An analysis of factors influencing driver action on downgrade crashes using the mixed logit analysis

Abstract

Crash rates from national and state sources conclusively show that vehicles of all types are prone to crashes on Wyoming downgrades. Crashes on steep downgrades are exacerbated by difficult terrain and an increase in the driving task required to safely navigate such landscape. An important step to evaluate safety on downgrades is to analyze the effects of driver action due to its influence on vehicle operation and crash outcomes. This analysis is critical due to the difference in vehicle dynamics on downgrades compared to level sections. However, most studies on driver action have been disparate and not focused on downgrades. This has led do a dearth of literature on the subject. This paper developed mixed (random parameter) logit models to evaluate factors impacting driver action on downgrades for single- and multiple-vehicle crashes. The approach accounts for unobserved heterogeneity potentially related to crash characteristics, driver factors, and road surface condition. The results were mostly consistent with previous studies, but some unexpected results were highlighted and explained in the light of published literature and engineering intuition.