The National Highway Traffic Safety Administration tracks data on car accidents in the Fatality Analysis Reporting System (FARS). A recent analysis of fatal accidents between 1996 and 2008 showed a sharp increase in the risk of fatality for obese drivers involved in collisions with other vehicles. The study compared accidents where the vehicles involved were the same size and analyzed the fatality risk of drivers categorized by height and weight. Drivers with a body mass index (BMI) over 30, the accepted definition of "obese", were much more likely to die in their accidents than normal weight people.
The fatality risks were further broken down depending on the level of obesity of the person involved. Those with a BMI between 20 and 34.9 saw a 21 percent increase in the risk of death. A BMI between 35 and 39.9 saw a 51 percent increase in the risk of dying. Finally, those with a BMI higher than 40 saw an 81 percent increase in the likelihood of dying in a comparable accident.
The authors of this study cited a prior study indicating that obese people may move significantly farther forward, away from the vehicle seat, before seat belts hit the pelvis and halt the forward movement. They speculated that this additional movement could be contributing to the elevated fatality numbers. The lead author of the study pointed out that crash-test dummies may not be designed to account for the reality of American body types.
Source: New York Times, "An Unexpected Road Hazard: Obesity," by Nicholas Bakalar, 21 January 2013