Xuesong Wang,Kun Xie,Mohamed Abdel-Aty,Paul J.Tremont,Xiaohong Chen
Abstract:Safety Performance Functions (SPFs) are typically used to correlate geometric, traffic and environmental characteristics with total crashes and to identify hotspots that have excessive overall crash frequencies. However, different crash types are associated with different vehicle maneuvers and therefore different risk factors. This study developed approach-level SPFs using a full Bayesian method to assess the safety effects of specific risk factors for rear-end, left-turn, right-angle, and sideswipe crash types, and for total crashes. To account for the spatial correlations among approaches at the same intersection, a random intersection-specific effect term was incorporated into each model. It was concluded that these models can be used to identify specific safety problems associated with high risk intersections, and can serve as useful complements to general hotspot analyses using expected crash totals. In addition, it was found that certain variables (e.g. number of through lanes, median, and left-turn protection all on the entering approach) could have even contrary effects on crash occurrence of different types. Approach-level crash type models provide valuable insights in developing countermeasures aimed at reducing certain crash types and an improved ability in identifying deficiencies related to geometric and traffic characteristics for each intersection approach.