What is Fatigue Impairment?

Most people are aware of the dangers of drinking and driving but don’t realize that drowsy driving can be just as fatal. Like alcohol, fatigue impairment slows reaction time, decreases awareness, impairs judgment and increases the risk of crashing.

Fatigue is a general term commonly used to describe the experience of being “sleepy,” “tired,” “drowsy,” or “exhausted.” While all of these terms have different meanings in research and clinical settings, they tend to be used interchangeably in the traffic safety and transportation fields.

1. Definition

Fatigue is the progressive reduction in physical and mental alertness which leads to sleepiness and sleep. Fatigue become problematic when it compromises a driver’s reflexes and ability to concentrate or use judgement.

2. Effects

  • decreases vigilance, concentration and attention
  • judgement is altered and quality of decisions affected
  • reaction time slows
  • memory affected
  • sleepiness and periods of mico-sleeps (lasting 4 to 6 seconds)
  • sleep

3. Causes of fatigue

Driver-related causes: biological clock, personal typology (early-riser or night-owl, introvert or extravert), state of health (physical and mental), number of waking hours, quantity and quality of sleep, diet, physical condition, family life, age, etc.

Work-related causes: corporate culture, time of day and length of work period, shift schedules, night work, physical effort required, etc.

Environmentally-related causes: ergonomics of the vehicle, highway and weather conditions, availability of rest areas, highway monotony, etc.

4. Aggravating factors

A) Time of the day (internal, circadian, biological clock)

  • We all have a circadian clock located in the area of the brain called the hypothalamus.
  • This clock regulates body temperature, hormonal secretion, heart rates, blood pressure, digestion – as well as the sleep cycle. It follows a cycle that is repeated approximately every 24 hours and is influenced by such external factors as light and darkness.
  • The sleep cycle fluctuates throughout the day. People experience an initial loss of alertness and increasing drowsiness between 1:00 p.m. and 3:00 p.m. and another at night between midnight and dawn. This second drop in alertness is, however, considerably more pronounced.
  • Whatever a person is doing, fatigue occurs during these two low points in the cycle.

B) Number of waking hours

  • After 17 hours of being awake, a person’s concentration and reflexes diminish quickly.
  • The longer subjects remain awake for extended periods of time, the greater the degradation of their performance becomes, reaching levels usually associated with excessive alcohol consumption (Lamond, Dawson, Australia, 1998); (Feyer, Williamson, Sadural & Friswell, Australia, 2001).
  • In 40% of fatigue-related accidents, the driver had been awake for more than 17 hours (Stutts et al., USA, 1999).

C) Accumulated sleep deficit

  • 32% of North Americans sleep less than six hours a day and thus build up a sleep deficit (Johnson, 1998).
  • The results of research conducted by Stutts, Wilkins and Vaughn (1999) with 1,400 drivers showed that half (50%) of drivers involved in a fatigue-related accident had had less than six hours of sleep the night before the accident.
  • Carskadon (2000) observed that performance begins to deteriorate after a two-hour sleep deficit.
  • Every sleep deficit needs to be made up through sleep.

D) Sleep disorders (sleep apnea, narcolepsy, insomnia, etc.)

Example: Sleep apnea

  • Particularly prevalent in men aged 45 and over who are overweight (3% of women and 5% of men, about 15% of professional drivers)
    Loud and interrupted snoring
  • Repeated stopping of breathing throughout the night, resulting in non-restful sleep
  • Excessive daytime drowsiness and fatigue, irritability, loss of libido, etc.
  • An easily diagnosed and highly treatable problem (through Continuous Positive Air Pressure, an oral device or surgery)

E) Consumption of alcohol, medications or other drugs

A dangerous combination. The effects of fatigue are greatly intensified when alcohol (even in very small amounts) or other drugs are consumed. (These factors have a cumulative effect and any combination thereof can greatly increase the risk of an accident caused by fatigue.)

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