Impacts, Causes, and Warning Signs

Physical and mental fatigue both reduce a worker’s ability to safely perform essential driving-related duties. They’re a leading contributing cause to vehicle crashes – right up there with distractions, speed, and impairment. Insufficient quantity and quality of sleep are the two most common causes of fatigue.

How Fatigue Impacts Drivers

Physical fatigue results from strenuous activities that can exhaust your muscles. You may be unable to respond as quickly or as effectively as usual when driving.

Mental fatigue is the greater concern for most drivers. It decreases the ability to perform key driving tasks.

Even an extra fraction of a second in reaction time can be the difference between a near miss and a serious, costly crash.

Risks to drivers who are mentally and/or physically fatigued include:

  • Increased tendency to take risks
  • Increased likelihood of forgetting or ignoring normal checks or procedures
  • Decreased ability to absorb critical driving information and respond to it
  • Diminished judgment when deciding what actions to take to address a hazard
  • Reduced problem solving abilities and manual dexterity
  • Reduced ability to judge distance, speed, and time

Main Causes of Fatigue

Poor sleep and a lack of sleep are the most common factors contributing to driver fatigue. They can disrupt the natural 24-hour sleep/wake cycle, known as a circadian rhythm. Factors in work and everyday life can also contribute to driver fatigue. These include:

  • Work Tasks, Environment, and Schedule

    It doesn’t matter if workers are driving or not. They can be fatigued by any part of their job that is repetitive, boring, or strenuous. Complex tasks, and sustained mental or physical effort, also can cause fatigue. Driving for long hours requires constant concentration, for example.

    The workplace environment – in a motor vehicle or elsewhere – can make drivers drowsy. Temperature, vibration, and light and noise levels all affect our alertness. So do humidity and low stimulation.

    Even a worker’s schedule can create fatigue. Night shifts, back-to-back shifts, overtime, and rotating shifts can affect the sleep/wake cycle. Working long or irregular hours can throw off circadian rhythms too.

  • Being Awake for Long Hours

    The effects of driving after staying awake for long periods of time are similar to the effects of drinking alcohol. Both leave drivers impaired.
  • Medications

    Some prescription medications and over-the-counter medicines contain caffeine or other stimulants that can interrupt normal sleep patterns. The list includes heart, blood pressure, and asthma drugs. Pain relievers, cold decongestants, antihistamines, and diet pills also can affect sleep. Some medications can induce drowsiness.
  • Stress

    Demanding workdays can leave drivers feeling stressed out, frustrated, and exhausted. Stress from a driver’s personal life also takes its toll on driving performance.
  • Inadequate Sleep

    Getting less than 7.5 to 8.5 hours of sleep every night can leave drivers fatigued. Losing one hour of sleep each night creates a sleep debt of 5 hours after 5 days. Drivers need an equivalent amount of restorative sleep to make up for it.

    Sleep apnea, insomnia, night terrors, and other disorders greatly reduce sleep quality.

Warning Signs of Fatigue

Fatigue has many common symptoms but is difficult for drivers to self-assess. Tell-tale signs include the following:

  • Feeling sleepy, drowsy, or exhausted
  • Yawning
  • Sore, heavy, droopy, or blood-shot eyes
  • Slower than normal reflexes and reaction times
  • Impatience or irritability
  • Aching, stiff, or sore muscles, or cramps
  • Lack of motivation
  • Indecisiveness
  • Daydreaming, decreased ability to focus or concentrate

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Driver Fatigue Overview

Impacts, Causes, and Warning Signs

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