Two out of every five drivers say they've fallen asleep behind the wheel at some point, a troubling new study has found.

One in 10 drivers admitted to falling asleep or nodding off while driving in the past year, while more than a quarter of drivers acknowledged being so sleepy while driving in the last month, they've had trouble keeping their eyes open.

The research comes from a survey of 2,000 American drivers and was conducted for the AAA (American Automobile Association) Foundation for Traffic Safety, a non-profit research and educational group.

The survey revealed that men (52 per cent) were more likely than women (30 per cent) to report having ever fallen asleep while driving.

As well, more than half (59 per cent) of those drivers who reported having fallen asleep while driving in the past year said they had been driving for less than an hour before falling asleep; only one in five reported they had been driving for three hours or longer.

The study is being released in support of Drowsy Driving Prevention Week, a week-long campaign to remind all drivers about the dangers of driving while tired.

AAA Foundation President and CEO Peter Kissinger says he believes the dangers of driving while tired are underestimated by most drivers. He worries that too many drivers take an attitude of 'I'm tired, but I can make it," but endanger the lives of others while doing so.

"We need to change the culture so that not only will drivers recognize the dangers of driving while drowsy but will stop doing it," he said in a statement.

Kissinger notes that being drowsy while driving decreases awareness, slows reaction time, and impairs judgment in much the same way that drugs or alcohol do.

The study includes a new analysis of crash data from the U.S. National Highway Traffic Safety Administration and estimates that about one in six fatal crashes -- about 17 per cent -- and one in eight crashes resulting in hospitalization involve a driver who is drowsy.

These percentages are substantially higher than most previous estimates; according to NHTSA's 2008 Traffic Safety Facts publication, only 2.4 per cent of fatal crashes involve a drowsy driver. But AAA Foundation says their re-analysis suggests the problem is worse then those estimates.

The analysis also found that younger drivers aged 16 to 24 were nearly twice as likely to be involved in a drowsy driving crash as drivers aged 40-59.

To remain alert and avoid drowsiness, AAA suggests:

  • Getting plenty of sleep (at least six hours) the night before a long trip
  • Scheduling a break every two hours or every 160 kilometres
  • Drink a caffeinated beverage if needed. But since it takes about 30 minutes for caffeine to enter the bloodstream, find a safe place to take a 20-30 minute nap while waiting for the caffeine to take effect
  • Traveling at times when you are normally awake, and staying overnight rather than driving straight through the night
  • Stop driving if you become sleepy; someone who is tired could fall asleep at any time.