Risk Factors

Fatigue is a biological state that neither willpower, nor experience nor motivation can overcome or compensate for. Various risk factors influence your level of fatigue.

Generally speaking, drivers are more or less at risk of being involved in a fatigue-related accident based on the following factors:

  • length of wakefulness
  • sleep debt
  • length of the trip
  • time of day and their biological clock
  • undiagnosed or untreated sleep disorders
  • health problems that result in fatigue
  • the use of alcohol, drugs or medication

When these factors are combined, the risk becomes even greater. Respect your own limits regarding fatigue and sleep!

Fatigue does not affect everyone equally

Whereas some people feel more alert in the morning than at night, the opposite is true for others. Some people also do not cope with fatigue as well as others for various reasons, including their age, state of health, type of employment, sleep habits, diet, etc.

Length of wakefulness

The longer you stay awake, the more your abilities decrease. They can even decrease to a level normally associated with excessive alcohol intake. In fact, “sleep pressure” begins building up as soon as you wake up.

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).

Sleep debt

Most adults require 7 to 9 hours of sleep each night to be in good mental and physical shape. If you don't get enough sleep, you will accumulate a sleep debt. To pay this debt back, there is only one true solution: sleep!

According to a recent study (Maia, Grandner et al., 2013), individuals who sleep 6 hours or less per night are twice as likely to experience drowsiness while driving, while those who sleep 5 hours or less per night are 4 times as likely to experience drowsiness while driving.

Rest periods and short naps help you recuperate temporarily, but cannot replace a good night's sleep. Restorative sleep needs to occur in a calm place, be continuous and occur at night, between 10 p.m. and 7 a.m.

Trip length

The longer the trip, the higher the risk of a fatigue-related accident. Long trips decrease the cognitive capacities required to drive a vehicle. Drivers must therefore plan for sufficient rest periods during long trips (Ping-Huang Ting et al., 2008).

Time of day and the biological clock

The human body is programmed to sleep at night and stay awake during the day, regardless of a person's activities. This phenomenon is known as the circadian rhythm, internal clock or biological clock.

This clock regulates body temperature, hormone secretion, heart rate, blood pressure, digestion and sleep cycles. It is influenced by light, and the cycle is repeated about every 24 hours.

This clock is also responsible for the fact that alertness decreases and fatigue increases at certain times of day.

Times when the risk of falling asleep at the wheel are greater

  • At night, especially between midnight and 6 a.m.
  • Early to midafternoon, between 1 p.m. and 3 p.m.

Medical problems and fatigue

Severe fatigue can be a sign of a health problem. For example, this can occur in cases of:

  • heart failure
  • chronic obstructive pulmonary disease (COPD) 
  • sleep apnea
  • multiple sclerosis
  • anxiety or depressive disorders
  • diabetes or anemia
  • thyroid disease
  • chronic pain
  • inflammatory disease
  • cancer

Talk to your doctor or other health care professionals who can determine the cause of your fatigue. In most cases, a health care professional can review your medication and optimize your treatment. Should fatigue unfortunately be inherent to your condition, learn how to manage it with the help of your attending health care team. Plan to only drive when your energy level is higher and schedule enough time to complete your activity, including travel time. 

Undiagnosed or untreated sleep disorders

There are several dozen types of sleep disorders. Insomnia and sleep apnea are the most common.

Almost everyone may suffer from occasional insomnia – it is the most common sleep disorder. Unfortunately, for some, insomnia is a chronic condition.

Sleep apnea may take several forms and affects a relatively significant portion of the population. However, most of the people who suffer from sleep apnea remain undiagnosed.

If you have trouble sleeping or staying asleep, or if you often feel tired during the day, you should consult a physician.

Use of alcohol, drugs or medication and fatigue

Alcohol, drugs and medication may amplify the effects of fatigue and vice versa. See our section on drugs and medication for more information.

Last update: October  5, 2022