Effects of heavy rainfall in different light conditions on crash severity during Arizona's monsoon season

Environmental factors, including adverse weather and light conditions, have been widely recognized as contributing factors to crash severity and frequency. Heavy downpours occur during the monsoon season in Arizona and surrounding areas during the summer. Considering the effects of light conditions on driver perception of adverse weather, and thus on crash risk, this study investigates the effects of weather and light conditions on crash severity by estimating four separate multinomial logit models for specific weather (heavy rainfall or clear) and light conditions (daytime or nighttime). Marked differences were found between these conditions in terms of the significant factors affecting crash severity. Drivers likely behave differently in different environmental conditions. Findings indicated that addressing factors such as age groups, speed limits, roadway types, slow driving in heavy rain, and excessive speeding with safety strategies and educational efforts may improve traffic safety during heavy rainfall as well as in clear weather. Various other significant factors are discussed and compared based on the weather and light conditions models.