Injury risks and crashworthiness benefits for females and males: Which differences are physiological?

Brumbelow, Matthew L. / Jermakian, Jessica S.
Insurance Institute for Highway Safety
February 2021

Objective: Previous research has found elevated injury risk for females relative to males in passenger vehicle crashes but has not accounted for ways the crashes themselves differ between these populations. Vehicle curb weight, ride height, safety rating, airbag deployment, and crash configuration all influence injury outcome and often are not well-represented by delta-V alone. This study evaluated the effect of occupant sex on injury risk in front and side crashes while limiting or controlling for non-physiological crash differences. Additionally, the effects of crashworthiness improvements were compared for females and males.
Methods: We analyzed National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) cases from 1998–2015 involving a belted driver in a front crash or a front-row near-side occupant in a side crash. Logistic regression was used to estimate the risk of certain injury outcomes for females relative to males as well as the change in risk due to improved crashworthiness. Sex-based differences in occupant age, mass, and stature; crash test rating; delta-V; crash configuration; and vehicle-to-vehicle compatibility were considered either through case selection or the inclusion of additional regression covariates.
Results: Before controlling for crash and vehicle differences, female drivers in front crashes had higher estimated overall and body-region-specific risks of a Maximum Abbreviated Injury Scale (MAIS) >= 2 injury and a MAIS >= 3 injury, as consistent with previous findings. After accounting for such differences, all female injury odds ratios were reduced. Females remained at higher risk of MAIS >= 2 injury (odds ratio [OR], 2.23; 95% confidence interval [CI], 1.42–3.51), especially extremity injury, but had similar odds for MAIS >= 3 non-extremity injury (OR, 0.98; 95% CI, 0.56–1.7). While controlling for crash differences in side impacts, female injury odds tended to be lower than male injury odds for MAIS >= 2 and higher for MAIS >= 3 outcomes, but none of the estimates were significant at the p = 0.05 level. Estimated benefits of improved crashworthiness were similar or greater for females than for males for most injury outcomes.
Conclusions: Female-specific crashworthiness improvements may be required to provide additional protection against Abbreviated Injury Scale (AIS) 2 extremity injury. Much of the remaining discrepancy in sex-based injury risk can be attributed differences between vehicles and crashes, not to physiological differences. Addressing these differences will require other types of countermeasures.