Analysis of injury severity in low-speed electric vehicle crashes: Insights from partially temporally constrained modeling and out-of-sample prediction.

OBJECTIVE: Low-speed electric vehicles (LSEVs), as an important component of global micromobility systems, are increasingly prevalent in mixed traffic environments in developing countries. However, existing studies have paid limited attention to crash causation heterogeneity and temporal instability under open-road conditions. This study aims to investigate the temporal instability and unobserved heterogeneity of crashes involving three-wheeled and four-wheeled low-speed electric vehicles in China. METHODS: Crash data from Shandong Province, China, covering the period from 2021 to 2023, were analyzed. Likelihood ratio tests were conducted to examine temporal instability and vehicle-type heterogeneity. Based on the test results, partially temporally constrained random parameter logit models with heterogeneity in both the mean and variance were developed separately for different vehicle types. In addition, out-of-sample prediction was employed to compare the safety performance of three-wheeled and four-wheeled low-speed electric vehicles. RESULTS: Significant temporal instability and vehicle-type heterogeneity were identified in the crash data. The estimation results showed that, contrary to findings from conventional motor vehicle studies, male drivers were associated with a lower likelihood of severe injury in crashes involving low-speed electric vehicles. Older drivers were consistently identified as a high-risk group across both vehicle types. Furthermore, out-of-sample prediction results indicated that four-wheeled low-speed electric vehicles exhibited consistently lower crash severity risk than three-wheeled low-speed electric vehicles, and this safety advantage increased from 2021 to 2023. CONCLUSIONS: This study reveals significant temporal instability and unobserved heterogeneity in crashes involving low-speed electric vehicles. The findings provide important insights into the safety differences between three-wheeled and four-wheeled low-speed electric vehicles and offer valuable implications for traffic safety management, vehicle regulation, and policy development related to LSEVs.