that people cannot reliably detect how sleepy they are, and when they are likely to fall asleep, presumably because they either lack or do not pay attention to signs that sleep onset is likely. (FHWA, 1998; Filliatrault et al, 1996; Itoi et al, 1993)
People frequently deny how sleepy they are, and whether their sleepiness interferes with their driving. In one study, a man who had a crash and reported sleeping only 5 hours a day claimed that because he did not remember what happened, he must have “blacked out” rather than fallen asleep. Another driver from a sleep-related crash said “I wasn’t drowsy, I just fell asleep.” This study found that only about half of drivers in sleep-related crashes reported feeling drowsy before their crashes, with nearly one-quarter reporting that they felt “not at all drowsy.”(Stutts, 1999) However, several telltale factors strongly suggest a sleep-related accident, including a vehicle leaving the roadway, and a lack of braking, skid marks, or other evidence that the driver made no attempt to avoid crashing. Police investigators often take that evidence into consideration when classifying an accident as sleep-related.(NHLBI, 1998a)
Research has revealed a few indicators of drowsiness and drowsy driving. (Papadelis et al, 2007; Mathis and Hess, 2009)These include:
Currently, there is no definitive physiologic test or detection system for drowsiness equivalent to the breath analyzers used to detect drunk driving.
Individual prevention of drowsy driving crashes
Experts agree that there is no substitute for sleep, and drivers should ensure they are well rested to prevent crashes. (Nguyen et al, 1998) Awareness of the signs of drowsiness might be helpful, but only if drivers attend to those signs by pulling off the road and getting sufficient sleep. If that is not possible, studies suggest two interventions that are helpful: taking a short, 20-minute nap, and/or drinking two cups of coffee or other equivalently caffeinated beverages. Caffeine will improve alertness only for a short