Drowsy and Distracted Drivers

Section I


The American Association of State Highway and Transportation Officials' (AASHTO's) Strategic Highway Safety Plan identified 22 goals to pursue in order to significantly reduce highway crash fatalities. One of the plan's hallmarks is to comprehensively approach safety problems through a series of guides. The range of strategies available in the guides will ultimately cover various aspects of the road user, the highway, the vehicle, the environment, and the management system. The guides strongly encourage the user to develop a program to tackle a particular emphasis area from each perspective in a coordinated manner.

AASHTO's overall goal is to move away from independent activities of engineers, law enforcement, educators, judges, and other highway safety specialists and to move toward coordinated efforts. The implementation process outlined in the series of guides promotes forming working groups and alliances that represent all of the elements of the safety system. In so doing, they can use their combined expertise to reach the bottom-line goal of targeted reduction of crashes and fatalities associated with a particular emphasis area.

Goal 6 in the Strategic Highway Safety Plan is keeping drivers alert. For the purposes of this guide, the focus is on inattentive driving due to driver distraction or fatigue. The identified objectives and strategies are aimed at both decreasing the occurrence of distracted or fatigued driving and making the consequences of lapses of attention less severe.

General Description of the Problem

The National Highway Traffic Safety Administration (NHTSA) has identified driver inattention as a causative factor in 2530 percent of crashes. Inattentive drivers may be temporarily distracted by something inside or outside the vehicle, may be drowsy or fatigued, or may simply have their mind on something other than the task of driving.

The primary source of national data on the role of driver inattention in traffic crashes is the Crashworthiness Data System (CDS), which is based on a national sample of police-reported traffic crashes involving at least one passenger vehicle that has been towed from the crash scene. An analysis of 20002003 CDS crash data shows that

  • 11.6 percent of crashes involve one or more distracted drivers,
  • 3.9 percent involve one or more drivers who were sleepy or had fallen asleep at the wheel, and
  • 10.2 percent involve one or more drivers who "looked but didn't see."

Overall, the percentage of crashes with one or more drivers identified as inattentive (i.e., distracted, fatigued, or "looking but not seeing") was 25.5 percent. The actual percentage is likely higher, since information on driver attention status was unknown or missing for many of the crash-involved vehicles.

Exhibit I-1 uses an "iceberg" analogy to illustrate the difficulties of documenting the true extent of the drowsy and distracted driver crash problems and to illustrate the relationship between drowsiness and distraction. Crash investigations are retrospective reconstructions of crashes based primarily on crash scenarios, driver and witness statements, and physical evidence at the scene. Police and other investigators are reluctant to allege driver factors such as drowsiness and distraction without explicit statements from drivers or witnesses or a crash scenario that clearly indicates these factors. Just "below the surface" are many undocumented cases where drivers know that they were drowsy or distracted, but don't admit this to police. Furthermore, at a deeper level, drivers themselves may not be aware of the effects of these factors on their driving. In addition, sleep deprivation can itself lead to loss of vigilance, so that much driver inattention may have its roots in drowsiness caused by sleep deprivation and natural time-of-day variations in alertness.


"Iceberg" Analogy of Drowsy and Distracted Driver Crash Problems

Fatigue has also been identified as a problem for commercial vehicle operators, especially long-haul truck drivers. This is primarily due to the more frequent nighttime driving, extended driving times, and irregular sleep schedules that characterize long-haul trucking operations. An estimated 1 percent of all large-truck crashes, 36 percent of fatal heavy-truck crashes, and 1533 percent of fatal-to-the-truck-occupant-only crashes have been attributed to driver fatigue (Knipling and Shelton, 1999). Again, these numbers are likely conservative and do not capture the subtle negative effects that "everyday" fatigue has on driver performance and crash risk.

In addition to crash data, survey data and more controlled research studies have also demonstrated the importance of maintaining alertness when driving. The challenge lies in the fact that almost everyone drives while tired or distracted on at least some occasions, and for some of us, it is more often than we may care to admit. Addressing the problem will necessarily require a broad-based, comprehensive approach involving roadway and environmental improvements, traffic law enforcement, and, perhaps most importantly, changing people's behaviors so that they are less likely to drive when fatigued or while engaged in potentially distracting activities.

Objectives of the Emphasis Area

The objectives for reducing crashes and crash-related injuries and deaths due to inattentive driving are to

  • Make roadways safer for drowsy and distracted drivers,
  • Provide safe stopping and resting areas,
  • Increase driver awareness of the risks of drowsy and distracted driving and promote driver focus, and
  • Implement programs that target populations at increased risk of drowsy or distracted driving crashes.

Exhibit I-2 lists these objectives and the strategies designed to meet them. In keeping with the goals of the AASHTO Strategic Highway Safety Plan, the strategies emphasize low-cost, short-term safety improvements for reducing collisions due to distracted and drowsy drivers.

The first objective draws heavily from two earlier guides: Volume 6, addressing run-off-road collisions, and Volume 4, addressing head-on collisions. The second objective also targets the road environment but from a different perspective—seeking to prevent a crash from occurring in the first place. The third objective is directed at the general driving population, whereas the fourth targets subpopulations known to be at increased risk of involvement in distracted or drowsy driving crashes. These high-risk populations include young drivers, drivers who work nighttimes or have irregular work schedules, commercial vehicle operators, persons with undiagnosed sleep disorders, and others.

For each objective, two or more specific strategies are identified. The strategies are intended for implementation by state DOTs, highway safety offices, law enforcement agencies, motor vehicle departments, and others.

Explanation of Objectives

The identified objectives and their respective strategies reflect the need to address the varying dimensions of the problem. Four fundamental objectives are evident from a review of research and basic understanding of the distracted and drowsy driving crash problem. The four objectives address (1) tailoring roadway infrastructure to respond to distracted or drowsy drivers; (2) enhancing the driving environment by increasing opportunities for rest or for attending to activities that otherwise might disrupt driving; (3) increasing general awareness of the safety problems caused by drowsy and distracted driving; and (4) targeting specific high-risk populations prone to drowsy or distracted driving.


Objectives and Strategies for Reducing Collisions Due to Driver Inattention

Targets of the Objectives

The first objective addresses changes to the roadway that either reduce the likelihood that an inattentive driver will crash or reduce the likely severity of inattention crashes once they do occur. This objective is most pertinent for state and local DOT engineers. The second objective addresses changes in the broader driving environment and specifically aims to reduce the occurrence of crashes due to driver inattention by providing safe places for drivers to stop and take a break from driving. While DOT planners are the primary target group for implementing this strategy, engineers, law enforcement, and highway safety officials can also contribute to its success.

The third objective focuses on the general driving population. Since distracted and fatigued driving are primarily behavioral issues, educating drivers, and working to create a change in public opinions about drowsy and distracted drivers, is key to reducing these types of crashes. Finally, the fourth objective addresses specific populations known to be at increased risk of drowsy and distracted driving crashes. Each objective has specific characteristics and needs that require more intensive individualized efforts to bring about the desired changes in behavior that will lower crash risk. Implementing educational interventions requires broad input and support from the highway safety community and draws upon both public and private resources.