Yatin J. Patel, MD Medical Director, Center for Sleep Studies, Goshen General Hospital, Goshen, IN 46526 Phone 574.534.9911 Fax 574.534.6915
	Home

Summary of Several Scientific Studies on this serious subject;

SLEEPINESS IMPAIRS PERFORMANCE

Sleepiness leads to crashes because it impairs elements of human performance that are critical to safe driving (Dinges, Kribbs, 1991).

Slower reaction time.
Sleepiness reduces optimum reaction times, and moderately sleepy people can have a performance- impairing increase in reaction time that will hinder stopping in time to avoid a collision (Dinges, 1995). Even small decrements in reaction time can have a profound effect on crash risk, particularly at high speeds.

· Reduced vigilance.
Performance on attention- based tasks declines with sleepiness, including increased periods of nonresponding or delayed responding (Haraldsson et al., 1990; Kribbs, Dinges, 1994) (see figure 2).

· Deficits in information processing.
Processing and integrating information takes longer, the accuracy of short-term memory decreases, and performance declines (Dinges, 1995). Fall-asleep crashes are likely to be serious.

The morbidity and mortality associated with drowsy-driving crashes are high, perhaps because of the higher speeds involved (Horne, Reyner, 1995b) combined with delayed reaction time.

In North Carolina, more of these crashes resulted in injury compared with other, nonalcohol-related crashes-fatalities occurred in 1.4 percent and 0.5 percent, respectively (Pack et al., 1995).

Pack (1995) and Maycock (1996) both conclude that a higher proportion of the most serious crashes are sleepiness related. A single vehicle leaves the roadway. An analysis of police crash reports in North Carolina showed the majority of the nonalcohol, drowsy-driving crashes were single-vehicle roadway departures (Pack et al., 1995).

Among New York State drivers surveyed about their lifetime experience with drowsy driving, almost one-half of those who had a fall-asleep or drowsy-driving crash reported a single-vehicle roadway departure; about one-fourth of those who had fallen asleep without crashing also reported going off the road (McCartt et al., 1996).

NHTSA General Estimates System data reflect the same trend but also suggest that sleepiness may play a role in rear-end crashes and head-on crashes (Knipling, Wang, 1994). The crash occurs on a high-speed road.

In comparison with other types of crashes, drowsy-driving crashes more often take place on highways and major roadways with speed limits of 55 to 65 mph (Knipling, Wang, 1994; Wang, Knipling, Goodman, 1996).

Pack and colleagues (1995) found that most sleepiness-related crashes occur at higher speeds, attributing this finding to the effect of sleep loss on reaction time. NHTSA figures show that most drowsiness- or fatigue-related crashes occur on higher speed roads in nonurban areas. However, Maycock (1996) found that a greater absolute number occur in built-up areas.

Panel members noted the possibility that more crashes occur on high-speed roads because more long-distance nighttime driving occurs on highways. The driver does not attempt to avoid crashing. NHTSA data show that sleepy drivers are less likely than alert drivers to take corrective action before a crash (Wang, Knipling, Goodman, 1996).

Anecdotal reports also suggest that evidence of a corrective maneuver, such as skid marks or brake lights, is usually absent in fall-asleep crashes. The driver is alone in the vehicle. In the New York State survey of lifetime incidents, 82 percent of drowsy-driving crashes involved a single occupant (McCartt et al., 1996). Conversely, respondents who reported having fallen asleep without crashing were less likely to have been alone in the automobile.