We all know it's dangerous to drink and drive, but many people do not realize that drowsiness can impair a driver's senses to nearly the same degree as a little alcohol. Drowsiness often causes a reduced awareness of surroundings and temporarily impairs vision. You may not notice that the car ahead has suddenly braked to a halt.

Even after you finally do sense the danger, drowsiness is likely to slow reaction time and keep the brain from quickly processing information that can help you prevent slamming into the rear bumper looming before you.

Who's at risk?

It is unknown exactly how many auto accidents are related to drowsiness. However, a 2005 poll by the National Sleep Foundation found that 60 percent of drivers admitted to driving drowsy in the past year, and 37 percent admitted to falling asleep at the wheel.

Certain people may be at increased risk of experiencing fatigue when driving. This includes people who work long hours, have untreated sleep disorders, and shift workers or commercial drivers. Statistics also show that young people, particularly males under age 26, are at higher risk for accidents related to drowsiness.

How do you know if you are too drowsy to drive? Typically, signs of fatigue grow steadily worse the longer you are behind the wheel. Your eyelids may droop and you may begin to nod off just before jerking back to attention. Constant yawning, disconnected thoughts and blurred vision are other signals of intense drowsiness when driving.