WASHINGTON - Two out of every five drivers (41 percent) admit to having fallen asleep at the wheel at some point, with one in ten saying they've done so in the past year, according to a new AAA Foundation for Traffic Safety study. More than a quarter of those surveyed admitted they drove despite being so tired that they had difficulty keeping their eyes open in the previous month.

Eighty-five percent of drivers surveyed felt it was "completely unacceptable" for someone to drive if they are so tired they are having trouble keeping their eyes open. Unfortunately, drivers may not always be aware of the effects of fatigue resulting from a lack of sleep.

A new analysis of National Highway Traffic Safety Administration crash data estimates that about one in six (16.5 percent) deadly crashes, one in eight crashes resulting in occupant hospitalization and one in fourteen crashes in which a vehicle was towed involve a driver who is drowsy. These percentages are substantially higher than most previous estimates, suggesting that the contribution of drowsy driving to motor vehicle crashes, injuries, and deaths has not been fully appreciated.

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 100 miles.

• Traveling at times when you are normally awake, and staying overnight rather than driving straight through.

• Stop driving if you become sleepy.

Symptoms of sleepiness include but are not limited to:

• Having trouble keeping your eyes open and focused.

• The inability to keep your head up.

• Daydreaming or having wandering, disconnected thoughts.

• Drifting from your lane or off the road, or tailgating.

These findings were part of the AAA Foundation's third annual Traffic Safety Culture Index, a nationally-representative survey conducted by Abt SRBI Inc. The Traffic Safety Culture Index was a telephone survey of 2,000 U.S. residents ages 16 and older conducted from May 11, 2010 through June 7, 2010. The estimated proportion of crashes involving a drowsy driver is based on analysis of data from the National Highway Traffic Safety Administration's National Automotive Sampling System Crashworthiness Data System, a nationally-representative sample of crashes involving a passenger vehicle that was towed. Data analyzed was from years 1999-2008.

Additional information about the drowsy driving study, including the full report and fact sheet, is available at www.AAAFoundation.org.