Drivers are much more likely to die in a road traffic accident if they are obese, a new study has found.

And the more obese they are, the greater the risk.

US scientists assessed the details of over 57,000 road traffic accidents, which had been reported to the US Fatality Analysis Reporting System over a 12-year period. This system records all deaths that occur within 30 days of a road accident.

The team from the University of California focused on crashes that involved two vehicles and for which the impact of the crash led to the death of one or both drivers.

The scientists then focused on crashes where the drivers had been driving cars of similar type and size. They ended up with over 3,400 pairs of drivers to further assess. Of these, almost one in five was obese, one in three was overweight and the rest were a normal weight.

The study found that drivers were more likely to die in a road accident if they were obese and this risk increased the more obese they were.

The scientists used the World Health Organisation classification of obesity, i.e. levels one, two or three, with three being the heaviest.

The study showed that level one obese drivers were 21% more likely to die in a road traffic accident. At level two, this figure rose to 51% and at level three, it rose to 80%.

When the scientists analysed the data according to gender, they found that the risk was even greater for obese women. For example, level one obese drivers were 36% more likely to die in an accident.

While almost one in three of the people who died had not been using their seatbelt properly, the scientists said that overall, there was no major differences when it came to the use of seatbelts, nor were there differences when it came to the type of crash or type of car.

They said that one of the reasons obese people may have an increased risk is because they are more likely to have other health problems, which could increase their overall risk of death.

However, they also suggested that because of the growing obese population, car designs might have to change to accommodate bigger drivers.

"The ability of passenger vehicles to protect overweight or obese occupants may have increasingly important public health implications, given the continuing obesity epidemic. 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," they said.

Details of these findings are published in the journal, Emergency Medicine.