A new study from the Centers for Disease Control and Prevention reveals that at least 4.2 percent of American drivers have fallen asleep while driving. The CDC notes that "drowsy driving" may be responsible for 2.5 percent of all fatal car crashes, and the problem is more prevalent for drivers who sleep fewer than six hours each night.
The CDC used data from 141,076 people in 19 states who were asked, "During the past 30 days, have you ever nodded off or fallen asleep, even just for a brief moment, while driving?" The proportions of people admitting to drowsy driving ranged significantly based on age. Those aged 25 to 34 had the highest proportion, with 6.3 percent of drivers admitting to dozing at the wheel; drivers aged 35 to 44 followed at 5.5 percent, while drivers aged 65 or older were least likely to fall sleep in the car, with a reported rate of just 1.7 percent.
The CDC, however, says that one of the biggest predictors of whether people fall asleep while driving is how much sleep they get at night. Of respondents who slept six hours or fewer at night, 6.7 percent admitted to drowsy driving -- compared to 2.6 percent of drivers who slept seven to nine hours and 3.9 percent of those who slept ten or more hours.
One limitation of the study is that drivers were asked to self-report on whether they had nodded off behind the wheel, which the CDC says may lead to incorrect results because "persons often are not aware that they have fallen asleep" while driving. The agency also notes that it only collected data from drivers in 19 states -- those states already showed variations in reports of drowsy driving from 2.5 to 6.1 percent, so including all 50 states may provide more accurate results.
In November 2010, a survey by AAA found that 41 percent of drivers admitted to having fallen asleep behind the wheel. The survey also suggested that 16.5 percent of fatal crashes involved a drowsy driver.
The CDC says drivers who know they don't get enough sleep should be especially careful while driving. The agency says that tired drivers should pull over and rest; tricks like drinking coffee, turning up the radio volume, or using the air conditioning to make the cabin cooler proved ineffective in government tests.
Some automakers have launched in-car systems to monitor the driver and warn if he or she appears fatigued; the first widely available version was Attention Assist from Mercedes-Benz (pictured above).