V. POPULATION GROUPS AT HIGHEST RISK All drivers who experience the chronic or acute situations described in section IV are at risk for drowsy driving and drowsy-driving crashes. Although no one is immune from risk, research to date clearly identifies three broad population groups at high risk for drowsy-driving crashes. Their higher risk is based on (1) evidence from crash data of a greater absolute or relative number of fall-asleep crashes and/or (2) increased intermediate risk, based on subjective reports of their having higher levels of sleepiness and more of the chronic or acute factors that underlie risk for everyone. The three groups at high risk are young people, shift workers, and people with untreated sleep conditions. YOUNG PEOPLE, ESPECIALLY YOUNG MEN Virtually all studies that analyzed data by gender and age group found that young people, and males in particular, were the most likely to be involved in fall-asleep crashes (Pack et al., 1995; Horne, Reyner, 1995b; Maycock, 1996; Knipling, Wang, 1994). Definitions of "young" differed among authors; the ages included in this category fell between 16 and 29. Young people. Knipling and Wang (1995) found that drivers younger than 30 accounted for almost two-thirds of drowsy-driving crashes, despite representing only about one-fourth of licensed drivers. These drivers were four times more likely to have such a crash than were drivers ages 30 years or older. In Pack and colleagues' study (1995), 20 was the peak age of occurrence of drowsy-driving crashes, whereas in New York State the greatest number of drowsy drivers (on self-report) were within the 25-to-34 age group (McCartt et al., 1996), and both the 18-to-24 and 25-to-39 age groups were overrepresented in fall-asleep crashes (New York State Task Force, 1996). Horne and Reyner (1995a) suggest that a combination of having more of the chronic and acute risk factors and frequently being on the roads during nighttime hours (greater exposure) may explain the greater incidence of drowsiness-related crashes in youth. Carskadon (1990) offers a variety of age-specific reasons for the involvement of younger people, particularly adolescents. During this period, young people are learning to drive, experimenting and taking risks, and testing limits. At the same time, this age group is at risk for excessive sleepiness because of the following: Maturational changes that increase the need for sleep. Changes in sleep patterns that reduce nighttime sleep or lead to circadian disruptions. Cultural and lifestyle factors leading to insufficient sleep, especially a combination of schoolwork demands and part-time jobs, extracurricular activities, and late-night socializing. In one study (Carskadon, 1990), boys with the greatest extracurricular time commitments were most likely to report falling asleep at the wheel. The subgroup at greatest risk comprised the brightest, most energetic, hardest working teens. The panel felt that vulnerability may be further increased when young people use alcohol or other drugs because sleepy youth are likely to be unaware of the interaction of sleepiness and alcohol and may not recognize related impairments they experience. Males. In North Carolina, males were found to be at the wheel in about three of four fall-asleep crashes (Pack et al., 1995). NHTSA data show that males are 5 times more likely than females to be involved in drowsy-driving crashes (Wang, Knipling, Goodman, 1996). The reasons young males have more crashes than do young females are not clear because both young men and young women are likely to be chronically sleep-deprived. SHIFT WORKERS Most shift workers have at least occasional sleep disturbances, and approximately one-third complain of fatigue (Åkerstedt, 1995a, 1995b, 1995c). Older shift workers appear to have more sleep-related difficulties than do younger workers, but no gender differences have been found (Harma, 1993). Night shift workers typically get 1.5 fewer hours of sleep per 24 hours as compared with day workers. The midnight to 8 a.m. shift carries the greatest risk of sleep disruption because it requires workers to contradict circadian patterns in order to sleep during the day (Kessler, 1992). Investigations have demonstrated that circadian phase disruptions caused by rotating shift work are associated with lapses of attention, increased reaction time, and decreased performance (Dinges et al., 1987; Hamilton et al., 1972; Williams et al., 1959). A study of hospital nurses reached similar conclusions based on "real world" experiences. Rotating shifts (working four or more day or evening shifts and four night shifts or more within a month) caused the most severe sleep disruptions of any work schedule. Nurses on rotating schedules reported more "accidents" (including auto crashes, on-the-job errors, and on-the-job personal injuries due to sleepiness) and more near-miss crashes than did nurses on other schedules (Gold et al., 1992). About 95 percent of night nurses working 12-hour shifts reported having had an automobile accident or near-miss accident while driving home from night work (Novak, Auvil-Novak, 1996). Hospital interns and residents routinely lose sleep during on-call periods, which may last 24 hours or more. A survey of house staff at a large urban medical school found that respondents averaged 3 hours of sleep during 33-hour on-call shifts, much of which was fragmented by frequent interruptions (Marcus, Loughlin, 1996). About 25% reported that they had been involved in a motor vehicle crash, 40% of which occurred while driving home from work after an on-call night. Others reported frequently falling asleep at the wheel without crashing, for example, while stopped at a traffic light. Although this evidence does not demonstrate a conclusive association between shift work and crashes, the panel believes that shift workers' increased risks for sleepiness are likely to translate into an increased risk for automobile crashes. Competing demands from family, second jobs, and recreation often further restrict the hours available for sleep and further disrupt the sleep schedule. The panel also designated shift workers as a high-risk group because the number of people who perform shift work-and are thus exposed to crash risk-is increasing. This sector is growing at a rate of 3% per year, as businesses such as overnight deliveries, round-the-clock computer operations, overnight cleaning crews, 24-hour markets, and continuous-operation factories prosper and expand. Currently about one in five men (20.2%) and almost one in six women (15%) work other than a daytime shift, including evening, night, rotating, split, and irregular shifts (Kessler, 1992). PEOPLE WITH UNTREATED SLEEP APNEA SYNDROME AND NARCOLEPSY Although the absolute number of crashes is low, crash risk is increased among people with untreated sleep apnea syndrome (SAS) and narcolepsy. The proportion of crashes is higher for people with untreated narcolepsy than it is for people with untreated SAS. However, because SAS is more common than narcolepsy, the absolute number of crashes is higher for those with untreated SAS (Aldrich, 1989). In addition, patients with untreated SAS or narcolepsy perform less well on driving simulation and vigilance or attention tests than do people without these disorders (Findley, 1995; American Thoracic Society, 1994; Haraldsson et al., 1990). Undiagnosed sleep-disordered breathing, ranging from habitual snoring to repeated breathing interruptions, also increases the likelihood of crashes in a dose-response manner (Stradling et al., 1991; Philip et al., 1996; Hanning, Welch, 1996; Ohayon, Priest, Caulet, et al., 1997). Although these conditions place people at higher risk for drowsy-driving crashes, they are not invariably linked with impaired driving. For example, many people with these disorders report no auto crashes (Findley et al., 1988; Aldrich, 1989). Findley and colleagues (1989) found that patients with severe untreated sleep apnea had more frequent crashes than did those with untreated mild apnea. A patient who can recognize impending uncontrollable sleepiness and take precautions is less likely to be at risk than one who is unaware of or denies his or her sleepiness (Aldrich, 1989). Sleep apnea syndrome is somewhat more common among males than among females, and typical patients tend to be overweight and middle aged or older, with a large collar size and history of loud snoring; however, women and men without this profile also have the disorder (American Thoracic Society, 1994). People with narcolepsy are as likely to be female as male, and the disorder usually begins in adolescence. The time from onset of symptoms to diagnosis of narcolepsy averages 10 years (American Thoracic Society, 1994; National Commission on Sleep Disorders Research, 1993). Currently, many people with these conditions are undiagnosed and untreated, unaware of the potentially serious consequences of driving while drowsy, or unaware of the seriousness of the difficulty they may experience in maintaining alertness (Arbus et al., 1991; Hansotia, 1997). Falling asleep at the wheel may be a major factor that motivates undiagnosed patients to seek medical care. The matter is rarely raised in driver or law enforcement education, and even health care professionals may not recognize a history of sleepiness as a risk factor for fall-asleep crashes. Medical systems have been successful in identifying only a fraction of the population with symptomatic sleep apnea (Strohl, Redline, 1996). VI. COUNTERMEASURES The panel reviewed the knowledge base in four categories of countermeasures: behavioral, medical, alerting devices, and shift work. They found only a few scientific evaluations of potential countermeasures, most of which were laboratory studies. Reports that exist tend to address the biological feasibility of reducing drowsiness or improving alertness, rather than demonstrate an intervention that reduces drowsy-driving crashes. As noted earlier, more research is needed on this topic. Countermeasures for drowsy driving aim either to prevent it or to ameliorate it after it occurs. The panel concluded that preventing drowsiness with adequate sleep before driving is both easier and much more successful than any remedial measure reviewed. Methods of obtaining adequate sustained sleep include creating a positive sleep environment (a room that is cool, quiet, and dark) and sleeping at regularly scheduled times. Such measures are often promoted as "sleep hygiene" and make intuitive sense; however, few rigorous studies support all sleep hygiene claims. The panel noted that the wake-up effects from remedial approaches to existing sleepiness do not last long. At best they can help sleepy drivers stay awake and alert long enough to find a motel, call for a ride, or stop driving and sleep. They are not a substitute for good sleep habits and should not be viewed as a "driving strategy" that can get drowsy drivers safely to their destination. BEHAVIORAL INTERVENTIONS In addition to getting adequate sleep before driving, drivers can plan ahead to reduce the risk of drowsy driving in other ways. Some evidence exists that napping before a long drive may help make up for sleep loss in the short term and enhance wakefulness during the drive. Napping has the greatest effect on performance several hours after the nap (Dinges et al., 1987; Dinges, 1992, 1995). Two other proven interventions avoid known problem situations: not drinking alcohol when sleepy (Roehrs et al., 1994) and not driving between midnight and 6 a.m. (Mitler et al., 1988; Åkerstedt, 1995c), especially well into the period when sleep is usual (Brown, 1994). Graduated driver-licensing programs that disallow late-night driving among younger drivers can mandate this risk-avoiding behavior (Waller, 1989; Frith, Perkins, 1992). When a driver becomes drowsy, the most obvious behavioral step for avoiding a crash is to stop driving and sleep for an extended period. When this approach is not practical and another driver is not available to take over, studies have found two remedial actions that can make a short-term difference: Napping. Taking a break for a short nap (about 15 to 20 minutes) has been shown to improve subsequent performance, even among sleep-deprived people (Horne, Reyner, 1995a; Dinges et al., 1987; Philip et al., 1997). Naitoh (1992) found that short naps every 6 hours during a 35-hour (otherwise sleepless) period was effective in maintaining performance in the laboratory. However, nappers are often groggy for about 15 minutes upon awakening from naps longer than 20 minutes (Dinges, 1992). Practical issues with this strategy include the inability of some people to take short naps and the need for secure rest areas. The New York State survey found that about one-third of drivers had needed or wanted to stop in the past year, but a rest area was not available. Many also were unlikely to use a rest area when they were driving alone at night. Consuming caffeine. Caffeine, even in low doses, significantly improves alertness in sleepy people (but only marginally in those already alert) (Regina et al., 1974; Lumley et al., 1987; Griffiths et al., 1990; Lorist et al., 1994). The minimum dose needed can be obtained in about two cups of percolated coffee, although caffeine content of coffee varies widely (Fox, 1993). Caffeine also is available in other forms such as caffeine-fortified soft drinks and tablets. In driving simulators, sleep-deprived drivers who consumed caffeine reduced lane deviations, potential crashes, and sleepiness for about an hour after consumption (Horne, Reyner, 1995a). In addition, limited evidence suggests that physical discomfort (such as sitting in an uncomfortable seat or position and shivering or sweating) may also keep sleepy drivers awake (Åkerstedt, Ficca, 1997). Nicotine can improve short-term performance significantly in people with cognitive or attention performance impairments such as those from sleepiness (Kerr et al., 1991). Obviously, however, smoking tobacco should not be generally recommended in an educational campaign as a drowsy-driving countermeasure because the well-established risks substantially outweigh the possible benefits. The panel found no evidence of effectiveness for commonly accepted remedial approaches such as brief exercise (e.g., getting out of the car and walking around for a few minutes) (Horne, 1988), listening to the car radio, or opening the car windows (Horne, Reyner, 1995a). The panel found no studies evaluating other driver-reported steps such as talking to another passenger, talking on a cellular phone or CB radio, chewing gum or ice, or snacking. One study suggests that talking on a cellular phone while driving is associated with increased crash risk (Redelmeier, Tibshirani, 1997). MEDICAL INTERVENTIONS TO TREAT NARCOLEPSY AND SLEEP APNEA SYNDROME Although effective treatments are available for both narcolepsy and obstructive sleep apnea, relief of sleepiness and related symptoms is not always easily achievable for all patients (Broughton et al., 1981; Haraldsson et al., 1995). Although treatment can improve driving simulator performance (Findley et al., 1989), individual performance varies. A few studies to date have evaluated crash experiences of patients successfully treated for these disorders and found a positive effect (Cassel et al., 1996; Haraldsson et al., 1995). An impediment to diagnosis is a lack of physician education on the recognition of sleepiness and sleep disorders (National Commission on Sleep Disorders Research, 1993). ALERTING DEVICES To date, research has validated only one type of device that alarms or awakens drivers who are drowsy or asleep-shoulder rumble strips placed on high-speed, controlled-access, rural roads. A recent synthesis of reports on the effectiveness of rumble strips shows that they reduce drive-off-the-road crashes by 30 to 50 percent-the only countermeasure the panel found in any category that has a demonstrated effect on crashes. Rumble strips also appear to be a relatively low-cost solution with a positive benefit-to-cost ratio (Garder, Alexander, 1995; National Sleep Foundation, June 1997). However, the effectiveness of rumble strips has been demonstrated only in drive-off-the-highway crashes; their value with other types of sleepiness or inattention crashes or other types of roads has not been studied. Section II lists some of the technological in-vehicle monitors designed to detect and evaluate driver sleepiness. Some of these devices contain alarms or other alerting devices that go off when indications of sleepiness occur. Controlled trials are needed to evaluate the usefulness of these tools. An inherent deficiency in all types of alerting devices is that many people continue to drive even when they know they are drowsy and fighting to stay awake. Although an effective alerting device may prevent one crash, a driver who falls asleep once is likely to fall asleep again unless he or she stops driving. Some safety experts have expressed concern that alerting devices may in fact give drivers a false sense of security, encourage them to drive long after impairment, and inhibit their taking effective behavioral measures to prevent or relieve sleepiness (Lisper et al., 1986; Dinges, 1995; Horne, Reyner, 1995a). SHIFT WORK MEASURES Research has shown that effective steps are available for both employers and employees to reduce the likelihood of excessive sleepiness and drowsy driving. Because of the complexity of the issues involved (Rosekind et al., 1995), a combination of alertness management approaches is likely to be most effective. Researchers also have found differences in individual tolerance to shift work (Harma, 1993); knowing more about the biological and behavioral factors that determine these differences could provide direction for future educational efforts. EMPLOYER MANAGEMENT OF WORK SCHEDULES Several approaches have been effective in reducing sleepiness caused by working irregular hours and nighttime hours. To minimize disruption and help employees adjust to circadian rhythm changes, employers should educate employees about the problem (Harma, 1993). In addition, periods of work longer than 8 hours have been shown to impair task performance and increase crashes. For example, performance appears worse with a 12-hour, 4-day week schedule than with an 8-hour, 6-day week (Brown, 1994). In jobs with extended hours, the scheduling of work and rest periods to conform to circadian rhythms promotes better sleep and performance (Stampi, 1994). Another effective approach is to allow and facilitate napping for night shift workers (Dinges, 1992; Naitoh, 1992). EMPLOYEE BEHAVIORAL STEPS Shift workers themselves can take steps to reduce their risks of drowsy driving by planning time and creating an environment for uninterrupted, restorative sleep (good sleep hygiene) (Minors, Waterhouse, 1981; Rosa, 1990). Shift workers who completed a 4-month physical training program reported sleeping longer and feeling less fatigue than did matched controls who did not participate in the program. However, individual response to the stresses of shift work varies (Harma, 1993), and the background factors or coping strategies that enable some workers to adapt successfully to this situation are not well defined. The behavioral steps discussed earlier for younger males also seem reasonable for reducing risk in this population. Nurses working the night shift reported using white noise, telephone answering machines, and light-darkening shades to improve the quality and quantity of daytime sleep (Novak, Auvil-Novak, 1996). USING BRIGHT LIGHT TREATMENTS Several studies show that timed exposure to bright light has been successful in helping shift workers and those suffering from jet lag adapt to and overcome circadian phase disruption (Czeisler et al., 1990; Stampi, 1994). This approach promotes longer, uninterrupted sleep, which may help reduce sleepiness on the job and behind the wheel. The panel did not find data linking such treatment to changes in rates of crashes or industrial accidents.