  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.
