The Fatal Effects of Driver Fatigue

Driver fatigue is one of the biggest killers on the roads, playing a role in approximately 13% of Australian road accident deaths between 2012 and 2016. It is also one of the hardest accident causes to combat.

In fact, driver fatigue poses a number of unique challenges to public authorities in their efforts to reduce the road toll. Fatigued driving is hard to police, and may affect drivers who are otherwise very responsible on the road. It is also a major risk factor for long haul heavy vehicle drivers, whose vehicles have a tendency to inflict high casualty rates when they cause accidents.

Furthermore, while most drivers are aware that driving while fatigued is a bad idea, the majority of people are most likely to be on the roads in the mornings and the late afternoons – the two periods of day in which they are highly likely to be fatigued. It can also be very hard for a driver to determine when their fatigue levels reach the point where they pose an accident risk.

Reducing the risk of accidents from driver fatigue therefore places the onus on drivers to understand the impact of fatigue on their driving ability, and to take the necessary precautions when they believe that they may be too tired to drive.

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What is driver fatigue?

Driver fatigue can impact driver behaviour in numerous ways. While driving with some level of fatigue, for example at the end of a work week, is normal, driver fatigue becomes dangerous when:

  • it increases the amount of time a driver takes to notice a road hazard
  • it increases the amount of time a driver takes to respond appropriately to situations encountered on the road, from traffic signals to the actions of other drivers
  • it results in brief lapses of consciousness, known as microsleep, in which the driver nods off for a split second before awakening.

Any one of the above is sufficient to increase the risk of an accident. However, as a driver becomes more fatigued they are more likely to experience all of these effects on their driving behaviour, exponentially increasing their risk of causing, or becoming involved in, an accident.

It is also important to note that driver fatigue is not only related to sleep deprivation. Driver fatigue can also arise in situations where driving is highly monotonous, like on long distance journeys. The simple monotony of these journeys can have the same impact on driver attention as sleep deprivation and exhaustion.

Why fatigued driving is dangerous

Driving while fatigued impacts attention and reaction times, and paying attention to the road and responding swiftly to hazards are both critical components of smart, safe driving.


Microsleep typically occurs in situations where an individual is so fatigued they have to consciously battle to remain awake. During an episode of microsleep an individual will lose consciousness for a periods ranging from a fraction of a second to 30 seconds.

There are two things that make microsleep highly dangerous to drivers.

Firstly, microsleep results in complete inattention for the period in which the driver loses consciousness. As with other forms of inattention this can result in a driver covering potentially large distances without the ability to respond appropriately to any hazards that arise during this period. For example two seconds of microsleep while travelling at 110km/h will result in the driver travelling over 60 meters without being able to respond to any hazards.

The other major danger associated with microsleep is that drivers may be completely unaware that they are periodically slipping out of wakefulness. Drivers who are experiencing microsleep will typically believe that they are fully conscious, and at worst will perceive their episodes of microsleep as temporary lapses in attention. This lack of awareness of what is happening to them greatly amplifies the risks of an episode of microsleep leading to an accident.

Reduced driver performance

We already noted that sleep deprivation leads to increases in reaction time, an issue noted in numerous studies. Fatigued drivers take longer to react hazards.

However, reaction time isn’t the only thing affected by sleep deprivation. Fatigue can result in impaired attentionpsychomotor skillsmoral judgement, and decision making. All of these are critical in assessing and responding to unexpected threats that can arise while driving, and create multiple overlapping performance deficits, each of which increases accident risk independently.

In combination what this means is that a fatigued driver will take longer to notice an unexpected hazard on the road, take longer to respond to that hazard, find it harder to spontaneously make the right decision in the split second they will have to avoid an accident  and suffer reduced physical performance in executing the actions required to avoid an accident.

Fatigued driving fatality statistics in Australia

A number of Australian states record driver fatigue as an accident cause, although this is not recorded in all states and territories, or reported at a national level.

For the states that do record this data, the following table indicates the percentage road accident deaths between 2012 and 2016 where fatigue was a causative factor.

Driver fatigue accident fatalities



When these figures are combined, fatigue claimed 12.9% of all deaths on the roads on these states for the years under consideration.

What this means for you

It is impossible to avoid fatigue at all times, therefore avoiding the risks associated with driver fatiguerequires you to recognize when your fatigue levels are likely to pose a threat to both you and other road users. Some basic planning around trips that are likely to involve monotony is also a quick and easy way to significantly reduce the risk of involvement in an accident caused by fatigue.

Don’t drive if sleep deprived

Sleep deprivation can occur in a few different contexts and patterns.

You should avoid driving if you:

  • have gone 24 hours or more without sleep
  • have experienced a pattern of broken or inadequate sleep over several days – in these cases losing even a couple of hours a night has a cumulative impact on your driving ability
  • are on any medication that is known to lead to drowsiness, this can include a variety of over the counter and prescription medications ranging from painkillers to antihistamines.

Recognise the warning signs of microsleep

Even if you don’t meet the above criteria, then you should still pay attention to the following critical signs of fatigue which typically occur in people likely to enter microsleep:

  • drooping eyelids
  • slowly closing eyes
  • blurred vision
  • a feeling of needing to fight to remain awake
  • a nodding head, or having to pull your head up to retain focus on the road
  • constant yawning
  • lapses in memory
  • having to repeatedly and suddenly correct lane departures
  • missing traffic signals.

Don’t wait to experience all of these symptoms before you pull over. Any one of these signs indicates that you’re probably too tired to drive a vehicle.

Stay off the road if you are drowsy

If you observe any of the signs listed above, then drive your vehicle to the nearest point where you can stop it legally without obstructing traffic.

You then have a few options available to you:

  • Set an alarm and take a 25-30 minute nap – this has the greatest probability of refreshing you. Avoid a longer nap unless you have time for a 90 minute nap, which will allow your body to enter a full cycle of REM sleep, and will provide the greatest overall benefit. Best of all get a proper night’s sleep before getting back in your car.
  • Drink two cans of an energy drink. Two drinks is believed to provide the maximum benefit in terms of improved alertness. Drivers should still rest 20 minutes after consuming these drinks to allow them to take effect. It can also be beneficial to attempt a 20 minute nap immediately after consuming the energy drinks, as this will further improve alertness levels on waking. Note that the benefits of consuming energy drinks will drop away after 90 minutes. Furthermore, repeated use of energy drinks to combat fatigue can reduce effectiveness and result in undesired and potentially harmful physical side-effects.
  • If you are severely fatigued, the best option is to park your car in a parking facility. Then use another means of transport to reach your destination or book accommodation where you can catch up on the sleep you need.

Avoid situations that increase the risk of driver fatigue

Driver fatigue can be avoided altogether, particularly on long distance trips where driving is likely to be monotonous and extend over long periods of time.

The following can all make your trips safer:

  • plan longer distance trips, allowing for stops every two hours
  • plan overnight stops on longer road journeys
  • avoid driving between midnight and 7am – the period between 2am and 6am is particularly dangerous as your body expects you to be asleep
  • share driving responsibilities, giving yourself the option to take a break as soon as you begin feeling the effects of fatigue.

Finally, pay attention to the behaviour of other drivers, particularly on long distance journeys or if you are on the road between midnight and 7am. The driving of fatigued drivers can resemble that of drunk drivers, with lane departures and other erratic behaviours. If you suspect the driver of a car in front of you is fatigued and at risk of an accident, increase your following distance and if possible summon road traffic authorities. Do not attempt to overtake the vehicle unless it is safe to do so.

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