Sleep deprived drivers more likely to have car crashes

Insufficient sleep can dramatically increase a driver's risk of being involved in car crashes, a study has found.

The study, published in the journal SLEEP, showed that those who have slept for less than seven of the past 24 hours have higher odds of being in an accident.

The risk is greatest for drivers who have slept fewer than four hours, researchers said.

While the dangers of driving drowsy were already well known, the study is the first to quantify the relationship between how much a driver has slept and his or her risk of being responsible for a crash.

Researchers from AAA Foundation for Traffic Safety, a US-based non profit, analysed data from in-depth investigations of a sample of 5,470 crashes, including interviews with the drivers involved.

They found that drivers who reported fewer than four hours of sleep had 15.1 times the odds of responsibility for car crashes, compared with drivers who slept for the recommended seven to nine hours in the preceding 24-hour period.

This is comparable to the crash risk of a driver with a blood alcohol concentration roughly 1.5 times the legal limit.

Researchers involved in the study also discovered that drivers who reported six, five, and four hours of sleep in the past 24 hours had 1.3, 1.9 and 2.9 times the odds of responsibility for a crash, respectively, compared with a driver who slept for seven to nine hours.

Drivers who reported less than four hours of sleep had particularly elevated risk of single-vehicle crashes, which are more likely to result in injury or death.

Drivers who had changed their sleep or work schedule in the past week and drivers who had been driving for 3 hours or longer without a break were also found to be at increased risk.

"Being awake isn't the same as being alert. Falling asleep isn't the only risk," said Brian Tefft, from AAA Foundation for Traffic Safety.

"Even if they manage to stay awake, sleep-deprived drivers are still at increased risk of making mistakes -- like failing to notice something important, or misjudging a gap in traffic -- which can have tragic consequences," Tefft said.