Focus on Fatigue

Focus on Fatigue, Issue 38: Drowsy driving

By December 1, 2015 No Comments

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 subscribers as very happy and safe Christmas and New Year period.

The FRMS Team

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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).

Feature Article

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. Because of this, we are careful about how much we drink, what we’ve eaten while drinking, 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?

In our September issue of Focus on Fatigue we examined the links between drunk driving and drowsy driving and discovered that 17-19 hours of wakefulness is equivalent to a blood alcohol concentration of 0.05%. 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. An Australian study estimated that up to 33% of crashes in the general population can be attributed to sleepiness. It’s believed that for shift workers this number may be higher.

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 National Sleep Foundation of America give the following symptoms of drowsy driving:

  • Difficulty focusing, frequent blinking, or heavy eyelids
  • Daydreaming; wandering/disconnected thoughts
  • Trouble remembering the last few miles driven; missing exits or traffic signs
  • Yawning repeatedly or rubbing your eyes
  • Trouble keeping your head up
  • Drifting from your lane, tailgating, or hitting a shoulder rumble strip
  • Feeling restless and irritable

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 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.

In a new study, released this month, it was 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 by researchers over the years, some of which may work better than others.

  • Napping – If it’s not possible to pull over for an extended sleep, napping is the most effectiveness remedy for drowsiness. A 5-min nap will improve a driver’s condition, but a 10-15 min nap is the most beneficial. A 10-min nap in a reclined position, improves the ability of a driver for 1-2 hours. Napping for longer than 15-20 mins is not advisable due to the onset of sleep inertia (that groggy feeling we can wake up with after napping).
  • Caffeine – 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 have been suggested but are yet to be consistenly proven effective. 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

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.


  • American Academy of Sleep Medicine (2001) The International Classification of Sleep Disorders, Revised. American Academy of Sleep Medicine. Westchester, IL.
  • Caba, J. (2015) Night shift workers are at an increased risk for car crashes, even during daytime commute. Medical Daily, accessed 21 December 2015.
  • Milla, L. D., Rogers, N., and Akerstedt, T. (2012) Sleepiness, long distance commuting and night work as predictors of driving performance. PlosOne, 7(9).
  • National Sleep Foundation (2013) Drowsy driving. National Sleep Foundation Website. Accessed on: 24/12/13 from
  • NCSDR/NHTSA Expert Panel on Driver Fatigue and Sleepiness (1998) Drowsy driving and automobile crashes: Report and recommendations. National Highway Traffic Safety Administration.
  • Orzel-Gryglewska, J. (2010) Consequences of sleep deprivation. International Journal of Occupational Medicine and Environmental Health, 23(1), 95-114.
  • Pierce, R. J. (1999) Driver sleepiness: Occupational screening and the physician’s role. Australian and New Zealand Journal of Medicine, 29, 658-661. In: Conner, J., Norton, R., Ameratunga, S., Robinson, E., Civil, I., Dunn, R., Bailey, J., and Jackson, R. (2002) Driver sleepiness and risk of serious injury to car occupants: Population based case control study. British Medical Journal, 324.
  • Reyner, L. A. and Horne, J. A. (1997) Suppression of sleepiness in drivers: Combination of caffeine with a short nap. Psychophysiology, 34(6), 721-725.
  • Rogers, A., Holmes, S., and Spencer, M. (2001) The effect of shiftwork on driving to and from work. Journal of Human Ergology (Tokyo), 30(1-2), 131-136.

InterDynamics News

Conferences and presentations

This section outlines recent and upcoming InterDynamics speaking engagements and/or conferences that we recommend and will be attending.

Human Factors for Transport Safety Investigators, Australian Transport Safety Bureau (ATSB), Canberra, 2nd-6th November 2015

In November, InterDynamics attended the Human Factors for Transport Safety Investigators course, run by the Australian Transport Safety Bureau (ATSB) in Canberra.

The Course Objectives were to provide participants with an awareness of:

  • the key terms and concepts used in human factors;
  • basic human performance capabilities and limitations;
  • the factors that influence human performance;
  • the importance of human factors in transport safety;
  • how human factors issues can be considered during an investigation; and
  • where to find expertise on more complex human factors issues.

The ATSB Human Factors course provides participants with a general overview of human factors in safety-critical systems, including the aviation, marine, and rail industries.

Human Factors is the multi-disciplinary science that applies knowledge about the capabilities and limitations of human performance to all aspects of the design, manufacture, operation, and maintenance of products and systems.

After any accident or incident, a thorough operational and technical investigation is essential to determine what happened during the occurrence. However, very often, it is only by investigating the possible role of human factors, at both the individual and organisational level, that it can be determined how and why the events occurred. Only then can appropriate safety action be taken.

The ATSB is a leader in the application of human factors to transport safety investigations, and has developed a highly regarded Human Factors for Transport Safety Investigators course. While the course is intended primarily for ATSB personnel, a limited number of places are available to industry participants from the aviation, marine and rail industries.

InterDynamics would like to encourage all of our Focus on Fatigue Newsletter readers to attend such a course as part of your FRMS operation and development. Please check with your local investigation board or regulator for international readers.

In the News

Provided below are a selection of articles and videos from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Article: The dangers of drowsy driving

by Dr Michael Breus, The Huffington Post (7 December 2013)

New data from the AAA Foundation for Traffic Safety indicates that a significant number of us are driving when experiencing excessive and dangerous fatigue. According to a report released by AAA in November, 28 percent of drivers surveyed said they’d struggled to keep their eyes open while behind the wheel at least once in the past month. Among young drivers, the tendency to drive while drowsy is even higher: 33 percent of drivers ages 19-24 admitted to struggling to stay awake while driving in the last 30 days.

Article: Night shift workers are at an increased risk for car crashes, even during daytime commute

by Justin Caba, Medical Daily (21 December 2015)

Night shift workers may be at an increased risk for certain conditions, such as heart disease and type 2 diabetes, but the effects of an impaired sleep schedule can be even more devastating and immediate. A recent study conducted by researchers from Brigham and Women’s Hospital has found that people who drive home after working a night shift suffer from disruptions to their sleep-wake cycles and insufficient sleep during the night which, subsequently, results in a higher risk for drowsy driving crashes.

Infographic: Awake at the wheel

by American Academy of Sleep Medicine (28 September 2015)

The National Healthy Sleep Awareness Project urges every driver to take responsibility for staying “Awake at the Wheel” by making it a daily priority to get sufficient sleep, refusing to drive when sleep deprived, recognizing the signs of drowsiness, and pulling off the road to a safe location when sleepy.

Video: Microsleeps while driving

by Fatigue Training Online (16 February 2011)

Watch what happens when you are fatigued and you start having microsleeps whilst trying to perform some basic driving manoeuvres.

Video: Tips to avoid driver fatigue

by RACQ Official (16 July 2013)

What do loud music, energy drinks, freezing air conditioning and yelling at the top of your lungs all have in common? They’re all commonly used tactics by tired drivers to stay awake at the wheel — and in this episode of RACQ TV we take a closer look at the risks many tired motorists are taking on a daily basis. Unlike the other ‘fatal five’ risks – distraction, speed, alcohol and not wearing a seatbelt – it is almost impossible to police fatigue. As individuals, it’s up to us to be responsible and not push the limit. So — how does fatigue affect your driving and what can you do to offset its effects?


Article: Drowsy driving also worsens driver distraction

Anderson, C. and Horne, J. A. (2013) Driving drowsy also worsens driver distraction. Sleep Medicine, 14(5), 466-468.


Objectives: Laboratory-based studies show that drowsiness increases the propensity to become distracted. As this phenomenon has not been investigated in drowsy drivers, we underwent a pilot study under realistic monotonous driving conditions to see if distraction was more apparent when drowsy; if so, how does it affect driving performance?

Methods: A repeated measures counterbalanced design whereby participants drove for two hours in a fully interactive car simulator during the bi circadian afternoon drive, after a night of either normal (baseline) or restricted sleep to five hours (sleep restriction). Videos of drivers’ faces were analysed blind for short (<3 s) and long (>3 s) distractions, in which drivers took their eyes off the road ahead. These results were compared with the likelihood of simultaneous lane-drifting incidents, when at least two wheels left the driving lane.

Results: More distractions occurred after restricted sleep (p < 0.005) for both short and long distractions (p < 0.05). There was an overall significant (p < 0.02) positive correlation between distractions and driving incidents for both conditions but with significantly more distraction-related incidents after sleep restriction (p < 0.03).

Conclusions: Following restricted sleep, drivers had an increased propensity to become distracted, which was associated with an increased likelihood of poor driving performance as evidenced by the car leaving the driving lane.

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