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Pedestrian and Bicyclist Intersection Safety Indices

User Guide

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CHAPTER 3. PEDESTRIAN AND BICYCLE INTERSECTION SAFETY INDICES

Below are the model equations for Ped ISI and Bike ISI. The user should keep in mind that these tools were developed to evaluate the safety of an individual crosswalk or approach leg, not the intersection as a whole. Thus, if a standard 4-leg intersection is to be evaluated, there will be 4 pedestrian safety scores, 1 for each crossing, and 12 bicycle safety scores, 3 for each leg. Higher index values indicate areas of greater safety concern. Those locations with higher index values should be prioritized for more indepth safety evaluation.

NOTE: The user may choose to average the index values for each leg together to form an index value for an entire intersection. The decision of whether this method is appropriate will depend on the user's knowledge of the area being evaluated and the understanding of how the information will be used.

Data Required

The following is a list of data required for each safety index (main street defined as the street containing the crossing or approach of interest, not the street with the higher functional class or higher traffic volume):

Ped ISI

• Type of traffic control for leg of crossing (signal, stop sign, or neither).
• Number of through vehicle lanes on main street (total through lanes in both directions).
• Eighty-fifth percentile traffic speed on main street.
• Average daily traffic (ADT) of main street.
• Predominant development type surrounding the intersection (commercial or not commercial).

Bike ISI

• Presence of bicycle lane on main street.
• ADT on main and cross streets.
• Number of through vehicle lanes on cross street.
• Number, type, and configuration of traffic lanes on main street approach.
• Speed limit on main street.
• Presence of onstreet parking on main street approach.
• Type of traffic control on approach of interest (signal or no signal).

Ped ISI

The Ped ISI model consists of one equation that determines the safety index score for a single pedestrian crossing. The model is presented in Table 1 below. A detailed description of the variables follows the table. Figure 5 illustrates a pedestrian crossing.

Table 1. Ped ISI model and variable descriptions.

Figure 5. Illustration of pedestrian crossing.

Variable Descriptions

SIGNAL (Signal Control)

This variable is "1" if movements of vehicles and pedestrians at the crossing of interest are controlled by a traffic signal.

STOP (Stop Control)

This variable is "1" if vehicle traffic on the leg with the crossing of interest must stop for a stop sign.

THRULNS (Through Lanes)

This variable is the number of through lanes on the street with the crossing of interest, not including exclusive turn lanes. However, since crosswalks that cross the stem of T-intersection do not have through lanes to cross, turning lanes are included in the count for THRULNS for these crosswalks.

SPEED (Vehicle Speed)

This variable is the 85th percentile speed in mi/h of free-flowing vehicles on the street with the crossing of interest. If speed data are obtained for a street on both sides of the intersection (both approaches), the values should be averaged to provide the value for the Ped ISI model. If actual speed data are not available, the user may use the speed limit or an estimate of the 85th percentile speed.

MAINADT (Main Street ADT)

This variable is the ADT volume (in thousands) of the street with the crossing of interest (main street). This is the total traffic in both directions.

COMM (Commercial Development)

This variable is "1" if the predominant land use of the surrounding area is commercially developed. Commercial development is defined as retail shops, banks, restaurants, gas stations, and other businesses that sell to the general public.

Bike ISI

The Bike ISI consists of three equations. Each equation determines the safety index score for a single bicycle movement, either straight through, right turn, or left turn. The models are presented in Table 2 below. A detailed description of the variables follows the table. Figure 6 illustrates a bicycle approach.

Table 2. Bike ISI models and variable descriptions.

Figure 6. Illustration of bicycle approach.

Variable Descriptions

BL (Bike Lane)

This variable is "1" if there is a bike lane on the approach (defined as BL or BLX in Figure 7). Variable is "0" if there is no bicycle lane ("None") or simply a wide curb lane ("WCL"). In some cases, there may be a paved shoulder that, while not marked for bicycles, might serve as a de facto bike lane. If this paved shoulder is narrow (i.e., 0.3 to 0.9 meter (m) (1 to 3 feet (ft)), define BL as "0." If the paved shoulder is relatively wide (i.e., 1.2 m (4 ft) or greater), define BL as "1."

Figure 7. Bicycle facility types.

CROSSADT (Cross Street ADT)

This variable is the average daily traffic volume (in thousands) of the street intersecting the approach leg of interest. This is the total traffic in both directions.

CROSSLNS (Cross Street Through Lanes)

This variable is the number of through lanes on the street intersecting the approach leg of interest.

LTCROSS (Lanes to Cross for Left Turn)

This variable is the number of traffic lanes that a bicyclist on the approach of interest must cross and/or enter to make a left turn at the intersection. This variable assumes that the bicyclist is riding in a bike lane (either right-side or left-side bike lane) or on the right-hand side of the road if no bike lane is present. If this variable is not applicable (e.g., no left turn possible or permitted), the value of RTCROSS would be zero. See Figure 8 for example illustrations.

LTCROSS = 1 a. A bicyclist* in the bike lane will need to enter only one lane to make a left turn.	LTCROSS = 1 b. A bicyclist* (assumed to be riding on the right hand side of the road) must enter only one lane to make a left turn.
LTCROSS = 2 c. A bicyclist* in the bike lane will need to cross one lane and enter one lane (total of two) to make a left turn.	LTCROSS = 3 d. A bicyclist* (assumed riding in the bike lane) will need to cross two lanes and enter one lane (total of three) to make a left turn.
* Bicyclist approaches the intersection from the bottom leg in these examples.

Figure 8. Examples of LTCROSS values.

MAINADT (Main Street ADT)

This variable is the ADT volume (in thousands) of the approach leg of interest. This is the total traffic in both directions.

MAINHISPD (Main Street Speed Limit Over 35)

This variable is "1" if the speed limit of the leg of interest is 56.3 km/h (35 mi/h) or higher.

NOBL (No Bike Lane)

This variable is "1" if there is no bike lane on the approach (defined as "None" or "WCL" in Figure 7 above). Variable is "0" if there is a bicycle lane ("BL" or "BLX").

PARKING (Onstreet Parking)

This variable is "1" if there is onstreet parking on the approach of interest.

RTCROSS (Lanes to Cross for Right Turn)

This variable is the number of traffic lanes that a bicyclist on the approach of interest must cross to make a right turn at the intersection. This variable assumes that the bicyclist is riding in a bike lane (either right-side or left-side bike lane) or on the right-hand side of the road if no bike lane is present. Under these assumptions, the value of RTCROSS will typically be zero. If the bike lane is a bike lane crossover (BLX in Figure 7 above), it is assumed that the bicyclist (knowing that the bicyclist was going to make a right turn), left the bike lane and held to the right shoulder of the road. In this case, the value of RTCROSS would be zero. If this variable is not applicable (e.g., no right turn possible or permitted), the value of RTCROSS would be zero. See Figure 9 for example illustrations.

RTCROSS = 0 a. A bicyclist* (assumed to be riding on the right hand side of the road) will not need to cross or enter any lanes to make a right turn.	RTCROSS = 0 b. A bicyclist* (assumed to have left the bike lane and held to the right shoulder) will not need to cross or enter any lanes to make a right turn.
RTCROSS = 3 c. A bicyclist* (assumed to be riding in the left-side bike lane) will need to cross two lanes and enter one lane (total of three) to make a right turn.
* Bicyclist approaches the intersection from the bottom leg in these examples.

Figure 9. Examples of RTCROSS values.

RTLANES (Right-Turn Lanes)

This variable is the number of exclusive right-turn traffic lanes on the leg of interest.

SIGNAL (Signalized Intersection)

This variable is "1" if the intersection is controlled by a traffic signal.

TURNVEH (Turning Vehicles)

This variable is "1" if it would be reasonable to assume that the path taken by through cyclists at the intersection is regularly crossed by vehicles turning right from the main approach to the cross street. A lack of turning traffic would occur with a bike lane crossover, since turning motorists would have merged over already. It could also occur with one-way cross streets, if the one-way flow prevents motorists from turning in front of through bicyclists. See Figure 10 for example illustrations.

TURNVEH = 1 a. The path of through bicyclists can be intersected by vehicles turning right from the main approach onto the cross street.	TURNVEH = 0 b. The path of through bicyclists will not be intersected by vehicles turning right from the main approach onto the cross street (cross street is one-way to the left).
TURNVEH = 0 c. The path of through bicyclists (assumed to be in the bike lane when they reach the intersection) will not be intersected by vehicles turning right from the main approach onto the cross street.
* Bicyclists approach the intersection from the bottom leg in these examples.

Figure 10. Examples of TURNVEH values.

FHWA-HRT-06-130