Assessing motorcyclist injury severity on curved road segments with temporal dynamics and unobserved heterogeneity.

Motorcyclists face an increased risk of injury severity at curved roadway segments due to a wide range of factors. Given the complex and evolving nature of factors influencing motorcyclist injury severity on curved roadway segments, there is a need for research that not only captures these contributing factors dynamics but also considers temporal variations and unobserved heterogeneity. The study used mixed logit models to analyze 8815 motorcycle crashes that occurred on curved segments in Texas between 2017 and 2022. Several normally distributed random parameters were identified, including clear weather, fixed objects, a 40-60 mph speed limit, White ethnicity, and riders aged 25-54 years old. Average marginal effects indicated increased fatal injury likelihood during cloudy weather, on marked lanes, roads without median, and collisions with fixed objects. Consistent factors affecting fatal injury severity across yearly models included cloudy weather and fixed-object collisions (increasing), daylight (decreasing), and riders aged 15-24 (decreasing). Interestingly, darkness in 2020 showed reduced fatal injury likelihood, likely due to lower traffic volumes and increased rider caution during the COVID-19 pandemic, contributing to less severe crash outcomes. These findings emphasize the need to consider temporal variations to understand changing risk factors and dynamics in motorcycle injury severity on curved road segments.