Behaviours – Fatigue

Did You Know?

Each year on average, 78 people are killed and 8,532 are injured due to driver fatigue. Accidents generally occur in midafternoon or at nighttime, due to our internal clock.

Heavy vehicle drivers and fatigue

Fatigue is cited as the leading cause of accidents in an in-depth study of nearly 200 accidents that resulted in the death of a heavy vehicle driver in the United States.

Characteristics of accidents related to driver fatigue

  • Accidents occur at night (often after midnight), but also early in the morning or in midafternoon, when our bodies are programmed to rest.
  • Accidents are likely to cause serious injuries.
  • Accidents often involve a single vehicle veering off the road, but rear-end and head-on collisions are also very common.
  • Accidents occur in fast lanes.
  • Drivers make no attempt to avoid the accident.
  • Drivers are alone on board.

The effects of a long period of wakefulness: similar to the effects of alcohol

A laboratory study (Williamson and Feyer, 2000) compared the effects of a long period of wakefulness to the effects of alcohol (blood alcohol concentration):

  • Between 17 and 19 hours of wakefulness: Physical and mental capacities are comparable to those of a person with a blood alcohol concentration of 50 mg of alcohol/100 ml of blood (0.05)
  • After 24 hours of wakefulness: Physical and mental capacities are comparable to those of a person with a blood alcohol concentration of 100 mg of alcohol/100 ml of blood (0.10)

Main risk factors for driver fatigue

  • A sleep debt
  • An undiagnosed or untreated sleep disorder (apnea, insomnia, etc.)
  • The time of day: drowsiness is more frequent between midnight and 6 a.m. and 1 p.m. and 3 p.m.
  • The number of consecutive hours of wakefulness: after 17 hours of wakefulness, physical and mental performance decreases
  • The use of alcohol, drugs or medication, which amplify the effects of fatigue

Drivers most at risk

  • Heavy vehicle drivers
  • Drivers under age 30 and new drivers
  • Workers who have irregular schedules or long work days
  • Workers who work night shifts
  • Individuals who suffer from an undiagnosed or untreated sleep disorder
  • Individuals whose lifestyle affects the amount and quality of sleep they get

Sleep apnea

Sleep apnea is one of the most common sleep disorders.

Sleep apnea occurs when there are one or more interruptions in breathing during sleep. This contributes to decreased sleep quality and results in a sleep debt that can cause episodes of drowsiness during waking hours.

Who is most at risk?

  • Middle-aged men (age 45 or older)
  • People who are overweight
  • People who have a heart condition
  • Professional drivers: studies shows that most professional drivers are overweight males, making them more at risk than the rest of the population

Driver fatigue and your “internal clock”

Your internal clock, also called a biological clock or circadian rhythm, regulates your body temperature, hormone secretion, heart rate, blood pressure and digestion in addition to your sleep cycle.

The internal clock follows a cycle that repeats about every 24 hours. It is directly influenced by light and darkness, i.e. by day and night.

Dips in your internal clock cycle occur between midnight and 6 a.m. and, to a lesser degree, between 1 p.m. and 3 p.m. During these periods, your metabolism slows, alertness decreases and fatigue is more acutely felt.

The internal clock, also called a biological clock or circadian rhythm, follows a cycle that repeats about every 24 hours. Dips in your internal clock cycle occur between midnight and 6 a.m. and, to a lesser degree, between 1 p.m. and 3 p.m.