A Planning-Level Methodology for Identifying High-Crash Sections of Virginia’s Primary System

About the report:

The Virginia Department of Transportation (VDOT) has been developing safety performance functions (SPFs) as a way to identify sites with a potential for safety improvement more effectively.  An SPF estimates the expected safety performance of a roadway as a function of its characteristics.  Using SPFs, VDOT can identify which roads have a significantly higher number of crashes than would be expected based on site conditions.  Other VDOT studies have developed SPFs with a microscopic perspective that separately examine individual intersections or discrete roadway segments. 

The purpose of this study was to develop an SPF-based methodology to conduct more intermediate-scale safety analyses.  VDOT’s Traffic Engineering Division indicated that such a methodology would be useful for corridor screening and planning-level applications.  The scope of the study was limited to the following roadway types in Virginia’s primary system: rural two-lane, rural multilane divided, rural multilane undivided, urban two-lane, urban multilane divided, and urban multilane undivided.  For each type, roadway inventory data, traffic volume data, and crash data from 2003 through 2007 were compiled and integrated into a database. 

This study then took an approach that diverged from that of other SPF research to develop intermediate-scale SPFs.  Instead of crashes at intersections and on roadway segments being separated, intersection and segment crashes were combined and mapped onto the appropriate roadway inventory links.  In addition, site aggregation was performed to combine similar, adjacent roadway links into longer aggregated sites.  SPFs were then generated from these aggregated sites through regression analysis.  A site prioritization demonstration was then performed using the aggregate SPFs and aggregate sites to create lists of sites with the highest potential for safety improvement.  Finally, a comparison of these lists and those generated by the critical rate method produced quantitative evidence of the advantage of the developed SPF-based methodology over the traditionally used critical rate method.  Once implemented, the methodology developed in this study should enable VDOT to conduct corridor screening and planning-level analyses in a more effective and cost-efficient manner.    

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