Three out of 10 (30%) crashes on motorways and major A-roads involving a drowsy driver result in at least one fatality or serious injury, according to new research.
Only accidents featuring drugged drivers or drivers using a mobile phone are more likely to cause a death or serious injury, at 40% and 39% respectively, the AA Charitable Trust said.
Collisions involving drowsy drivers can have particularly severe consequences as there is often no attempt to slow down before it occurs.
The analysis of casualty figures for roads maintained by Highways England in 2017 found that fatigue was the most common driver impairment contributing to collisions resulting in casualties, with 22 deaths and 132 serious injuries.
AA Charitable Trust director Edmund King said: “Drowsy driving is the hidden killer on our roads and, due to it being under-reported, the true picture is estimated to be even worse than these figures show.
“Our own research has shown one in eight drivers admit to falling asleep when driving.
“Falling asleep at the wheel, even for just a few seconds, is incredibly dangerous. Crashes involving a drowsy driver tend to be catastrophic because a driver who is asleep does not brake or steer away from anything.
“Awareness of the dangers is key to start solving the problem. Put simply, drivers need to wake up to the dangers that drowsy driving poses.”
The Trust warned that winding down a window or turning up a radio are not effective remedies for tiredness.
It advised motorists doing these things to stop at the next safe place, drink two cups of coffee – or an equivalent caffeinated drink – and take a 15-minute nap.