Drivers carrying ‘sleep debt’ face higher accident risk, study finds

Poor and inconsistent sleep may be one of the biggest hidden threats to road safety, with new research suggesting it is a stronger predictor of vehicle accidents than many traditional insurance risk factors.

Discovery Insure analysed four years of sleep, driving and accident data from more than 10,000 South African drivers and found that chronic sleep deprivation or “sleep debt” accumulated over several nights, substantially increases the risk of being involved in a crash.

The research was presented at a Discovery Insure media briefing in Johannesburg on Tuesday.

The insurer said the findings make sleep one of the most significant, yet often overlooked, contributors to road accidents.

“Our research suggests that poor sleep is up to five times more predictive of motor vehicle accident risk than traditional insurance risk factors considered in isolation,” said Discovery Insure CEO Robert Attwell.

He said inadequate sleep affects concentration, reaction time and decision-making, all of which are critical for safe driving.

The research found nearly 30% of the drivers studied accumulated some level of sleep debt while driving. It also found drivers who maintained less than one hour of sleep debt over three consecutive nights had up to a 36% lower accident risk than those carrying five or more hours of sleep debt over the same period.

Regular sleep patterns also appeared to reduce crash risk. Drivers who consistently slept between seven and eight hours a night were about 32% less likely to be involved in an accident than those who slept too little, while those who went to bed at roughly the same time each night had up to a 36% lower risk of a crash.

The study further found that drivers who obtained sufficient Rapid Eye Movement sleep experienced about a 14% lower accident risk.

The findings come amid growing concern about fatigue behind the wheel.

Discovery cited research showing that remaining awake for more than 16 hours can impair driving to a level comparable with being at or above SA’s legal alcohol limit.

A 2024 survey also found that while almost 90% of adults said they would avoid driving after drinking alcohol, only half said they would avoid driving after a poor night’s sleep.

Globally, road traffic crashes claim about 1.19-million lives every year, with driver fatigue estimated to contribute to one in five road accidents. In South Africa, road crashes cost the economy an estimated R205bn in 2023, equivalent to about 2.7% of GDP.

Attwell said public awareness campaigns have traditionally focused on speeding, distracted driving and alcohol, but the research suggests fatigue deserves equal attention.

Following the findings, Discovery Insure has introduced sleep-based incentives through its Vitality Drive programme to encourage healthier sleeping habits among participating drivers.

The insurer said clients who activate their Vitality Sleep Score and track their sleep using a compatible wearable device can earn additional Vitality Drive points for maintaining consistent sleep patterns. Attwell said the initiative is intended to encourage healthier sleep habits as part of broader efforts to improve road safety.

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