Exploring the inter-relationship among hazardous actions, causal factors, and motorcyclist injury severity using path analysis

Hazardous actions are the critical contributor to motorcyclist injury severity, which are typically treated in parallel with other causal factors in crash severity models. However, hazardous actions may result directly from the interaction between road users, roadway, and environmental factors. So, causal factors may indirectly influence motorcyclist injury severity through hazardous actions. The research attempts to investigate the direct, indirect, and total effects of causal factors on motorcyclist injury severity, emphasizing the role of hazardous actions as mediators. A path analysis approach is employed to model the complex relationship among hazardous actions, other causal factors, and motorcyclist injury severity. Specifically, two models are developed within the path analysis framework, namely, a random parameters logit model to examine the relationship between contributing factors and hazardous actions, and a correlated random parameters logit model with heterogeneity in means to assess the correlation between these factors and motorcyclist injury severity. Using motorcycle crash data in Michigan from 2015 to 2018, the study finds that factors such as stop/yield signs, intersections, one-way traffic, two-lane roads, midnight/early morning, weekends, and dawn/dusk do not directly affect motorcyclist injury severity but significantly influence hazardous actions, thereby indirectly increasing injury severity through these actions. Moreover, alcohol or drug use, speed limits of 55 mph or higher, and motorcycle age of six years or older significantly increase the risk of hazardous actions and motorcyclist injury severity, thus exacerbating injury severity through the indirect influence of hazardous actions. Additionally, divided median strips with or without traffic barriers, rain/snow weather, and darkness with streetlights directly reduce injury severity but indirectly increase it via hazardous actions. These findings underscore the complex inter-relationship among hazardous actions, other causal factors, and motorcyclist injury severity, offering valuable insights for enhancing motorcycle safety by addressing hazardous actions as a central factor.