- 5 The Highway Safety Manual Hsm Provides The Following Safety Performance Function Spf For Four Leg Signalized Int 1 (285.72 KiB) Viewed 38 times
5. The Highway Safety Manual (HSM) provides the following safety performance function (SPF) for four- leg signalized intersections that are located along rural two-lane highways: Nspf 4SG = exp[-5.13 + 0.60 × In (AADTmai) + 0.20 × In(AADT min)] where: Nspf 4SG=estimate of intersection-related predicted average crash frequency for base conditions for four-leg signalized intersections; ● AADT mai= AADT (vehicles per day) on the major road; and AADTmin= AADT (vehicles per day) on the minor road. The base conditions for such intersections assume there are no left-turn lanes nor right-turn lanes on any of the intersection approaches. Tables 10-13 and 10-14 from the HSM provide crash modification factors (CMFs) based upon the number of approaches on which there are auxiliary turn lanes. Table 10-13. Crash Modification Factors (CMF) for Installation of Left-Turn Lanes on Intersection Approaches. Number of Approaches with Left-Turn Lanesª Intersection Traffic Control One Approach Two Approaches Three Approaches Four Approaches Intersection Type Three-leg Intersection Minor road stop control 0.56 0.31 0.72 0.52 Four-leg Intersection Minor road stop control Traffic signal 0.82 0.67 0.55 0.45 *Stop-controlled approaches are not considered in determining the number of approaches with left-turn lanes Stop signs present on minor road approaches only. Table 10-14. Crash Modification Factors (CMF) for Right-Turn Lanes on Approaches to an Intersection on Rural Two-Lane, Two-Way Highways Number of Approaches with Right-Turn Lanes* One Approach Two Approaches Three Approaches Four Approaches Intersection Type Three-Leg Intersection Intersection Traffic Control Minor road stop control 0.86 0.74 0.86 0.74 Four-Leg Intersection Minor road stop control Traffic signal 0.96 0.92 0.88 0.85 *Stop-controlled approaches are not considered in determining the number of approaches with right-turn lanes. Stop signs present on minor road approaches only. Using this information, calculate the annual predicted number of crashes for an intersection that has the following characteristics: ● AADTmai = 15,000 veh/day ● AADTmin= 10,000 veh/day ● Left-turn lanes on all four approaches Right-turn lanes on two approaches (both on the major road) Using these data, estimate how many crashes would be expected at this intersection on an annual basis. (20 points)