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Driver fatigue: symptoms, cause and effects

Wednesday, July 31, 2013 by Chris Hocking

Being fatigued significantly increases the risk of a crash. It makes us less aware of what is happening on the road and impairs our ability to respond quickly and safely if a dangerous situation arises. Driver fatigue is believed to contribute to more than 30% of road crashes.

Symptoms of driver fatigue

It is very difficult for drivers to accurately assess their own level of fatigue. The ability to self- assess becomes increasingly impaired as you get more fatigued, however the self-confidence in this ability remains. Nevertheless, there are some warning signs to look out for, including:

  • Trouble focussing, or narrowing of attention
  • Head nodding, or inability to keep the eyes open
  • Not remembering the last few minutes
  • Poor judgement, slower reaction time
  • "Zoning out"
  • Daydreaming and wandering thoughts
  • Constant yawning or rubbing your eyes
  • Drifting in the lane

Keep in mind that if you are experiencing any of these symptoms of driver fatigue, it is very likely that your driving performance is already impaired.

Causes of driver fatigue

There are two main causes of driver fatigue:

  • Lack of quality/quantity of sleep
  • Driving at times of the day when you would normally be sleeping.

The end result is not getting enough sleep, which can lead to a build-up of a "sleep debt" – this is essentially the sleep that you 'owe' yourself. The only way to repay this debt is by sleeping.

Until you can catch up on lost sleep you will have a greater risk of having a fatigue-related accident.

A number of factors influence the likelihood that a driver will become fatigued, these include:

  • How long you have been awake (particularly beyond about 17 hours)
  • Time of day: your body and brain have a biological clock (circadian rhythm) that influences how alert or drowsy we are at certain times of the day
  • The quantity and quality of your last period of sleep
  • Your level of physical or mental activity at the time (eg long boring stretches of road make it difficult to maintain alertness and vigilance)
  • The presence of untreated sleep disorders (such as obstructive sleep apnea or narcolepsy)
  • Sedative drugs

  • Nobody is immune to the effects of driver fatigue, however some groups of people are more at risk than others:

  • Young drivers: the combination of inexperience and night driving
  • Shift workers and those working extended hours:  Shift workers are 6 times more likely to be in a fatigue-related crash, whether that be at work (operating machinery or vehicles) or commuting
  • Commercial drivers: Long distance driving, often at night
  • Business travellers: Drivers suffering from jet lag and crossing time zones often suffer from restricted and/or poor quality sleep

Effects and consequences of driver fatigue

As we have emphasised in other blog posts, the consequences of driver fatigue can be disastrous. 

Because fatigue impairs mental processing and decision making abilities, drivers can lapse into a "micro-sleep" without realising. This may only last a few seconds, but if it coincides with the need to perform some critical driving task (e.g. turning the wheel or responding to a stop signal), the risk of crashing is greatly increased.

These accidents typically involve a single vehicle that departs the driving lane and collides with another object, such as a tree beside the road or another vehicle.  The driver is often alone, having been driving for some hours, often between midnight and 6am.  The consequences of accidents attributed to driver fatigue are often the most serious in terms of death, injuries and property damage because the fatigued driver makes no attempt to avoid the impending crash.

This is why the effects of driver fatigue are so dangerous.

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