A Heterogeneity Based Case-Control Analysis of Motorcyclist Injury Crashes: Evidence from Motorcycle Crash Causation Study

Abstract: The main objective of this study is to quantify how different policy-sensitive factors are associated with risk of motorcycle injury crashes, while controlling for rider-specific, psycho-physiological, and other observed/unobserved factors. The analysis utilizes data from a matched case-control design collected through the FHWA Motorcycle Crash Causation Study. In particular, 351 cases (motorcyclists involved in injury crashes) are analyzed vis-a-vis similarly-at-risk 702 matched controls (motorcyclists not involved in crashes). The paper presents a novel heterogeneity based statistical analysis that accounts for the possibility of both within and between matched case-control variations. Overall, the correlations between key risk factors and injury crash propensity exhibit significant observed and unobserved heterogeneity. The results of best-fit random parameters logit model with heterogeneity-in-means show that riders with partial helmet coverage have a significantly lower risk of injury crash involvement. Lack of motorcycle rider conspicuity captured by dark (red) upper body clothing is associated with significantly higher injury crash risk (odds ratio 3.87). Importantly, a rider motorcycle-oriented lower clothing significantly lowers the odds of injury crash involvement. Formal motorcycle driving training in recent years was associated with lower injury crash propensity. Finally, riders with less sleep prior to crash/interview exhibited 1.97 times higher odds of crash involvement. Methodologically, the correlations of several rider, exposure, apparel, and riding history related factors with crash risk do not only vary in magnitude but in direction as well. The study results indicate the need to develop appropriate countermeasures, such as refresher motorcycle training courses, prevention of sleep-deprived/fatigued riding, and riding under the influence of alcohol/drugs.