BOSTON (TheStreet) -- You know that driving while intoxicated can cost you your license or even your life, but did you know that "driving while drowsy" plays a role in one-sixth of all fatal car accidents?

"People know that drunk driving is dangerous and [socially] unacceptable, but drowsy driving is a much more gray area. Drivers tend to underestimate its danger and overestimate their ability to deal with it," says Bruce Hamilton of the AAA Foundation for Traffic Safety, which recently polled more than 2,300 Americans about the issue.

Some 28.3% of respondents admitted to driving drowsy at least once in the 30 days before taking the survey, including 19% who reported doing so more than a single time. Two percent even conceded to getting behind the wheel "fairly often" or "regularly" while drowsy during the month before taking the survey.

Hamilton says that's bad given that AAA researchers estimate drowsy driving plays a role in 16.5% of fatal car crashes, 13.1% of auto accidents that involve hospitalizations and 7% of incidents where vehicles require towing.

He says studies have found that worn-out drivers sometimes unknowingly take "micro-sleeps," involuntary naps that last just a few seconds but long enough for accidents to occur.

"I think people don't fully appreciate the effect that drowsiness can have on their driving," Hamilton says. "They believe that they can still drive safely, but our research shows that they can't."

In fact, the expert says drowsy driving is so dangerous that vehicle operators need to recognize its symptoms and pull over -- fast.

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"If you get to the point where you're so drowsy that you can't safely drive, you should treat that as an emergency situation," Hamilton says.

Signs he says drivers need to look for include:

  • repeated yawning or difficulty keeping your head up;
  • rubbing your eyes and/or finding it hard to keep your eyes open and focused on the road;
  • erratic driving behavior, such as swerving, tailgating, drifting out of your lane, hitting rumble strips, missing traffic signs or missing an exit you planned to take;
  • feeling irritable or restless;
  • struggling to remember the last few miles driven.

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Hamilton says consumers can minimize the risk of drowsy driving by:

  • getting a least seven hours of sleep the night before a long trip;
  • scheduling long drives for hours when you're normally awake anyway;
  • pulling over and taking a break after every two hours or 100 miles of driving;
  • having coffee or other caffeinated products and not driving for at least 30 minutes until the anti-fatigue effects kick in;
  • avoiding heavy meals or medications that can make you sleepy;
  • traveling with a passenger who'll take turns behind the wheel and remain alert while you drive;
  • staying somewhere overnight if necessary.

The expert says he understands that in today's hectic world, job requirements or family commitments often make driving while drowsy seem unavoidable.

But Hamilton says Americans need to recognize the dangers they face if they get behind the wheel while fatigued.

"No matter how important a business meeting or other event seems," he says, "the reality is that if you fall asleep at the wheel, you might never get there."