Researchers from the University at Buffalo, in New York, analyzed U.S. National Highway Traffic Safety Administration data and found that normal-weight drivers were 67 percent more likely to wear a seat belt than morbidly obese drivers.

A person with a body-mass index (BMI) of 40 or higher is considered morbidly obese. A BMI between 18.5 and 24.9 is considered normal weight. BMI is a measure of body fat based on height and weight.

"We found that the relationship between the amount of obesity and seat-belt use was linear; the more obese the driver, the less likely that seat belts were used," study author Dr. Dietrich Jehle, a professor of emergency medicine and associate medical director at Erie County Medical Center in Buffalo, said in a university news release.

The study is scheduled to be presented May 10 at the annual meeting of the Society for Academic Emergency Medicine in Chicago.

Not using a seat belt increases the risk of serious injury and death in a crash, Jehle noted.

In a previous study, he and his colleagues found that morbidly obese people are 56 percent more likely to die in a motor vehicle crash than people of normal weight.