Temporal stability of factors affecting injury severity in rear-end and non-rear-end crashes: A random parameter approach with heterogeneity in means and variances

Rear-end crashes have become a serious global issue, with increasing injuries and fatalities accounting for massive property loss. The purpose of this study is to investigate the variation in the influence of factors affecting injury severity in rear-end and non-rear-end crashes and the change in impact degree over time. Using the three-year crash data of the Beijing–Shanghai Expressway from 2017 to 2019, the heterogeneity and temporal stability of contributing factors affecting rear-end and non-rear-end crashes were investigated through a group of random parameter logit models with unobserved heterogeneity in means and variances. Then, the temporal stability and transferability of the models were evaluated using likelihood ratio tests. Moreover, the marginal effects were calculated to explore the temporal stability and potential heterogeneity of the contributing variables from year to year. Using four possible injury severity outcomes, namely, fatal injury, severe injury, minor injury, and no injury, a wide variety of possible factors significantly affecting injury severity outcomes including environmental, temporal, spatial, traffic, speed, geometric, and sight distance characteristics were analyzed. Considerable differences were observed in the rear-end and non-rear-end crashes, and the contributing factors indicated statistically significant temporal instability in both crashes over the three-year period. This study can be of value in promoting highway safety aimed at rear-end and non-rear-end crashes and developing suitable safety countermeasures.