Injury severity of drowsy drivers involved in single vehicle crashes: Accounting for temporal instability and unobserved heterogeneity

Abstract

Drowsy driving has received comparatively less attention in traffic safety literature when compared to other safety issues, despite its devastating impact on society in terms of human life lost and associated economic burdens. Therefore, this significant safety threat requires a thorough investigation. To address the temporal instability of factors contributing to crashes involving drowsy drivers, this paper divides the crash data into four time periods while capturing unobserved heterogeneity in the means and variances of random parameters. To explore the determinants affecting the severity of injuries sustained by drowsy drivers involved in single-vehicle crashes, injury outcomes are categorized into three groups: serious, moderate, and no injuries. Using four years of crash data from the state of Washington between 2013 and 2016, a wide range of factors were examined, including driver characteristics, roadway conditions, crash characteristics, vehicle conditions, lighting conditions, and temporal factors. The estimation results reveal that there is temporal instability in terms of the effect of determinants on injury severity across the years. However, some factors exhibit stable effects, such as female drivers, sober drivers, and non-hit-and-run crashes. Based on the findings of this study, decision-makers, traffic engineers, and traffic authorities can gain valuable knowledge and insights into the factors contributing to drowsy-related crashes, enabling them to make informed recommendations for safety countermeasures.