Previous research by the AAA Foundation for Traffic Safety has estimated as many as 7% of all crashes, 13% of crashes that result in hospital admission, and 21% of fatal crashes involve driver drowsiness. However, the relationship between specific measures of sleep deprivation and crash risk has not been quantified in the general driving population. The results of this study indicate that drivers who usually sleep for less than 5 hours daily, drivers who have slept for less than 7 hours in the past 24 hours, and drivers who have slept for 1 or more hours less than their usual amount of sleep in the past 24 hours have significantly elevated crash rates. The estimated rate ratio for crash involvement associated with driving after only 4-5 hours of sleep compared with 7 hours or more is similar to the U.S. government’s estimates of the risk associated with driving with a blood alcohol concentration equal to or slightly above the legal limit for alcohol in the U.S.