Night shift workers are more likely to crash their cars than people who work during the day, a study into fatigue-related accidents has found.

Researchers at the University of North Carolina at Chapel Hill found that drivers who did not work nights were four or five times less likely to crash their vehicle.

The project's principle investigator, Dr Jane Stutts, said that the researchers believed the study was the first of its kind to contact large numbers of drivers involved in sleep-related crashes soon after their accident.

The research - funded by the American Automobile Association Foundation for Traffic Safety - found that people involved in "sleep" mishaps had a very different profile from drivers involved in other accidents.

Other factors strongly associated with "drowsy crashes" included - not surprisingly - sleeping less than six hours a night, being awake for 20 hours or longer, and frequent driving between midnight and 6am.

Working 60 or more hours a week also increased drivers' risk - 27% of drivers in fatigue-related car crashes worked 60 or more hours weekly.

Drivers in sleep-related crashes were also twice as likely to have more than one job, the survey found.

Dr Stutts said: "My impression when I talked to a lot of these people was, 'well no wonder you fell asleep at the wheel, you must have been exhausted'.

"We found that drivers in sleep and fatigue-related crashes were four to five times more likely than drivers in the control crash group to work night shift jobs.

"Everyone who doesn't get enough sleep on a regular basis, however, is at risk. The vast majority of people in our study who crashed as a result of driving while drowsy either got too little sleep on a routine basis and built up what sleep researchers describe as "sleep debt", or they got far too little sleep before trying to drive."

The Automobile Association says that fatigue is a factor in 10-20% of accidents in the UK.

The AA's head of road safety, Andrew Howard, said that drivers should never attempt to drive more than two hours without taking a break of at least 20 minutes, and should never drive more than eight hours in one day.

Business drivers and elderly affected

He said: "At this time of year, the people involved in fatigue-related accidents are different to at the rest of the year.

"At any other time, the people who are most affected are business drivers, who will drive four hours to a meeting, have the meeting and then drive four hours back.

"They are under a lot of pressure, are quite blasé about driving, and would rather not "waste" the 20 mins stopping to take a break.

"At this time of the year, however, the people affected tend to be those who aren't used to driving long distances, but are visiting friends and family over Christmas and the New Year. They tend to be older people."