People who are obese are more likely to die in car collisions than those of normal weight, U.S. researchers found.

For the study in Tuesday's issue of Emergency Medicine Journal, researchers used National Highway Traffic Safety Administration data on 6,806 drivers involved in traffic collisions, focusing on fatalities within 30 days of the crash.

Educating obese drivers about the importance of the proper use of the lap belt may lead to fewer fatal injuries. (Darryl Dyck/Canadian Press)

When Dr. Tom Rice of University of California at Berkeley and his co-authors analyzed the data by body mass index, they found obese drivers were more likely to die in severe collisions than normal weight drivers.

The least obese drivers were 21 per cent more likely to die than drivers of normal weight. The most obese with a BMI of 40 or higher were 78 per cent more likely to die.

It may be the case that passenger vehicles are well designed to protect normal weight vehicle occupants but are deficient in protecting overweight or obese occupants," the study's authors wrote, adding this could have public health implications given the obesity epidemic in the U.S.

"Efforts to educate obese drivers about the importance of the proper use of the lap belt may lead to reductions in severe and fatal injuries, particularly among women."

When the researchers looked for potential differences by sex, vehicle type, type of collision (such as head on versus side) and seat belt use, they said only sex showed a meaningful effect.

They found an increase in risk of death in underweight drivers who were male and the risk associated with being overweight was higher among women than men.

Almost a third of all drivers who had a fatal injury were not properly belted.

Heights and weights were not available for 23 per cent of the drivers. Of the drivers with complete information, 46 per cent had normal BMI, 33 per cent were overweight and 18 per cent were obese. The data came from motor vehicle state departments, which may not have been up to date or accurate.

Drivers in the study were matched to the other drivers involved in the collisions, which shared factors like time of day, ambulance response time and weather conditions to strengthen the analysis.

The researchers pointed to a previous study that suggested that the lower body of obese cadavers is propelled forward further on impact before the seatbelt engages the pelvis compared with those of normal weight.

Obese drivers may also be more likely to have underlying health problems, which the researchers called a "probable contributor." An earlier study of blunt trauma patients in intensive care found more chest injuries and fewer head injuries among obese patients.

Findings of smaller studies looking for associations between obesity and injury to body regions were either inconclusive, applied to only one type of collision or applied to only females in the case of pelvic fractures.