Evaluating the benefits of using a context classification system to develop intersection safety performance functions

Abstract

Safety performance functions (SPFs) are used to predict intersection crashes. Unlike previous studies, which only used the three categories outlined in the Highway Safety Manual (HSM) to develop SPFs, this research developed SPFs based on a new context classification system developed by the Florida Department of Transportation (FDOT) which categorizes intersections into eight context categories. Two types of comparisons were used to evaluate the benefits of context-specific SPFs for the C3R-Suburban Residential and C4-Urban General context categories. First, individual intersection group SPFs were developed for unsignalized and signalized 3-leg and 4-leg intersection groups within each category. These individual SPFs were then compared to full category SPFs using data from all four intersection groups. The individual SPFs typically had lower performance measure values and more accurate crash predictions than the full SPFs while containing additional variables. For example, FDOT District 7 and major median were significant in several individual C3R SPFs but not in the full SPF. Next, comparisons were made between context-specific SPFs and HSM SPFs for two intersection groups (C3R signalized 4-leg and C4 unsignalized 3-leg). The context-specific SPFs outperformed the HSM SPFs in predicting multi-vehicle crashes, demonstrating the improved benefits that agencies can gain by developing context-specific SPFs.