Focus on Fatigue

Drowsy Driving

By December 4, 2023 No Comments

Issue #79 – December 23

Welcome to Focus on Fatigue!

It’s December and the silly season is once again upon us. At this time of year many people attend a variety of Christmas parties, and other end of year celebrations. It can be easy to find ourselves getting behind the wheel of a car at the end of a long night when we’re feeling tired and eager to get home to bed. For shift workers, driving at odds times of the day or night, often while sleep deprived, can be an all too common occurrence at any time of the year.

This month, our Focus on Fatigue newsletter will examine the issue of Drowsy Driving, including how to recognise the symptoms and what you can do to increase your chances of arriving home safely.

InterDynamics would also like to take this opportunity to wish all our Focus on Fatigue readers a very happy and safe Christmas and New Year period.

The FRMS Team


Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).

Drowsy Driving

It’s more than keeping your eyes open

We all know how important it is to be sober when we get behind the wheel of a car. The consumption of alcohol impedes our driving performance, making us more likely to have an accident. So we are careful about how much we drink, how long since our last drink, or we abstain from drinking alcohol altogether if we know we’ll be driving. We get behind the wheel of our car at the end of a long day, or at the end of the party, and we’re tired but sober. Does this mean that we are safe to drive?

Fatigue impairs driving performance

Studies have shown that extended wakefulness can impair your ability to drive in a similar way to drinking too much alcohol. Often we underestimate the effect of drowsiness on our driving performance, or we believe that we can fight off sleepiness long enough to get home safely. Unfortunately, this is not always true. Estimates vary (due to data collection and location variations) but around 10-20% of fatal and serious crashes are attributed to driver fatigue, with some suggesting the real numbers may be higher. The National Road Safety Action Plan identifies that ‘fatigue is four times more likely to contribute to impairment than drugs or alcohol’.

But what is drowsy driving and how do we know if it’s happening to us? When we do experience drowsy driving, what can we do about it?

What are the warning signs of drowsy driving?

The Sleep Health Foundation lists the following as signs of drowsy driving:

  • Yawning
  • Struggling to keep eyes open or focused
  • Difficulty concentrating
  • Difficulty remembering the past few kilometres
  • Lane deviations
  • Variations in driving speed
  • Doing things to keep yourself alert – such as winding down the window or turning up air conditioning or music
  • Head nodding – this is end-stage drowsiness, indicating that you are already having micro-sleeps

The danger of microsleeps

The American Academy of Sleep Medicine defines a microsleep as ‘an episode lasting up to 30 seconds during which external stimuli are not perceived. The polysomnogram suddenly shifts from waking characteristics to sleep. Microsleeps are associated with excessive sleepiness and automatic behaviour.’

Microsleeps are most likely to happen to people who are sleep deprived and performing a monotonous task, such as driving a car. Imagine, just for a moment, the possible consequences of experiencing a microsleep when driving. It may last a fraction of a second, or up to 30 seconds. Your car is still moving, your eyes may even be open, but your brain is asleep. You don’t see the brake lights of the car in front of you come on, or the red light up ahead, or the curve in the road, or the fact that you’re drifting onto the wrong side of the road. When you wake up from the microsleep, assuming you haven’t already had an accident, the decision-making areas of your brain are not the first ones to come back online. Meaning that even more precious seconds may elapse before you can react to what is happening around you.

Perhaps the scariest thing about microsleeps is this: You may not even be aware that you had one. So you keep driving. And chances are, it happens again. You can’t choose not to have a microsleep. You are no longer in control.

What about general drowsiness, without microsleeps?

Studies have shown that falling asleep at the wheel is not the only way in which drowsy drivers are at risk. They are also more likely to report crossing lanes while driving, more likely to increase their average driving speed, more likely to be aggressive and may take more risks due to an impaired ability to assess situations.

Why are shift workers more likely to experience drowsy driving?

Shift workers have been found to be one of the groups most at risk of drowsy driving (along with young drivers, commercial truck drivers, those with untreated sleep disorders and those who use medicines that make them sleepy). Shift workers are more tired than non-shift workers during commuting. They get less sleep overall, resulting in increased levels of sleepiness. The sleep they do get tends to be of a lower quality because of the increase in day sleep. They often commute longer distances. Shift workers are also more likely to be driving at times when their circadian rhythm (internal biological clock) is telling them it’s time to sleep.

One study conducted by researchers from Brigham and Women’s Hospital found that shift workers were at a higher risk for drowsy driving crashes when driving during the day after a night shift. Even short commutes were shown to be potentially dangerous, with the risk increasing as the length of the drive increased. “Even veteran night shift workers were vulnerable to the risks associated with drowsy driving,” said one of the researchers involved in the study.

What should I do if I experience drowsiness while driving?

A variety of measures have been suggested over the years, some of which may work better than others.


If it’s not possible to pull over for an extended sleep, napping can be a useful short term remedy for drowsiness. A 5-min nap may improve a driver’s condition, but a 10-20 min nap is most beneficial. A 10-min nap in a reclined position, improves the ability of a driver for at least 1 hour. Napping for longer than 20 mins may not be advisable if you plan to drive straight away after, due to the onset of sleep inertia (that groggy feeling we can wake up with after napping).


Caffeine increases alertness in sleepy people. It has been suggested that a minimum of two cups of coffee is necessary for a positive effect on driving performance. The consumption of caffeine in drowsy drivers has been found to reduce lane deviations, potential crashes, and sleepiness for about an hour.

The coffee nap

Some researchers have explored the idea of combining napping and coffee. This involves drinking one-two cups of coffee quickly (so they can’t be too hot) and then immediately lying back for a short nap. By the time you are waking up from your nap, the caffeine will have entered your system. This combination was found to effectively increase alertness in drivers for an hour. In fact, the coffee nap was found to be more effective than either coffee or napping by themselves.

Other interventions

While other interventions are anecdotally popular, they have limited or no proven effectiveness. These include:

  • Keeping the interior of the car cool
  • Listening to talk or music on the radio
  • Varying the route a bit
  • Stopping to walk around for a while
  • Having a driving buddy

The real cure for drowsiness

It is always important to remember that the only thing that will truly cure you of drowsiness is sleep. Always take this into account before getting behind the wheel of your car. And if you really need to get somewhere and you are not safe to drive, keep yourself and other road users safe, and call a cab! The cost may be more in the short term, but less in the long term!


In The News

Blood Test for Sleepy Drivers Could Pave Way for Prosecutions

Linda Geddes, The Guardian, May 2023
A blood test to measure whether a driver who has caused an accident was impaired by lack of sleep could be available within two years.

Driver Fatigue – ‘A Dangerous Form of Impairment’ – Continues to Take Lives 

Tanya Mohn, Forbes, March 2023
Research found that many drivers may be unaware of how drowsy they are, and as a result, fail to take breaks because they may not realize the risks until it’s too late.

Sleep Deprived Medical Staff Pose Same Dangers on Roads as Drunk Drivers

Robin McKie, The Guardian, June 2022
Survey published in the journal Anaesthesia found 57% of respondents said they had experienced an accident or near miss when travelling home from a night shift.

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