An investigation of influential factors of downgrade truck crashes: A logistic regression approach

Truck crash occurrence causes extensive damage to lives and property. Truck crashes on downgrades exacerbate these costs due to the likelihood of a runaway being involved. Highway agencies have continuously sought engineering measures to reduce the incidence of such crashes. However, most past studies on truck crashes have focused on level roadway sections of highways without considering the effects of downgrades. The difference in geometric characteristics of downgrades and the mechanics of truck operations on such sections mean different factors may be at play in contrast to level roadway sections. This paper investigated the factors influencing truck crashes on downgrades; an attempt to fill in some of the research gaps. An empirical analysis of factors affecting truck crashes on two-lane downgrade roadways in Wyoming was carried out using a binary logistic regression technique. After calibrating the model, the effect of each significant variable was determined using theoretical concepts established in previous studies and engineering intuition. Crash factors including driver gender and age, weather, lighting and road conditions, number of crest curves, crash type, number of driveways, day of week and posted speed limit were found to be significant. The results of the study offer new understandings into how the identified factors influence truck crashes on downgrades.