The researchers found that belted male drivers with a Body Mass Index (BMI) of 35-50 have a 22 percent lower probability of being killed in a crash than belted underweight drivers (BMI between 15 and 18.4). However, for unbelted males, it is the opposite. The probability of death from a crash is 10 percent higher for obese men, compared to the underweight men.
For women, a normal BMI (18.5-24.9) leads to a lower rate of death. Both overweight and underweight women have a higher risk, 10 percent and 8 percent, respectively. There was no difference in rate between belted or unbelted women drivers.
The researchers looked at data from 300,000 drivers in fatal crashes from the National Highway Traffic Safety Administration (NHTSA) over a 10-year period (1998-2008). In these crashes, 51 percent were killed, but drivers who did not belt up were more than twice as likely to die in a crash. NHTSA's data shows that when seat belts are used properly, they can reduce the risk of fatal injury by 45 percent.
The researchers note that these findings underscore the need to evaluate seat belts, seats, and air-bag designs to see if there needs to be improvement to adequately protect men and women at higher and lower BMI ranges. There was a change in 2007 to the frontal air bags and that does take into account weight and size, but not necessarily for above- or below-average people.
They further concludes that changes may also need to be made to the crash test procedures and use of various dummies to adequately represent all shapes and sizes of American drivers.—Liza Barth