How fatigue, sleepiness and tiredness increase your vehicle accident risk

We usually associate tired driving with driving at night but fatigued driving can happen any time of the day in response to how we have slept before that moment. Sleep interruption can have anything from almost no effect to a severe effect on our cognition of driving. One study in Australia said that after being awake 17-19 hours we drive with the equivalent of 0.05% blood alcohol content and when we have been awake 24 hours or more, this increases to 0.1% which is over the legal limit.

There are times of the day where you are more likely to fall asleep at the wheel – 2-4pm and 1-6am. Everyone has a circadian rhythm that controls this. They also have a homeostatic rhythm which governs the internal drive to go to sleep. Even when you are not naturally sleepy there are things that cause sleepiness. There are also a number of actions and activities that stave off sleep temporarily, but they can’t stop it forever.

How to stop yourself falling asleep at the wheel

Note that each of the following might only be effective for a matter of minutes and, depending on how tired you are might not be effective at all. The only way to stop yourself falling asleep at the wheel is to stop and have a nap. However, if you’re in a place you can’t stop, or you’re just a few minutes from your destination, some techniques will give you that amount of time.

1. Chemical stimulation

We self-medicate with caffeine, energy drinks and other drugs like cocaine or modafinil. These can be very effective for short periods of time but come with the risk of long-term abuse and any side-effects. They also cost money and, in some cases, are illegal. Sugary energy drinks tend to produce a burst of alertness followed by a sugar crash.

2. Mental stimulation

Talking to a passenger, listening to a podcast, singing along to the radio, commentary drives and other ways of engaging our brain can give you a vital few more minutes before fatigue sets in, particularly if the road you are driving on is a boring, straight motorway with light traffic.

3. Physical stimulation

Pinching yourself, chewing gum, moving in your seat and shaking your head are ways people try to stave off the urge to sleep. The effects of physical stimulation don’t last long and they don’t change the underlying requirement for you to go to sleep.

How can you tell you are driving tired?

Once you feel a desperate need to go to sleep while driving, you’ve let it go too far. There are many signs you can heed before this happens:

Your eyes

• Increased blinking rate
• Blurry vision (difficulty keeping focus)
• Rubbing your eyes

Your body and mind

• Feeling irritable
• Yawning
• Changing posture frequently
• Nodding head
• Concentration lapses

Your driving

• Late braking in response to hazards, e.g. cars braking ahead of you
• Difficulty keeping your vehicle in one lane, e.g. drifting from side to side
• Difficulty maintaining a constant speed
• Missing hazards completely
• Missing signs, directions, exits and turn-offs

Microsleeps

If you wait too long you will start having microsleeps where your eyes might remain open but your brain goes to sleep for up to a few seconds. These get longer and longer until you either have a crash or you actually fall asleep.

How many accidents are caused by lack of sleep?

At least 20% of road accidents have sleep deprivation or fatigue as a major cause, with around 30% of single-vehicle rural crashes thought to be caused by fatigue. Figures are fairly consistent between developed countries.

What technologies will reduce sleep-related accidents?

It’s very common for people to be sleep-deprived, more so than, say, 50 years ago when our bright computer screens didn’t keep us awake at night and obesity-related sleep apnoea wasn’t as prevalent. Vehicle technology is assisting people to avoid sleep-related accidents.

• Forward collision warning is an audible and tactile warning that warns drivers that they are at risk of having an accident unless they brake.
• Autonomous emergency braking does the braking for you if you’re about to crash.
• Lane keep assist stops you drifting so much in your lane.
• Drowsiness detection systems are provided in some Audi and Mercedes-Benz models, and it’s becoming more common in trucks and other commercial vehicles.
• Fully autonomous vehicles will prevent sleep-related accidents completely.