Heavier people are up to 80 per cent more likely to die in an accident than drivers of a healthy weight, but the risk doubles for obese women, according to research published in the Emergency Medicine Journal.
The study found that obese people are propelled further forward during a collision because their additional soft tissue prevents the seat belt tightening immediately against the bones of the pelvis, the 'Daily Mail' reported.
The study included 6,806 drivers involved in 3,403 collisions, of which 18 per cent were classified as obese, 33 per cent were overweight and 46 per cent had a healthy weight. Obesity is defined as having a Body Mass Index (BMI) of 30 or above.
The findings showed those who were most obese, with a BMI of 40 and above, were 80 per cent more likely to die in an accident than drivers of a healthy weight.
Those who were severely obese (with a BMI of 35-39.9) were 51 per cent more likely to be killed in a crash, while the excess risk was 21 per cent for obese people with a BMI of 30-34.9.
Obese women were found to be at greater risk than men, with a BMI of 35 and over roughly doubling the risk of death compared with women of normal weight.
The biggest risk for men was a 75 per cent higher risk of death among the most obese, while underweight male drivers were also more likely to die in a collision than those of a healthy weight.
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Two thirds of those studied were men, and almost one in three was aged between 16 and 24; one in three was not using a seat belt properly - lap or shoulder only, rather than both - and in half of cases, the airbag deployed.
Dr Tom Rice, Division of Environmental Sciences, Safe Transportation and Research Center, University of California at Berkeley, California, said the obesity epidemic meant car design should come under the microscope.
"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," he said.
"Findings from this study suggest that obese vehicle drivers are more likely to die from traffic collision-related injuries than non-obese occupants involved in the same collision," he added.
"Obese cadavers had significantly more forward movement away from the vehicle seat before the seat belt engaged the pelvis owing to additional soft tissue that prevents the belt from fitting close to the pelvis when the cadavers were in the driving position," the study said.
"The additional forward motion by cadavers was seen for the abdomen and lower extremities," it said.