Seatbelt Effectiveness in Preventing Injury for Obese Drivers

Background: Seatbelt ineffectiveness has been hypothesized as a mechanism for the increased risk of injury for obese versus nonobese drivers. The purpose of this study is to understand seatbelt protection among obese drivers, and determine if the estimated benefits of seatbelts differ by body mass index (BMI). These results will illuminate important issues regarding the potential limitations of currently available safety technology as applied to an increasing segment of the U.S. population.

Methods: This case control study used data on adult drivers involved in frontal collisions between 1999 and 2008 from the National Automotive Sampling System-Crashworthiness Data System to determine if the effectiveness of seatbelts varied by BMI. Multivariate Poisson regression was used to determine the risk factors that influenced moderate to severe injury (maximum Abbreviated Injury Score, mAIS, 2 and greater (2+)), overall and by body region, by BMI.

Results: Of the 16,473 drivers analyzed, 21.7% (n=3,066) were obese. Obese drivers were significantly less likely than other drivers to be belted (p <0.001) and more likely to sustain mAIS2+ injury overall and to all body regions except the head, even when belted (p <0.001). As crash severity increased, obese drivers had the fastest rate of decline of seatbelt effectiveness, which for a severe crash was nearly 30% lower than for a nonobese driver. Similar findings, although of lesser magnitude were seen for overweight drivers.

Conclusions: These results suggest a need to ensure all drivers wear seatbelts and that seatbelts effectively mitigate injury-producing forces for drivers of all body sizes.