The “drunk” effect of poor sleep on driving
How did you sleep last night – and the night before that? When was the last time you woke up feeling rested? Here’s a wake-up call: Driving while sleep deprived can be as dangerous as driving drunk.
Global research shows that being awake for 24 hours can impair driving ability as much as a blood alcohol level of 0.10% – roughly four or five glasses of wine, or double South Africa’s legal limit.
Sleep directly affects cognitive functions such as alertness, attention, decision-making, and reaction time, all of which are critical for safe driving.
But while 90% of surveyed adults were likely to avoid driving after a few drinks, only 50% said they would do the same when they hadn’t had enough sleep, highlighting the need for greater awareness of the dangers of drowsy driving.
Building on this, Discovery’s groundbreaking study, The Sleep Factor, offers one of the most comprehensive analyses of how sleep impacts overall health and driving ability.
The research analysed over 47 million sleep records from 105,000 members of Discovery Vitality over six years.
This data was overlaid with telematics data from over 10,000 Discovery Insure clients who tracked their sleep over four years. The analysis found that:
- Sleep is a 5x stronger predictor of motor-vehicle accident risk than typical risk factors such as demographics
- Drivers who go to sleep around the same time every night reduce their risk of getting into an accident by up to 36%
- Getting enough hours of sleep reduces accident risk by up to 32%, while getting enough REM sleep (deep or quality sleep) reduces accident risk by up to 14%
- Nearly 30% of South African drivers are driving with some level of sleep debt (getting inadequate sleep over multiple days)
These findings support external research that shows that drivers with less than four hours of sleep are 11.5 times more likely to be involved in an accident than those who slept for seven hours.
“Sleep is absolutely critical,” says Discovery Insure CEO Robert Attwell. “We spend – or should spend – a third of our lives sleeping, yet we tend to underestimate the importance of sleep. “
“The reality is that most of us aren’t sleeping as well as we think. This has a major impact on long-term health and driving.”
“We’ve always used technology and behavioural science to help our clients become better drivers,” says Attwell.
“Now we see that better sleep is just as powerful as any driving tip. When people rest well, they drive well, and that’s something the data proves beyond doubt. Even after just one night of poor sleep, we see the effect in how people drive.”
“However, sleep debt, which is multiple nights of poor sleep in a row, is what really drives accident risk.”
How poor sleep shows up behind the wheel
Discovery Insure’s Vitality Drive programme uses telematics devices to monitor real-time driving behaviour, such as braking, speeding, phone use, and general driving style, among other factors.
This feedback is provided to drivers to help them assess their performance and identify areas for improvement. The better you drive, the more Vitality Drive points you earn and the rewards you can receive.
This data, combined with insights from Vitality, gives Discovery Insure unique insights into how sleep patterns affect driver behaviour.
“If you have a few hours of poor quality sleep, your risk of an accident the next day is more than 30% higher than someone who slept well,” Attwell explains.
A 2024 National Sleep Foundation survey found that almost 90% of adults were likely to avoid driving when they’d had a few drinks, but only 50% said they’d do the same when they’d had poor sleep.
The AAA Foundation for Traffic Safety also reports that drivers who get only six to seven hours of sleep are twice as likely to cause an accident, while those with five hours or less are four to five times more likely to crash.
Dr Nadine Rampf, Associate Professor in the Division of Clinical Anatomy at the University of Stellenbosch, explains: “Most adults need between seven and nine hours of sleep for optimal function, yet few of us actually achieve it.”
“Sleep isn’t downtime; it’s active biology, the night programme that keeps the brain and body working.”
“Skip that process or cut it short and – behind the wheel – that means slower reaction times, momentary eye closures (microsleeps), drifting out of lane, failure to brake, and poorer judgment and decision-making.”
Fewer accidents, safer drivers
Fewer accidents mean fewer claims, but Discovery Insure’s purpose goes beyond that. The goal is to encourage safer driving habits through behavioural science, data and technology and, in turn, help create a nation of safer drivers.
“Our goal isn’t just to reduce claims, it’s to create safer roads and healthier people,” says Attwell. “When drivers prioritise sleep, they improve focus, reaction times and judgement – critical factors for avoiding accidents and handling unexpected road conditions.”
Better sleep starts with better habits
Sleep is a behaviour that is largely in your control, and much like exercise and nutrition, it requires discipline and consistency.
You can’t undo one night of bad sleep overnight, but you can make small changes, such as going to bed and waking up at the same time every day, including on weekends, or putting away your devices at least an hour before bedtime.
Here are a few more tried-and-tested tips from experts and health industry professionals to help improve your sleep:
- Avoid exercising and eating after 7pm
- Get natural light early in the day – this helps reset your circadian rhythm, or natural body clock, which signals your body to get up and then go to bed
- Switch your phone and computer to night mode around 6:30 pm to reduce blue-light exposure and help your body produce more melatonin for better sleep
- Watch your caffeine and alcohol before bedtime, as both affect deep sleep
- Aim for 7 to 8 hours of sleep a night
- Keep your bedtime and wake-up times consistent, even on weekends
“Sleep is personal. There is no one-size-fits-all,” says Attwell.
“What matters is awareness. Understand your patterns, know what affects your rest and make small adjustments. Those small wins can make a big difference. Sleep quality depends on three things: consistency, duration, and depth. Get those right, and you’ll not only feel better but also drive better.”
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