Expected Crash Estimation

Previous research on the number of crashes that have occurred in roadway corridors, at intersections, and at other crossings with certain characteristics can be used to estimate the number of pedestrian or bicycle crashes that may be expected in a particular location on or near campus. An advantage of applying this type of approach is that it can be used to estimate the decrease in pedestrian or bicycle crashes that may occur at a location if a particular safety treatment is applied.

One tool for estimating the expected change in crashes at a location due to a particular pedestrian or bicycle safety treatment is a crash modification factor (CMF). For example, installing a median island on an arterial roadway at an uncontrolled marked crosswalk location is expected to reduce pedestrian crashes by 46% (crash modification factor of 0.54) (Zegeer et al. 2005). Pedestrian and bicycle CMFs are available from the FHWA Crash Modification Factor Clearinghouse. A more sophisticated method to estimate expected crashes at a particular location is to apply a safety performance function (SPF). Safety performance functions typically express the relationship between several variables, such as traffic volumes and a number of roadway characteristics on expected crashes. For example, signalized intersections are expected to have more pedestrian crashes when they have higher motor vehicle volumes, higher pedestrian volumes, and more lanes to cross (Harwood et al. 2008). SPFs are discussed in the AASHTO Highway Safety Manual.

Considerations: There are still relatively few pedestrian and bicycle crash modification factors and safety performance functions. In addition, the specific context that applied in the study to derive a particular crash modification factor may not apply to a campus context (e.g., the study may have only used data from state highway intersections, most of which have higher traffic volumes than residential neighborhood intersections near a campus). Therefore, it may not be possible to find an appropriate crash modification factor or safety performance function to estimate expected pedestrian or bicycle crashes for all locations of interest near a campus.

Applications: CMFs were one of the tools used to quantify the suitability of walking along and across roadways on and around the University of California, Berkeley campus (Schneider, et al. 2012). For example, since a FHWA CMF Clearinghouse study suggested that permitting right-turn-on-red at signalized intersections was associated with 43% more pedestrian crashes, intersections around the campus where right-turn-on-red was permitted were assigned 43 more points. Points were assigned similarly for other features (positive points for more expected crashes and negative points for fewer expected crashes).

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