In general, since all humans require sleep on a daily basis, any driver can succumb to fatigue or be at higher risk for experiencing a decrease of alertness or microsleep when they have not obtained adequate sleep (both in quality and quantity).

There are many underlying causes of sleepiness, drowsiness, fatigue and drowsy driving. They include sleep loss from restriction, interruption or fragmentation; chronic sleep debt; circadian factors associated with driving patterns or work schedules; time on task; the use of sedating medications; and the consumption of alcohol when already tired. These factors have cumulative effects and a combination of any of these increases crash risk greatly.

The risk of having a crash due to drowsy driving is not uniformly distributed across the population. This is due to two factors. First, crashes tend to occur at times in keeping with one’s circadian rhythms when sleepiness is most pronounced, for example, during the night and in the mid-afternoon. Thus individuals who drive at night are much more likely to have fall-asleep crashes. Second, people who are excessively sleepy either because of lifestyle factors or because of an untreated sleep disorder are more likely to have crashes related to excessive daytime sleepiness. Research has identified young males, shift workers, commercial drivers and people with untreated sleep disorders or with short-term or chronic sleep deprivation as being at increased risk for having a fall-asleep crash.

Specific At-Risk Groups

  • Young people-especially males under age 26
  • Shift workers and people with long work hours-working the night shift increases your risk by nearly 6 times; rotating-shift workers and people working more than 60 hours a week need to be particularly careful
  • Commercial drivers-especially long-haul drivers – at least 15% of all heavy truck crashes involve fatigue
  • People with undiagnosed or untreated disorders-people with untreated obstructive sleep apnea have been shown to have up to a seven times increased risk of falling asleep at the wheel
  • Business travelers-who spend many hours driving or may be jet lagged

Are You at Risk?

Before you drive, consider whether you are:

  • Sleep-deprived or fatigued (6 hours of sleep or less triples your risk)
  • Suffering from sleep loss (insomnia), poor quality sleep, or a sleep debt
  • Driving long distances without proper rest breaks
  • Driving through the night, mid-afternoon or when you would normally be asleep
  • Taking sedating medications (antidepressants, cold tablets, antihistamines)
  • Working more than 60 hours a week (increases your risk by 40%)
  • Working more than one job and your main job involves shift work
  • Drinking even small amounts of alcohol
  • Driving alone or on a long, rural, dark or boring road