Research shows fat people are propelled further forward because of their additional soft tissue which prevents a seat belt from tightening immediately against the pelvis.
Scientists now believe car design may have to change to protect overweight drivers.
Analysis of US collision data found those who were most overweight -- in the World Health Organisation obesity category III -- were 80pc more likely to die in an accident than drivers of a healthy weight.
Those in category II were 51pc more likely to be killed in a crash, while the risk was 21pc for those in category I.
When broken down by gender, obese women were found to be at greater risk than men. Those in obesity category III were almost twice as likely to die on the road than their male counterparts, the scientists said.
Their analysis of more than 3,403 pairs of drivers also showed underweight men were more likely to die in a collision.
The authors, from the University of California and the University of West Virginia, 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.
"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."