A Study on Crash Risk and Its Influencing Factors on Expressways

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A growing concept on crashes is that crashes are associated with the interaction of "inadequate" geometric design, "disruptive" traffic flow and "adverse" ambient conditions. However, existing models prevailingly developed based on individual factors, and the rationalities of these factors are missing. Therefore, the study analyzed the mechanisms of these factors affecting crashes, and finally developed a crash risk estimation model (CREM) considering the interaction of these factors at expressway basic segments. CREM was developed separately for urban and intercity expressways and further compared based on expressway type to more accurately understand the causes of crashes. CREM was then tested regarding the evolving process of crash risk following traffic density and the safety quality of geometric design. The results reveal that CREM can provide leverage to predict hazardous conditions and avoid an impending crash. Meantime, it can be applied to assess safety benefit of geometric design, which supplies a benchmark for evaluation of performance-check geometric design. Crash-prone locations are identified to be traffic condition-dependent and it is more applicable for operation.