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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

Bike ISI

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.

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

where:

Ped ISI

Safety index value (pedestrian)

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

Eighty-fifth percentile speed of street being crossed

Speed in miles per hour

MAINADT

Main street traffic volume

ADT in thousands

COMM

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

0 = not predominantly commercial area

1 = predominantly commercial area

Figure 5. Illustration of pedestrian crossing.

Figure 5. Illustration of Pedestrian Crossing. The illustration shows a generic intersection of two roads, Main Street and Cross Street. Cross Street runs north-south and Main Street runs west-east. Both streets have one travel lane in each direction. A box reading "Crossing of Interest" is pointing to the north-south crosswalk on the east side of the intersection. Therefore, the crossing of interest is the one perpendicular to the direction of travel on Main Street and parallel to the direction of travel on Cross Street.

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.

Through

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

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 values (through, right, left)

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 ≥ 56.3 km/h (35 mi/h)

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

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

Figure 6. Illustration of bicycle approach.

Figure 6. Illustration of Bicycle Approach. The illustration shows a generic intersection of two roads, Main Street and Cross Street. Cross Street runs north-south and Main Street runs west-east. Both streets have one travel lane in each direction. The section of Main Street approaching the intersection from the east is labeled "Approach of Interest." Therefore, the approach of interest is along Main Street and perpendicular to Cross Street.

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.

A. None-no specific bicycle facility. The illustration shows a two-lane road approaching the intersection with another road. Both lanes have a width of less than 4.3 meters (14 feet). B. WCL-wide curb lane. The illustration shows the same two-lane road with lane width greater than or equal to 4.3 meters (14 feet). C. BL-bike lane shows the same two-lane road with a separate bicycle lane to the right of the right lane. D. BLX-bike lane crossover shows the same road with the separate bike lane, but shows the bike lane continuing straight through the intersection while a right turn lane crosses through the bike lane. The lines delineating the bike lane are dotted where the right turn lane crosses though.

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.

Figure 8. Examples of LTCROSS values.
A. A bicyclist in the bike lane will need to enter only one lane to make a left turn.The illustration shows the intersection of two two-lane roads, Pearl and 5th. Pearl runs north-south while 5th runs west-east. There are bike lanes in both directions of 5th on both sides of the intersection. There are no specific bicycle facilities on Pearl. The bike lane on 5th approaching the intersection from the west crosses over the right turn lane just before the intersection. The bicyclist in this example approaches the intersection from the west on 5th in the bike lane. The L-T-CROSS value for this picture is 1.

LTCROSS = 1

a. A bicyclist* in the bike lane will need to enter only one lane to make a left turn.

 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.The illustration shows the intersection of two two-lane roads, Main Street and Cotton Street. Main Street runs west-east and Cotton Street runs north-south. There are no specific bicycle facilities on either road. The bicyclist in this example approaches the intersection along Main Street from the west. The L-T-CROSS value for this picture is 1.

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.
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. The illustration shows the intersection of two two-lane roads, Agate and 15th. Agate runs north-south while 15th runs west-east. Agate has separate left-turn lanes in both directions. There is a bike lane on the west side of Agate. There are no specific bicycle facilities on 15th. The bicyclist in this example approaches the intersection along Agate from the north. The L-T-CROSS value for this picture is 2.

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.

 D. A bicyclist (assumed to be riding in the bike lane) will need to cross two lanes and enter one lane (total of three) to make a left turn. The illustration shows the intersection of two one-way roads, Chestnut and 33rd. Chestnut is a three-lane road running east with a bike lane on the south side of the road (to the right of the travel lanes). Thirty-third is a two-lane road running north with a bike lane on the east side of the road (to the right of the travel lanes). The bicyclist in this example approaches the intersection along Chestnut in the bike lane. The L-T-CROSS value for this picture is 3.

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.
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.

Figure 9. Examples of RTCROSS values.
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. The drawing shows the intersection of two two-lane roads, Green Lane and Main Street. Main Street runs west-east while Green Lane runs north-south. The bicyclist in this example approaches the intersection along Main Street from the east, turning right onto Green Lane. The R-T-CROSS value for this picture is 0.

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.

 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. The top right picture shows the intersection of two two-lane roads, South Street and 33rd Street. South Street runs west-east while 33rd Street is a one-way road running north. There are bike lanes on both sides of South Street. The bike lane on South Street approaching the intersection from the east crosses over the right-turn lane. There is a bike lane on 33rd Street north of the intersection on the east side of the road. The bicyclist in this example approaches the intersection on South Street from the east and riding in the bike lane. The R-T-CROSS value for this picture is 0.

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.

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. The bottom picture shows the intersection of two one-way roads, Pearl and 11th. Pearl is a two-lane road running south while 11th is a three-lane road running west. There is a bike lane on the east side of Pearl (to the left of traffic). The R-T-CROSS value for this picture is 3.

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.

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.

Figure 10. Examples of TURNVEH values.
A. The path of through bicyclists can be intersected by vehicles turning right from the main approach onto the cross street shows the intersection of two roads, Hawthorne and 7th. Hawthorne is a one-way, three-lane road running east while 7th is a two-lane road running north-south. There is a bike lane on the south side of Hawthorne (to the right of the travel lanes). The bicyclist in this example approaches the intersection along Hawthorne from the west in the bike lane. The TURN-V-E-H value for this picture is 1.

TURNVEH = 1

a. The path of through bicyclists can be intersected by vehicles turning right from the main approach onto the cross street.

 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) shows the intersection of two one-way roads, 11th and Pearl. Eleventh is a three-lane road running west while Pearl is a two-lane road running south. There is a bike lane on the north side of 11th (to the right of the travel lanes). The bicyclist in this example approaches the intersection along 11th. The TURN-V-E-H value for this picture is 0.

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).
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 shows the intersection of two two-lane, one-way streets, Pearl and 13th. Thirteenth runs east while Pearl runs south. There is a bike lane on the south side of 13th Street (to the right of the travel lanes). The bike lane crosses over the right-turn lane just before the intersection. The TURN-V-E-H value is 0.

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.

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