Drowsy Driving


Pillow - You can't fight Sleep

Drowsy driving is dangerous and potentially deadly. If you're already behind the wheel when you start to feel drowsy, the best remedy is to pull over and have a 15 minute powernap.

You may think you can push through drowsiness, but you can't fight sleep. All day, sleep inducing chemicals build up in your brain. They eventually reach a tipping point, sending you off to sleep, which can happen any time and anywhere. The best way to avoid drowsy driving is to get a good night's sleep.

Fatigue, including ‘drowsy driving’ is a contributing factor in between 16-20% of all road crashes in Victoria.

  • Plan a break at least every two hours
  • Consider swapping drivers
  • Pull over for a 15 minute powernap
  • Avoid driving at times when you would usually be sleeping
  • Aim to get enough quality sleep before driving – regardless of whether the trip is a long or short one. A healthy adult needs on average between 7-9 hours of sleep to function properly.
  • Visit a Towards Zero SES Pit Stop


Thank you to the staff at the Cooperative Research Centre For Alertness, Safety and Productivity for their assistance in compiling the below information.

Q: What is the science behind sleep?

A: Sleep is regulated by two main processes: a circadian process and a homeostatic process. This is known as the two process model of sleep. Interactions between these processes determine the timing, duration and quality of sleep1.

Homeostatic process of sleep:

The sleep homeostat is responsible for the growing pressure to sleep that builds up over time while an individual is awake. With each hour an individual is awake, the propensity to sleep (or likelihood of falling asleep) increases. During sleep, sleep pressure dissipates and starts to build again after we wake up. If not enough sleep is achieved during the sleep episode, a 'sleep debt' starts to accumulate. This 'debt' can only be 'repaid' with more sleep.

Circadian process of sleep determination:

Interacting closely with the homeostatic system is the circadian timing system. Controlled by an internal biological clock, or circadian pacemaker, this system causes rhythmic fluctuations in sleep pressure and several other biological functions over a ~24 hour period. Circadian means 'about a day', as this process represents the changes in sleep propensity across the 24 hour day.

The homeostatic and circadian systems interact to promote sleep and wakefulness throughout the 24-hour day. The homeostatic signal for sleep is dramatically increased after 16 hours of wake2, which coincides with the night-time circadian signal for sleep. At this point the propensity for sleep is high. The combined effect of these two systems results in a consolidated sleep episode of approximately 8 hours in duration3, when the sleep episode occurs at the optimal time of day.

Q: What chemicals are involved in sleep?

A: Falling asleep momentarily can happen to anyone. Many of us may have experienced this overwhelming drive to sleep after staying up late, getting up early, or after having a bad night's sleep. As described above (see Homeostatic process), sleep drive continues to increase while we are awake, and is reduced only during sleep. Sleep drive can be measured indirectly through monitoring of brain activity, for example a slowing of neuronal activity levels in the brain. However, experts suggest that a build-up of neurochemicals in the brain is the cause of increasing sleep drive. One example is adenosine, a by-product of energy consumption by brain cells. As our brains work during the day this chemical increases and then decreases during sleep4.

The process of falling asleep is a neurochemical process. Maintaining alertness or arousal is based on a number of neurochemical outputs from the ascending activating system located in the brain stem. These may be cholinergic inputs which transmit to the thalamus (the gateway for incoming information) or monaminergic inputs from the arousal centres which transmit directly to the cortex4. Together, these arousal pathways transmit a number of neurochemicals to the cortex which maintain arousal and also allow for the processing of and response to visual and auditory stimuli. Sleep occurs when a neurochemical known as GABA (gamma-amino butyric acid) is released in the ventro-lateral pre-optic area (the 'VLPO'). GABA inhibits (or switches off) the arousal centres so when released results in wake being switched OFF and sleep being switched ON. This is known as the "sleep-wake switch".

The 24-hour biological clock (circadian timing system) controls the timing of melatonin secretion by the pineal gland. Melatonin is a biological signal to the brain that it is night-time and is closely associated with increased feelings of sleepiness/drowsiness in humans. As an example of the effects of melatonin, melatonin pills can increase melatonin levels in the brain and induce drowsiness.

Q: Can I consciously control when I will fall asleep?

A: When attempting to fall asleep as a voluntary process (i.e., as we might do each night in bed), the transition from a wake state to a sleep state is both transitory and dynamic. That is, we wax and wane from N1 sleep back to wakefulness back to N1 sleep again and so on before eventually we remain in a constant sleep state. This sleep maintenance is typically driven by the presence of sleep spindles characteristic of N2 sleep.

When attempting to stay awake when sleep drive is high, an individual might experience involuntary moments of sleep. The process of falling asleep involuntary is the same – the brain transitions from a wake state to a sleep state and back again rapidly. However, in this case instead of the brain progressing to N2, it typically reverts back to wake. This is known as a 'microsleep'. When sleep drive is high, an individual experiences high levels of drowsiness. This manifests in a multitude of ways (as detailed on page 7 below). Drowsiness can therefore be considered a period along the sleep-wake continuum categories as wake (although alertness is poor) with brief periods of sleep.

Q: What causes drowsiness?

A: Drowsiness is largely caused by the interaction between homoestatic and circadian process of sleep and alertness regulation. As such, drowsiness is induced by extended time awake or staying awake beyond the typical bedtime; inadequate sleep the previous night; chronic restriction of sleep over a period of several days; presence of a sleep disorders affecting sleep quality; and immediately upon awakening especially after inadequate sleep or when awoken during the night-time hours.

Q: What are the signs of drowsiness?

A: Drowsiness can be identified by a number of physical and behavioural signs5:

Behavioural signs of drowsiness:

  • Difficulty focusing, shortened attention span
  • Slower reaction times
  • Poor concentration and reduced alertness
  • Mood changes (including irritability)
  • Reduced awareness of the environment and situation
  • Daydreaming or wandering/disconnected thoughts
  • Increased likelihood of mentally 'stalling' or fixating on one thought
  • Increase in errors
  • When driving: trouble remembering the last few miles driven; missing exits or traffic signs
  • When driving: drifting from your lane, tailgating, hitting a shoulder rumble strip or difficulty maintaining a consistent, correct speed.
  • When driving: seeking stimulation in an effort to remain awake, such as winding down the window or turning up the radio.
Physiological signs of drowsiness:  
  • Feeling sleepy
  • Frequent blinking, or heavy eyelids, and slow blinking
  • Slowing of brain activity
  • Eyes closing or going out of focus
  • Rubbing your eyes
  • Yawning may increase
  • Feeling restless
  • Trouble keeping your head up or head nodding is a sign of severe drowsiness
  • The tendency to doze off when not active for a while; for example, when watching television or waiting in your car at a stop light.

Q: How can I achieve a good night's sleep?

A: Good sleep  practices include7:

  • Maintaining a regular bedtime and wake time.
  • If you cannot fall asleep, do not stay in bed. Try getting out of bed and reading a book or having a light snack. This avoids creating an association between the bed and being unable to fall asleep.
  • Allow time to wind down before bed and avoid activities that demand high levels of concentration shortly before bed.
  • Avoid coffee, alcohol, and nicotine in the hours leading up to bed time. These substances are all stimulants and can disrupt the body's natural sleep rhythm.
  • Avoid daytime napping, or keep to a minimum when sleep is disrupted.
  • Do not stay in bed once you have awoken.
  • Do not schedule exercise too close to bedtime.
  • Avoid use of the bed for non-sleep-related activities (e.g. television watching, reading, studying)
  • Avoid the use of electronics in bed (e.g. phone, tablets, and laptops). As the circadian system is particularly sensitive to light-emitting devices such as iPhones and iPads, these should be avoided prior to bedtime.
  • Ensure the bed and bedroom are conducive to sleep, including dim lighting, temperature not too hot or cold, limited noise and free from stimulating technologies.

Q: Does a 15 minute powernap work?

A: A 'Power nap' is a short nap between 15 – 30 minutes that is aimed at reducing sleep pressure. The nap can be taking after inadequate sleep in order to improve performance ("compensatory" nap) or it can be taken prior to shift work in anticipation of a long period of wake ("prophylactic" nap). For compensatory naps, studies have found that naps as short as 10 minutes can improve alertness temporarily8. Determining the best duration for a nap is complex. This is because, on the one hand, increased sleep will result in greater recovery. On the other hand, longer naps typically result in more of the deeper stages of sleep which may cause individuals to feel groggy and experience diminished performance upon awakening. This experience is known as sleep inertia and can last between a few minutes to hours. Hence, drivers should be wary of driving immediately following longer naps.


1.  SOURCE: http://healthysleep.med.harvard.edu/healthy/science 

2.   SOURCE: Van Dongen HPA, Maislin G, Mullington JM, Dinges DF. The cumulative cost of additional wakefulness: Dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. SLEEP 2003;26:117-26.

3. SOURCE: Dijk DJ, Czeisler CA. Paradoxical timing of the circadian rhythm of sleep propensity serves to consolidate sleep and wakefulness in humans. Neuroscience Letters. 1994; 166 (1): 63-8

4. SOURCE: http://healthysleep.med.harvard.edu/healthy/science

5. SOURCES: http://drowsydriving.org/about/warning-signs/, http://healthysleep.med.harvard.edu and http://www.sleephealthfoundation.org.au

6. SOURCE: www.sleepfoundation.org

7. SOURCE:  http://healthysleep.med.harvard.edu and http://www.sleephealthfoundation.org.au

8. Ficca G, Axelsson J, Mollicone DJ, Muto V, Vitiello MV. Naps, cognition and performance. Sleep Med Rev. 2010 Aug; 14 (4): 249-58.


Case Number 102 - based on real cases analysed

Name: Angela
Age: 35 years old
Sex: Female
Status: Married
Speed zone: 60km/h
Date of incident: 5 March 2012
Time of incident: 5.33pm

Injuries sustained:

  • contusions to the right chest
  • contusions to lower abdomen
  • laceration on right cheek
  • abrasions to right knee,
  • sprained left elbow
  • thoracic spine tenderness


Angela, a 35 year old female, was travelling along on a 60km/h suburban street in the late afternoon. Angela reported feelings of drowsiness approximately 15mins into her 35 minute journey home from work. She was kept awake by her 3 year old son the night before and had a disrupted night's sleep. She thought she could push through the drowsiness and keep herself awake by winding down the window for some fresh air and singing along to the songs on the radio. She has driven while drowsy before and has managed to get home safely – she thought she could do it again. The next thing Angela remembers is waking up to the sounds of sirens and people asking if she is ok.

Angela had fallen asleep at the wheel and her car veered off the road to the right into a telegraph pole. She sustained a number of injuries but fortunately, none of them life threatening but serious enough to keep her from work and attending to her son for a while. This incident could have just as easily ended in tragedy. If this incident happened in a higher speed zone or if she was driving a car without safety features such as airbags, this case study could have had a very different ending.

The fact is you can't fight sleep. The only effective remedy against drowsiness is sleep. So get a good night's rest before any drive, long or short. If you are already on the road and you feel drowsy, make sure you pull over safely and have a 15 minute powernap – it could save your life.