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Drowsy driving can cause drivers to be less responsive to driving events in a way that potentially increases the risk of crashing (Lyznicki et al., 1998). In one study, participants with sleep deprivation were worse at lane keeping than participants with no sleep deprivation. The effect was greater in the morning even on short drives (Caponecchia & Williamson, 2018). The AAAFTS aimed to quantify the relationship between sleep deprivation and crash risk (Tefft, 2016). A sample of 4,571 crashes that occurred from July 2005 to December 2007 in the United States was analyzed using a case-control design. Elevated crash risk was associated with fewer number of hours of sleep in the 24 hours before a crash. Drivers who reported less than 4 hours, 4 to 5 hours, 5 to 6 hours, and 6 to 7 hours of sleep were associated with a 11.5, 4.3, 1.9, and 1.3 times increase in crash rate, respectively, than drivers who reported sleeping at least 7 hours of sleep in the past 24 hours. In addition, the study also estimated that changes from normal sleep patterns can elevate drivers’ crash risk. Overall, drivers who averaged 4 to 5 hours of sleep daily were estimated to have 5.4 times the crash rate of drivers who averaged 7 or more hours of sleep (Tefft, 2016).

NHTSA surveyed 4,010 drivers in 2002 and found 11% reported that they had nodded off while driving during the past year (Royal, 2003). Of those who nodded off, 66% said they had 6 or fewer hours of sleep the previous night. A 2020 study found that nearly all drivers (95%) believe it is unacceptable to drive while excessively drowsy, yet 17.3% admitted to having driven while too tired to easily keep their eyes open in the past 30 days (AAAFTS, 2021).

A CDC analysis of the Behavioral Risk Factor Surveillance System phone survey across 19 States and the District of Columbia found that about 4% of 147,076 respondents reported falling asleep while driving at least once in the past 30 days (Wheaton et al., 2013). This proportion was consistent with a different sample of over 90,000 U.S. residents surveyed in 2011 and 2012 (Wheaton et al., 2014). A meta-analysis of 17 international studies published from 1993 to 2014 reported that drivers who self-reported experiencing sleepiness while driving were at more than twice the risk of being involved in a motor vehicle crash compared to drivers who reported no such instances (Bioulac et al., 2017).

Age, gender, and other risk factors play a role in driving while drowsy. Studies have found that young drivers and male drivers were more likely than older drivers and female drivers to have dozed off at the wheel (Tefft, 2010; Royal, 2003; Wheaton et al., 2013; Wheaton et al., 2014). Drowsy driving was also found to be more prevalent among binge drinkers and those that seldom or never used seat belts while in a car (Wheaton et al., 2014), which suggests that drowsy driving may be more prevalent among drivers who engage in other risky behaviors.

Drowsy driving does not just occur late at night; about one-quarter of those drivers who admit to nodding off say the most recent incident occurred in the afternoon (noon to 5 p.m.) (Royal, 2003). Additionally, drowsy driving is not limited to long trips—roughly half of the drivers who nodded off had been driving for an hour or less. A driving simulator study conducted in Australia identified another vulnerable group of fatigue-prone drivers—regular commuters (Caponecchia & Williamson, 2018).

Driver drowsiness is a critical issue for commercial drivers. About 14% of truck drivers reported a near-crash due to drowsiness according to a 2012 survey by the National Sleep Foundation (NSF, 2012). FMCSA, in partnership with Transport Canada and several Canadian Provinces, created the North American Fatigue Management Program (NAFMP) to research and educate against fatigued driving (FMCSA, 2016). FMCSA regulates drowsiness in commercial drivers through hours of service regulations, driver logs, and inspections; starting December 2017 the use of electronic logging devices (ELDs) was made mandatory for commercial bus and truck drivers (FMCSA, 2015). NHTSA has also developed a prototype drowsy driver warning system that appears promising in reducing drowsiness among drivers of heavy vehicles (Blanco et al., 2009; Brown et al., 2014).

Drowsy driving may result from lifestyles that include insufficient or irregular sleep (shift workers, for instance) or from medical conditions beyond a driver’s immediate control. For example, a recent CDC study in 29 States found that people in certain occupational groups—production, healthcare support, healthcare practice, food preparation, protective services, and some transportation services—were more at risk for having short sleep duration of less than 7 hours each day (Shockey & Wheaton, 2017). Moreover, studies indicate that drivers themselves are poor judges of the performance decrements that result from drowsiness (Powell & Chau, 2011). A change in the social perception of sleep and public awareness about the risks of drowsy driving are necessary to change a driver’s decisions to drive when drowsy (Higgins et al., 2017).

In 2015 NHTSA hosted a forum bringing together the traffic safety and sleep science communities called Asleep at the Wheel: A Nation of Drowsy Drivers (Higgins et al., 2017). The objective was to address drowsy driving through an interdisciplinary approach. As a result of the Forum, NHTSA released the Drowsy Driving Research and Program Plan in 2016 and, later, Asleep at the Wheel: A National Compendium of Efforts to Eliminate Drowsy Driving (NHTSA, 2017). Together, the publications describe projects quantifying the drowsy driving problem. Additionally, they also examine various efforts to build public awareness and education, develop policy; explore efforts at identifying high-risk populations, and look at advancing vehicle technology and infrastructure as countermeasures (Higgins et al., 2017; NHTSA, 2016; NHTSA, 2017).

Other Federal agencies are also concerned about the drowsy driving problem. The NTSB reported that about 36 major transportation investigations from 2001 to 2012 identified fatigue as a potential cause or contributing factor; this included approximately 14 highway incident investigations (Fischer, 2016; Marcus & Rosekind, 2017). The NTSB added “human fatigue” as an issue in its Most Wanted List of Transportation Safety Improvements in 2016 (Fischer, 2016).

Behavioral strategies for drowsy driving focus on removing some of the underlying causes or promoting awareness of the risks. Drowsy driving that is related to a driver’s job may be reduced through employer policies and programs. Drowsy driving caused by medical conditions, such as obstructive sleep apnea, or by drugs or medications may be addressed through policies, communications, and outreach. Similarly, communications and outreach may be useful in raising awareness of specific drowsiness issues among certain high-risk populations. However, few studies have examined whether the standard behavioral countermeasures of laws, enforcement, and sanctions (which are used successfully for alcohol impairment, seat belt use, aggressive driving, and speeding) are effective for drowsy drivers.

There are a variety of environmental and vehicular strategies to address drowsy driving. Rumble strips, both on the shoulder and the centerline, have demonstrated their effectiveness in preventing crashes associated with inattention or drowsiness (Persaud et al., 2016). Other roadway improvements, such as wide and visible edge lines, more easily visible road signs, and better lighting at night can help drivers who are not fully alert, particularly due to sleepiness. These strategies are not discussed further in this chapter because they do not fall under the purview of SHSOs.