Motorcycle Crash Causation Study
Motorcyclists are vulnerable road users at a particularly high risk of serious injury or death when involved in a crash. When controlled for exposure (as per mile traveled in 2015), the number of motorcycle fatalities is nearly 29 times the number of passenger vehicle fatalities. Owing to the expanding concern, the U.S. Congress recently passed a legislation to initiate the most comprehensive research effort targeted at identifying the causes of motorcycle crashes. While extensive work has been done with regards to rider safety, much of the literature is based on traditional police crash reports and/or behavioral questionnaires.
Our recent and ongoing work related to rider safety departs from the main body of literature by harnessing comprehensive data from a matched case-control design collected through the FHWA’s Motorcycle Crash Causation Study.
In particular, 351 cases (motorcyclists involved in injury crashes) are analyzed vis-à-vis similarly-at-risk 702 matched controls (motorcyclists not involved in crashes). Unlike traditional conditional estimation of relative risks, the study presented 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 (U.S. DOT compliant helmets with partial coverage, least intrusive covering only the top half of the cranium) 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, 95% CI: 1.63, 9.61).
Conducting a deeper analysis of the injury crashes only, we examine how different “policy-sensitive” factors correlate with anatomical injury severity (injury severity score – ISS), while controlling for rider and crash specific factors as well as other observed/unobserved factors. With a focus on head injury mechanisms and rider conspicuity, we found that motorcycle-specific shoes and retroreflective upper body clothing correlate with lower ISS on-average by 5.94 and 1.88 units respectively. Riders with only partial helmet coverage on-average sustained more severe injuries, whereas, riders with acceptable helmet fit had lower ISS.
Likewise, almost no evidence exists in literature regarding the discrimination power of better anatomical injury measures in differentiating clinical outcomes in motorcycle crashes. Furthermore, multiple injuries to different body parts of a rider are seldom analyzed. Anatomy, physiology, and rider host factors interact in complex ways complicating the injury evaluation of riders. To get a full picture of the actual harm sustained by the riders, we harness detailed information about rider host profiles and anatomical, physiological indicators – that collectively capture the effects of demographics (age, gender) and co-morbidities complications (multiple injuries sustained by riders) across a diverse spatiotemporal pattern of motorcycle crashes. This information is seldom available in traditional crash datasets available for analysis. With regards to injury evaluation, we examined the utility of anatomically referenced injury measures (as opposed to police-reported KABCO scale) in predicting post-crash trauma and mortality outcomes.
Publications:
Wali, Behram, Asad J. Khattak, and Numan Ahmad. “Examining correlations between motorcyclist’s conspicuity, apparel related factors and injury severity score: Evidence from new motorcycle crash causation study.” Accident Analysis & Prevention 131 (2019): 45-62. PDF
Wali, Behram, Asad J. Khattak, and Aemal J. Khattak. “A heterogeneity based case-control analysis of motorcyclist’s injury crashes: Evidence from motorcycle crash causation study.” Accident Analysis & Prevention 119 (2018): 202-214. PDF
Wali, B., Ahmad, N., & Khattak, A. J. (2021). Toward better measurement of traffic injuries–Comparison of anatomical injury measures in predicting the clinical outcomes in motorcycle crashes. Journal of Safety Research. PDF
Major Contributors:
Asad J. Khattak, Ph.D., Beaman Distinguished Professor, University of Tennessee, Knoxville.
Numan Ahmad, M.S., Graduate Research & Teaching Assistant, University of Tennessee, Knoxville.
Aemal J. Khattak, Ph.D., Professor, University of Nebraska, Lincoln.
This paper is based on work supported by the US Department of Transportation through the Collaborative Sciences Center for Road Safety (CSCRS), a consortium led by The University of North Carolina at Chapel Hill (UNC) in partnership with The University of Tennessee. The data for this study were provided by the Federal Highway Administration (FHWA). The assistance of Ms. Carol Tan (Team Leader, Safety Data and Analysis Team, FHWA) and Mr. Yusuf Mohamedshah (SHRP 2 Safety Data Analyst, FHWA) is highly appreciated.