaches. This method enables the practitioner to prioritize and proactively address sites that are the most likely to be a safety concern for pedestrians or bicyclists without having to wait for crashes to occur.

 

DEVELOPMENT

Researchers developed the Ped ISI and Bike ISI based on safety ratings, or expert opinion of the safety of a site, and observed behaviors, or observed interactions between pedestrians and motorists or bicyclists and motorists. These measures enabled the researchers to use a multifaceted approach to determine the relative safety of a pedestrian crossing or bicycle approach leg.

To develop the Ped ISI and Bike ISI models, researchers studied 68 pedestrian crossings at signalized and unsignalized intersections in Miami, FL, Philadelphia, PA, and San Jose, CA, and 67 bicycle approaches at signalized and unsignalized intersections in Eugene, OR, Gainesville, FL, Philadelphia, PA, and Portland, OR.

 

SAFETY MEASURE: RATINGS

To develop the safety ratings, evaluators knowledgeable about pedestrian and bicyclist issues viewed illustrations and videos of the pedestrian crossings and bicycle approaches, as shown in figure 1, and rated the sites according to their perceived level of safety for a pedestrian or bicyclist. Researchers asked the evaluators to view the illustration and video as if they themselves were pedestrians crossing at the crosswalk or bicyclists approaching the intersection. The evaluators then rated the sites on a scale of one (most safe) to six (least safe), according to their sense of safety and comfort.

Figure 1. Illustration and Photo. An example of an illustration and a screen capture from the video shown to evaluators. This illustration shows the intersection of two roads, Allegheny, which runs north to south, and Aramingo, which runs west-east. Allegheny is a four lane road with bike lanes in both directions and parallel onstreet parking on both sides of the street. Aramingo is a two lane road with bike lanes in both directions and parallel onstreet parking on both sides of the street. The illustration shows two cameras positioned along the sidewalk parallel to Allegheny that capture the north-south crosswalk on the west side of the intersection. Camera 1 is on the west side of Allegheny, several yards north of the intersection. Camera 2 is on the west side of Allegheny, several yards south of the intersection.

This photo is the illustration shows a clip of the video filmed by camera 1.

Figure 1. An example of an illustration and a screen capture from the video shown to evaluators.

 

SAFETY MEASURE: OBSERVED BEHAVIORS AT INTERSECTIONS

To evaluate observed behaviors, researchers videotaped each site and watched the tapes to record the behavior of pedestrians and bicyclists when they interacted with motorists. Recorded behaviors included changes in speed or direction by a pedestrian, bicyclist, or motorist in response to the presence of another party. The researchers, for example, would record instances when a pedestrian stopped before or during a crossing because of an oncoming vehicle or when a right-turning vehicle slowed down or stopped to avoid a bicyclist. These interactions included avoidance maneuvers (any change in speed or direction) and conflicts (sudden change in speed or direction). In total, the researchers observed 1,898 bicyclist-motorist interactions and 1,095 pedestrian-motorist interactions.

 

PED ISI

As shown in table 1, the Ped ISI model consists of one equation that determines the safety index score for a single pedestrian crossing.

 

Table 1. The Ped ISI model is shown.

Ped ISI = 2.372 – 1.867SIGNAL – 1.807STOP + 0.335THRULns + 0.018SPEED + 0.006( MAINADT*SIGNAL) + 0.238COMM

where:

Ped ISI

Safety index value

SIGNAL

Signal-controlled crossing

0 = no

1 = yes

STOP

Stop-sign-controlled crossing

0 = no

1 = yes

THRULNS

Number of through lanes on street being crossed (both directions)

1, 2, 3,...

SPEED

85th percentile speed of street being crossed

Speed (miles per hours (mph))

MAINADT

Main street traffic volume

Average Daily Traffic (ADT) (in thousands)

COMM

Predominant land use in surrounding area is commercial development (i.e., retail, restaurants)

0 = not predominantly commercial area

1 = predominantly commercial area

 

BIKE ISI

As shown in table 2, the Bike ISI consists of three equations. Each equation determines the safety index score for a single bicycle movement, either straight through, left turn, or right turn.

 

Table 2. The Bike ISI model is shown.

Through

Bike ISI = 1.13 + 0.019MainADT + 0.815MainHISPD + 0.650TurnVeh + 0.470(RTLanes *BL) + 0.023(CrossADT*NoBL) + 0.428(Signal*NoBL) + 0.200 Parking

Right Turn

Bike ISI = 1.02 + 0.027MainADT + 0.519RTCross + 0.151CrossLNS + 0.200Parking

Left Turn

Bike ISI = 1.100 + 0.025MainADT + 0.836BL + 0.485Signal + 0.736(MainHISpd *BL) + 0.380(LTCross*NoBL) + 0.200Parking

where:

Bike ISI

Safety index value

BL

Bike lane presence

0 = NONE or Wide Curb Lane (WCL)

1 = Bike Lane (BL) or Bike Lane Crossover (BLX)

CrossADT

Cross street traffic volume

ADT (in thousands)

CrossLNS

Number of through lanes on cross street

1, 2,

LTCross

Number of traffic lanes for cyclists to cross to make a left turn

0, 1, 2,

MainADT

Main street traffic volume

ADT (in thousands)

MainHISPD

Main street speed limit ≥ 35 mph

0 = no

1 = yes

NoBL

No bike lane present

0 = BL or BLX

1 = NONE or WCL

Parking

Onstreet parking on main street approach

0 = no

1 = yes

RTCross

Number of traffic lanes for cyclists to cross to make a right turn

0, 1, 2,...

RTLanes

Number of right turn traffic lanes on main street approach

0, 1, 2,...

Signal

Traffic signal at intersection

0 = no

1 = yes

TurnVeh

Presence of turning vehicle traffic across the path of through cyclists

0 = no

1 = yes

 

USER GUIDE

The Pedestrian and Bicyclist Intersection Safety Indices: User Guide (FHWA-HRT-06-130) is a companion document to the research report that provides the practitioner the information needed to implement the Ped ISI and Bike ISI. It covers the data needs, presents the models, and provides examples of how to use the Ped ISI and Bike ISI. It also includes quick reference tables, such as the one shown in figure 2, that enable users to determine a safety index value for a site without the need for a calculator or computer.

Figure 2. Chart. Figure 2. An example of a quick reference table found in the User Guide. The image is a demonstration of how to find the safety index value of an intersection by using a quick reference table found in the User Guide. The image shows a portion of the table and two arrows pointing from the appropriate row and column to the intersecting cell with the corresponding safety index value. For this example, the safety index value obtained from the table is 2.4.

Figure 2. An example of a quick reference table found in the User Guide.

For more details on the underlying research and model development, see the final research report:

Carter, Daniel L., William W. Hunter, Charles V. Zegeer, J. Richard Stewart, and Herman F. Huang, Pedestrian and Bicyclist Intersection Safety Indices: Final Report, Federal Highway Administration, Washington, DC, Report FHWA-HRT-06-125, 2006.

Researcher—This study was performed by the University of North Carolina Highway Safety Research Center, Chapel Hill, NC.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct distribution is being made to the Divisions and Resource Center.

Availability—The publication from which this TechBrief was developed, Pedestrian and Bicyclist Intersection Safety Indices: Final Report, (FHWA-HRT-06-125), will be available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161. A limited number of copies will be available from the Research and Technology Product Distribution Center, HRTS-03, FHWA, 9701 Philadelphia Court, Unit Q, Lanham, MD 20706, 301 –577–0818 (telephone), 301–577–1421 (fax).

Key Words—pedestrian, bicycle, intersection, safety, index

Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

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