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. This study examined data from a representative sample of crashes that occurred in the United States between 3 July 2005 and 31 December 2007, involved at least one light vehicle that was towed due to damage, resulted in an emergency medical services dispatch, and were subject to on-scene multidisciplinary investigations as a part of a special study by the U.S. Department of Transportation. Investigations included assessment of drivers’ recent sleep. This study quantifies the relationship between the number of hours that a driver had slept in the past 24 hours and the risk of crash involvement using a case-control study design. Cases were drivers who on-scene crash investigators found to have committed an unsafe or illegal action, inaction, or error that they determined was the critical reason for the critical event that led to the crash; controls were drivers not found to have contributed to the crash in such a way. Logistic regression was used to adjust for potential confounding by driver age, time of day, crash location, and recent changes in sleep schedule. Controls were assumed to have been sampled from among all drivers on the road in proportion to their exposure, thus the odds ratio associated with a particular amount of sleep approximates the ratio of the exposure-based crash involvement rates associated with that amount of sleep compared with a reference amount. The final sample comprised 7,234 drivers involved in 4,571 crashes. Drivers who had slept for less than 4 hours, 4-5 hours, 5-6 hours, and 6-7 hours in the past 24 hours had an estimated 11.5, 4.3, 1.9, and 1.3 times the crash rate, respectively, of drivers who had slept for 7 hours or more in the past 24 hours. In an alternative analysis of drivers’ usual daily hours of sleep and sleep in the past 24 hours relative to their own usual amount of sleep, drivers who reported that they usually slept for 4-5 hours daily had 5.4 times the crash rate of drivers who reported that they usually slept for 7 hours or more; drivers who reported that in the past 24 hours they had slept for 1-2 hours less than usual, 2-3 hours less than usual, 3-4 less than usual, and 4 or more hours less than usual had 1.3, 3.0, 2.1, and 10.2 times the crash rate, respectively, of drivers who reported that they had slept for at least their usual amount. This study may underestimate the risk of driving while sleep-deprived, because data on crashes that occurred between midnight and 6 AM were not available, and other studies have shown that the effects of sleep deprivation on attention and performance are greatest during the early morning hours. Experts recommend that healthy adults should sleep for at least 7 hours daily. 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., and the increase in crash rate associated with driving after less than 4 hours of sleep is much greater. (Author/publisher)
Samenvatting