The dangers of sleep debt when driving

Sleep debt, the cumulative effect of insufficient sleep, is a silent but serious threat to road safety. Some people believe that sleep works like a bank where you can store it, therefore catching up on sleep one night will mean that one won’t need as much on another.

However, sleep is actually like a battery. No matter how long you let it charge, once it’s full you cannot expand its capacity.

Whether you’re a long-haul truck driver, busy parent, or a P-plater, if you drive in any capacity, understanding the dangers of sleep debt and how to identify its signs, could save your life. 

With driver fatigue contributing to 20% of road fatalities¹ in Australia each year, it’s vital to stay alert behind the wheel. Knowing how to recognise the warning signs of sleep deprivation can be the difference between arriving safely or not at all.

At Road Sense Australia, we deliver a range of safe driving programs to help road users reach their destinations unharmed. In this post, we’ll explore what sleep debt is, how it affects your driving ability, and practical tips to reduce your risk of fatigue-related accidents. 

What is sleep debt?

Sleep debt refers to the cumulative effect of consistently getting less sleep than your body needs². Put simply, it’s the difference between the hours of sleep you need (about 8 hours) and the amount of sleep you actually get. 

When you don’t get enough rest night after night, your body and brain begin to operate in a state of fatigue, which can impair focus, decision-making, and reflexes³—cognitive and motor functions that are crucial for safe driving.

The warning signs of this fatigue are⁴:

• Constant yawning
• Slow eye movement or constant blinking
• Head snapping/nodding
• Unintentional lane swerving and/or variations in driving speed
• Daydreaming
• Microsleeps – brief and unintended episodes of sleep

Let’s look at some of these warning signs in more detail.

1. Yawning

Yawning is often the first sign that your body is tired⁵. It’s an automatic response when your brain isn’t getting enough oxygen, which happens as you become fatigued⁶. Though it may seem like a harmless reflex, frequent yawning is a clear indicator that your focus and alertness are diminishing—both of which are crucial when driving.

2. Drooping eyelids

When your eyelids begin to feel heavy, it means your body is trying to fall asleep⁶. Continuing to drive under these conditions puts you at a much higher risk of falling asleep at the wheel, which can lead to devastating consequences.

3. Difficulty concentrating

If you find yourself unable to concentrate on the road, missing exits, or failing to notice road signs, it’s a warning that your cognitive abilities are compromised. Reduced concentration can lead to dangerous mistakes and slow reactions, making driving in this state extremely risky.

4. Microsleeps

Microsleeps are brief, involuntary episodes of sleep that last only a few seconds⁶. Although these sleep episodes are short, they are incredibly dangerous when driving, as even a momentary loss of consciousness can lead to serious accidents. If you find yourself experiencing microsleeps, it’s vital to stop driving immediately.

How much sleep should you get before driving?

For safe driving, adults should aim for 7–8 hours of quality sleep before getting behind the wheel. This amount ensures you’re rested, alert, and capable of reacting quickly on the road. Teenagers and young adults may require 8–10 hours⁷, as their bodies and brains are still developing, making them more vulnerable to the effects of sleep deprivation.

Different demographics need varying amounts of sleep to ensure optimal performance. Shift workers or those with irregular sleep schedules should strive to get as much rest as possible, even if it means napping during the day to make up for lost sleep. Older adults may require slightly less sleep, but the quality of rest is equally important for maintaining safety on the road.

What causes sleep debt?

Busy lifestyles

One of the most common causes of sleep debt is a demanding lifestyle. Juggling work, family, and social obligations can often lead people to sacrifice sleep. Over time, these late nights add up, leading to chronic sleep deprivation, which can have serious consequences for drivers.

Irregular sleep patterns

People who work irregular hours or night shifts are particularly prone to sleep debt⁸. Their natural sleep-wake cycle, known as the circadian rhythm, becomes disrupted, making it harder to get consistent, restful sleep. This leads to accumulated fatigue and, ultimately, an increased risk of driving accidents.

Sleep disorders

Sleep disorders such as insomnia, sleep apnea, and restless leg syndrome can prevent individuals from getting sufficient, quality sleep. While sufferers may not realise the extent of their sleep debt, these conditions can lead to serious cognitive impairments, especially when driving.

Consequences of sleep debt for road users

When we have a sleep debt, our tendency to fall asleep the next day increases. The larger the sleep debt or the longer it accumulates, the stronger the tendency to fall asleep – including when you are driving.

Fatigue-related crashes are a leading cause of road fatalities (read more in our blog here), with approximately 20% of all fatal accidents in Australia linked to driver fatigue. 

Driving fatigue heightens the level of risk because a person who is drowsy or asleep cannot effectively react to their surroundings, amplifying the potential severity of a crash.

This doesn’t just affect drivers—pedestrians and cyclists are also at risk. Fatigued drivers are less likely to notice people crossing streets, cycling on the side of the road, or reacting appropriately in high-traffic areas. These dangerous conditions can result in devastating accidents, especially in poor visibility or during long, monotonous drives.

Can you recover from sleep debt?

Yes, it is possible to recover from sleep debt, but it requires consistent effort. 

By gradually increasing your sleep time each night, you can begin to replenish your body’s energy levels and cognitive functioning. However, recovery is not immediate; it may take several days or even weeks of extra rest to fully overcome chronic sleep debt.

Recent research2 suggests that individuals who lost five hours of sleep during the week but tried to make up for it with additional sleep over the weekend still experienced negative effects.

To start, try extending your sleep by an additional 30 minutes to an hour each night. You can also incorporate naps during the day to help restore your body’s natural rhythm.

How to avoid the dangers of sleep debt while driving

To help prevent collisions caused by fatigue, remember to:

• Plan your trip in advance, making note of rest stops and the like
• See if there are alternate modes of transport available
• Ensure you’re not using any medication that will make you drowsy, and 
• Get ample and quality sleep before your trip

These simple tips can help keep you safe on the road and reduce the risk of sleep-debt-related incidents.

1. Plan ahead

Planning is key to avoiding sleep debt. Ensure you get sufficient rest before a long trip, and schedule regular breaks throughout your journey to stay alert. Avoid driving during times when you would typically be asleep, and allow time for short naps if you feel fatigued during your trip.

2. Take alternative transport

If you’re too tired to drive, consider alternative transportation options such as public transport, ridesharing, or asking someone else to drive. These choices may seem inconvenient, but they are far safer than driving while fatigued.

3. Use technology

Modern vehicles are equipped with safety features like lane departure warnings and drowsiness detection systems. While these technologies aren’t a replacement for sleep, they can help alert you to the signs of fatigue so you know when to pull over and have a rest.

4. Stop, revive, survive

If you feel exhausted, pull over and take a break. As you’re driving, remember to stop and revive every 1.5 – 2 hours, or when you show any signs of fatigue. Taking a 20-minute power nap can help reduce the effects of fatigue and help you feel refreshed for the remainder of your drive or day (read about The Science behind Power Naps in our blog here).

5. Get enough sleep

There are various short-term ways to help us ‘wake up’ such as drinking caffeine or having a nap, but we can only truly get rid of sleep debt by tackling the issue at its core – having more sleep.

Make it a point to get at least 7–9 hours of rest before driving, particularly if you have a long journey ahead. Don’t rely on caffeine or other stimulants as a substitute for proper sleep—they might temporarily mask fatigue but won’t resolve the underlying issue.

Get from A to B safely with a Road Sense Australia driving program

Sleep debt is a very real danger on our roads. Recognising its warning signs and taking proactive steps to reduce its risk can make all the difference to road safety. 

That said, while the ‘solution’ to fatigue is simple, our day-to-day activities often get in the way of getting some much-deserved rest. 

At Road Sense Australia, we’re here to help you drive as safely as possible. To learn more about how you can protect yourself and others on the road, discover our Drive It Home and Driver Education programs. 

References

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 

Brossoit RM, Crain TL, Leslie JJ, Hammer LB, Truxillo DM, Bodner TE. The effects of sleep on workplace cognitive failure and safety. J Occup Health Psychol. 2019 Aug;24(4):411-422. doi: 10.1037/ocp0000139. Epub 2018 Nov 29. PMID: 30489101; PMCID: PMC9036851.

Depner et al., 2019, Current Biology 29, 957–967. March 18, 2019 ª 2019 Elsevier Ltd. https://doi.org/10.1016/j.cub.2019.01.069