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Publication Number: FHWA-HRT-06-130
Date: April 2007

Pedestrian and Bicyclist Intersection Safety Indices

User Guide

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CHAPTER 4. EXAMPLES OF PED ISI AND BIKE ISI APPLICATIONS

The following section provides several examples which illustrate how to apply Ped ISI and Bike ISI at various sites. Each example has several site photos and a list of intersection characteristics. The example calculation of the safety index value is done with the spreadsheet calculators that accompany the User Guide. An example of using the quick reference tables is performed with the pedestrian example 1 and bicycle example 1.

Pedestrian Example

The example for Ped ISI is a four-leg, signalized intersection in a mostly residential area. The crossing of interest is on the southwest leg. Figure 11, Figure 12, and Figure 13 show onstreet and overhead photos of the site, with the crossing of interest pointed out with a white arrow.

 

Figure 11. Photograph.  Crosswalk view of pedestrian example intersection. This is one of three photographs of the same intersection. This picture, from the street level, shows the signalized intersection of two roads, a four-lane main road and a two-lane cross street in a predominantly residential area. There is a marked, signalized crosswalk across the main road from one of the corners of the intersection.

Figure 11. Crosswalk view of pedestrian example intersection.

 

Figure 12. Photograph. Diagonal view of pedestrian example intersection. This is one of three photographs of the same intersection. This picture, from the street level, shows the signalized intersection of two roads, a four-lane main road and a two-lane cross street in a predominantly residential area. This picture shows the same crosswalk as in Figure 11 from farther down the main street (the crosswalk is marked by an arrow pointer).

Figure 12. Diagonal view of pedestrian example intersection.

 

Figure 13. Photograph. Overhead view of pedestrian example intersection (image courtesy of the United States Geological Survey). This is an aerial view of the same intersection as in Figures 11 and 12. In this picture the crosswalk is marked by an arrow pointer.

Figure 13. Overhead view of pedestrian example intersection (image courtesy of the United States Geological Survey).

This crossing location has the following characteristics:

  • Signalized intersection.
  • Four through lanes on the main road (two in each direction).
  • Eighty-fifth percentile speed on the main road is 67.6 km/h (42 mi/h).
  • Main road ADT is 22,000 vehicles per day.
  • Surrounding area is residential.

Once these characteristics are entered into the spreadsheet calculator, the resulting Ped ISI value is 2.7 (Figure 14).

 

Figure 14. Image. Spreadsheet Calculation of Ped I-S-I Value. The image is a screenshot showing the Excel spreadsheet calculation of the safety index value for the same intersection shown in Figures 11, 12, and 13. The appropriate data has been filled into the spreadsheet in order to calculate the Pedestrian I-S-I value. In this example, the spreadsheet calculator produces a safety index value of 2.7.

Figure 14. Spreadsheet calculation of Ped ISI value.

Using the Ped ISI model equation, the calculation is as follows:

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

Ped ISI = 2.372−1.867*1−1.807*0 + 0.335*4 + 0.018*42 + 0.006(22*1) = 0.238*0

Ped ISI = 2.7

Notice that the ADT value must be entered in thousands (i.e., 22 instead of 22,000) for the equation. The spreadsheet calculator allows the user to enter the ADT as a whole value. Another way to determine the Ped ISI value is to go directly to the quick reference tables of Ped ISI values in Appendix B. These tables are provided for various combinations of traffic control and area type. For the example above, Table 9 in Appendix B corresponds to a signalized crossing in a noncommercial area (Figure 15). Going into that table with 4 through lanes, 85th percentile speed of 67.6 km/h (42 mi/h) (use the column of the nearest value, i.e., 64.4 km/h (40 mi/h)), and 22,000 ADT (use the row with 20,000 ADT), the Ped ISI value is 2.7.

Figure 15. Image. Quick Reference Table-Pedestrian (Signalized and Noncommercial Area). The image is a demonstration of how to find the Ped I-S-I value of the same intersection shown in Figures 11, 12, and 13 by using the quick reference table. 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 Ped ISI value. For this example, as previously calculated, the Ped I-S-I value obtained from the Quick Reference Table is 2.7.

1 mi/h = 1.6 km/h

Figure 15. Quick reference table—pedestrian (signalized and noncommercial area).

 

Bicycle Example 1

Example 1 for Bike ISI is the westbound approach of a four-leg, signalized intersection. Figure 16, Figure 17, and Figure 18 show onstreet and overhead photos of the approach of interest (indicated by arrow).

 

Figure 16. Photograph.  Street view of bicycle example 1. This is one of three photographs of the same intersection. This picture, from the street level, shows the signalized intersection of two roads. The main approach road is a two-lane road with separate left- and right-turn lanes approaching the intersection. The crossing street is a four-lane road with a separate left-turn lane.

Figure 16. Street view of bicycle example 1.

 

Figure 17. Photograph. Street view of bicycle example 1. This is one of three photographs of the same intersection, also from the street level and from the east, but closer to the intersection.

Figure 17. Street view of bicycle example 1.

 

Figure 18. Photograph. Overhead photo of bicycle example 1 (image courtesy of the United States Geological Survey). This picture is an aerial view of the same intersection shown in Figures 16 and 17. An arrow pointer marks the approach to the intersection from the east.

Figure 18. Overhead photo of bicycle example 1 (image courtesy of the United States Geological Survey).

 

This approach has the following characteristics:

  • Signalized intersection.
  • Speed limit of 56.3 km/h (35 mi/h) on the main road.
  • One exclusive right-turn lane and one exclusive left-turn lane on the approach.
  • No bicycle facility on the approach.
  • No onstreet parking on the approach.
  • Main road ADT is 17,000 vehicles per day.
  • Cross street ADT is 28,000 vehicles per day.
  • Four through lanes on the cross street.

Once these characteristics are entered into the spreadsheet calculator, the resulting Bike ISI values are 4.0 for through movement, 2.1 for right turns, and 3.2 for left turns (Figure 19).

 

Figure 19. Image. Spreadsheet Calculation of Safety Index Values for Bicycle Example 1. The image is a screenshot showing the Excel spreadsheet calculation of the safety index values for the previous intersection, shown in Figures 16, 17, and 18. The appropriate data have been filled into the spreadsheet in order to calculate the Bicycle I-S-I values. In this example, the spreadsheet calculator produces a safety index Through value of 4.0, a safety index right turn value of 2.1, and a safety index left-turn value of 3.2.

1 mi/h = 1.6 km/h

Figure 19. Spreadsheet calculation of safety index values for bicycle example 1.

Using the Bike ISI model equations, the calculations are as shown in Table 3:

Table 3. Bike ISI model equations.

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

Bike ISI = 1.13 + 0.019*17 + 0.815*1 + 0.650*1+ 0.470(1*0) + 0.023(28*1 ) + 0.428(1*1) + 0.200*0

Bike ISI = 4.0

Right Turn

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

Bike ISI = 1.02 + 0.027*17 + 0.519*0 + 0.151*4 + 0.200*0

Bike ISI = 2.1

Left Turn

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

Bike ISI = 1.100 + 0.025*17 + 0.836*0 + 0.485*1 + 0.736(1*0) + 0.380(3*1) + 0.200*0

Bike ISI = 3.2

 

Using the quick reference tables for bicycle example 1, the following results are found:

"Through" safety index value

Since there are four "through" bicycle tables (Tables 14, 15, 16, and 17 in Appendix B), it is necessary to start with Table 15 for "Signalized Intersection" and "No Bike Lane" (shown here in Figure 20 , full-size table available in Appendix B). Across the top of the table, the user would select the column for "35 mph or more," "No parking," "1 Right-Turn Lane," and "Yes" for potential turning vehicles. Down the side of the table, it is necessary to interpolate the Main and Cross ADT values. The table shows that the through safety index value will lie between 3.7/3.9 and 3.9/4.1 (the exact calculation performed in Figure 19 above shows that the actual value is 4.0).

 

Figure 20. Image. Quick Reference Table-Bicycle Through (Signalized With No Bike Lane). This image is a demonstration of how to find the Bicycle I-S-I Through value of this intersection using the quick reference table. The image shows a portion of the table and three arrows pointing from the appropriate rows and column to the intersecting cells with the corresponding Bicycle I-S-I Through value. For this example the Through value will lie between 3.7/3.9 and 3.9/4.1. The calculated value from the spreadsheet shown in Figure 19 was 4.0.

1 mi/h = 1.6 km/h

Figure 20. Quick reference table—bicycle through (signalized with no bike lane).

"Right turn" safety index value

There is only one table for right turn safety index values, Table 18, (shown here in Figure 21, full-size table available in Appendix B). Across the top of the table, the user would select the column for "4 Cross Street Through Lanes," "No" onstreet parking, and "0" RT Cross Lanes (lanes to cross to make a right turn). Down the side of the table, it is necessary to interpolate the Main ADT values. The table shows that the through safety index value will lie between 1.9 and 2.2 (the exact calculation performed in Figure 19 above shows that the actual value is 2.1).

Figure 21. Image. Quick Reference Table-Bicycle Right Turn. This image is a demonstration of how to find the Bicycle ISI right-turn value of this intersection using the quick reference table. 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 Bicycle I-S-I right-turn value. For this example the right-turn value will lie between 1.9 and 2.2. The calculated value from the spreadsheet shown in Figure 19 was 2.1

Figure 21. Quick reference table—bicycle right turn.

"Left turn" safety index value

Since there are four "left turn" bicycle tables (Tables 19, 20, 21, and 22 in Appendix B), it is necessary to start with Table 20 for "Signalized Intersection" and "No Bike Lane" (shown here in Figure 22, full-size table available in Appendix B). Across the top of the table, the user would select the column for "35 mph or more," "3" LT Cross lanes (lanes to cross to make a left turn), and "No" onstreet parking. Down the side of the table, it is necessary to interpolate the Main ADT values. The table shows that the through safety index value will lie between 3.0 and 3.2 (the exact calculation performed in Figure 19 above shows that the actual value is 3.2).

Figure 22. Image. Quick Reference Table-Bicycle Left Turn (Signalized with No Bike Lane). This image is a demonstration of how to find the Bicycle I-S-I left-turn value of this intersection using the quick reference table. 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 Bicycle I-S-I left-turn value. For this example the left-turn value lies between 3.0 and 3.2. The calculated value from the spreadsheet shown in Figure 19 was 3.2.

1 mi/h = 1.6 km/h

Figure 22. Quick reference table—bicycle left turn (signalized with no bike lane).

 

Bicycle Example 2

Example 2 for Bike ISI is the westbound approach of a three-leg, signalized intersection. Figure 23, Figure 24, and Figure 25 show onstreet and overhead photos of the approach of interest (indicated by arrow).

 

Figure 23. Photograph.  Street view of bicycle example 2. This is one of three photographs of the same intersection. This picture, from the street level, shows a three-leg, signalized intersection of two roads. The main approach road is a two-lane road with a separate left-turn lane approaching the intersection. The secondary street that Ts into the main road is a two-lane road.

Figure 23. Street view of bicycle example 2.

 

Figure 24. Photograph. Street view of bicycle example 2. This is one of three photographs of the same intersection. This picture, also from the street level, shows the same approach to the intersection along the main road from the east as in Figure 23, but closer to the intersection.

Figure 24. Street view of bicycle example 2.

 

Figure 25. Photograph. Overhead view of bicycle example 2 (image courtesy of the United States Geological Survey). This picture is an aerial view of the same intersection as in Figures 23 and 24. An arrow pointer marks the approach to the intersection from the east.

Figure 25. Overhead view of bicycle example 2 (image courtesy of the United States Geological Survey).

 

This approach has the following characteristics:

  • Signalized intersection.
  • T-intersection (no right turn possible on approach of interest).
  • Speed limit of 48.3 km/h (30 mi/h) on the main road.
  • One exclusive left-turn lane on the approach.
  • Bicycle lane on the approach.
  • No onstreet parking on the approach.
  • Main road ADT is 10,000 vehicles per day.
  • Cross street ADT is 6,000 vehicles per day.
  • Two through lanes on the cross street.

Once these characteristics are entered into the spreadsheet calculator, the resulting Bike ISI values are 1.3 for through movements, 1.6 for right turns, and 2.7 for left turns (Figure 26). These values can also be obtained from Tables 14, 18, and 19 in Appendix B.

 

Figure 26. Image. Spreadsheet Calculation of Bike I-S-I Values for Bicycle Example 2. The image is a screenshot showing the Excel spreadsheet calculation of the safety index values for the intersection shown in Figures 23, 24, and 25. The appropriate data have been filled into the spreadsheet in order to calculate the Bicycle I-S-I values. In this example, the spreadsheet calculator produces a safety index Through value of 1.3, a safety index Right-turn value of 1.6, and a safety index left-turn value of 2.7.

1 mi/h = 1.6 km/h

Figure 26. Spreadsheet calculation of bike ISI values for bicycle example 2.

 

Bicycle Example 3

Example 3 for Bike ISI is the westbound approach of a four-leg, signalized intersection. Figure 27, Figure 28, and Figure 29 show onstreet and overhead photos of the approach of interest (indicated by arrow).

Figure 27. Photograph. Street view of bicycle example 3. This is one of three photographs of the same intersection. This picture, from the street level, shows a four-leg, signalized intersection of two roads. The main approach road is a four-lane road with a separate left-turn lane approaching the intersection and parallel onstreet parking on both sides of the street. The crossing street is a four-lane road with separate left-turn lanes.

Figure 27. Street view of bicycle example 3.

 

Figure 28. Photograph. Street view of bicycle example 3. This is one of three photographs of the same intersection. This picture, also from the street level, is from the same direction as Figure 27, but closer to the intersection.

Figure 28. Street view of bicycle example 3.

 

Figure 29. Photograph. Overhead view of bicycle example 3 (image courtesy of the United States Geological Survey). This is an aerial view of the same intersection as in Figures 27 and 28. An arrow pointer marks the approach to the intersection from the east.

Figure 29. Overhead view of bicycle example 3 (image courtesy of the United States Geological Survey).

This approach has the following characteristics:

  • Signalized intersection.
  • Speed limit of 56.3 km/h (35 mi/h) on the main road.
  • One exclusive left-turn lane on the approach.
  • No bicycle facility on the approach.
  • Onstreet parking on the approach.
  • Main road ADT is 17,000 vehicles per day.
  • Cross street ADT is 18,000 vehicles per day.
  • Four through lanes on the cross street.

Once these characteristics are entered into the spreadsheet calculator, the resulting Bike ISI values are 4.0 for through movements, 2.3 for right turns, and 3.4 for left turns (Figure 30). These values can also be obtained from Tables 15,18, and 20 in Appendix B.

 

Figure 30. Image. Spreadsheet Calculation of Bike I-S-I Values for Bicycle Example 3. The image is a screenshot showing the Excel spreadsheet calculation of the safety index values for the previous intersection. The appropriate data have been filled into the spreadsheet in order to calculate the Bicycle I-S-I values. In this example, the spreadsheet calculator produces a safety index Through value of 4.0, a safety index right-turn value of 2.3, and a safety index left-turn value of 3.4.

Figure 30. Spreadsheet calculation of bike ISI values for bicycle example 3.

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