Most people are well-aware of the danger posed by drunk drivers, but tired drivers may be an even more dangerous problem on the road today, as a tired driver's response times and accuracy may be even more impaired than someone who has had a few drinks.

Researchers studied 39 subjects from the transportation industry and the army

They measured response times and accuracy of subjects after being sleep deprived for up to 28 hours and also after consuming alcohol up to a blood alcohol concentration (BAC) of 0.1%, which is the limit in most states to be considered "intoxicated".

After 17-19 hours without sleep, performance on some tests was equivalent or worse than that at a BAC of 0.05%, which is the limit in most states for being considered "ability impaired".

According to the authors:

Response speeds were up to 50% slower for some tests and accuracy measures were significantly poorer than at this level of alcohol. After longer periods without sleep, performance reached levels equivalent to the maximum alcohol dose given to subjects (BAC of 0.1%) ... .  

To go seventeen hours without sleep may sound like a lot until you consider that if you wake up at 6 AM you will be up 17 hours by 11 PM. Taking into account that many people often go out late at night to movies, bars, dancing, etc., they could easily be up well over 19 hours, not to mention the fact that they may have had a few alcoholic drinks as well. Add to this the fact that many medications, even non-prescription ones, can cause drowsiness (see Driving While Medicated).

"These findings reinforce the evidence that the fatigue of sleep deprivation is an important factor likely to compromise performance of speed and accuracy of the kind needed for safety on the road and in other industrial settings," the authors conclude.