Almost half of all motorists have driven when seriously fatigued, a survey conducted for Green Flag Motoring Assistance has revealed.
It found that 45% of motorists had driven within the past year on less than five hours sleep. It also showed that 10% of divers had done so at least once a month.
Green Flag spokesman Nigel Chatsworth said: "Despite tiredness being a major cause of road deaths, the research shows that a significant number of people still underestimate the dangers.
"We hope these results act as a wakeup call for motorists to realise that getting behind the wheel while tired puts their and other road users' lives at risk, and is just as unacceptable and dangerous as drink or drug driving."
Green Flag said its report was supported by a study at Loughborough University which found that after five hours sleep, drivers had only a 10% chance of staying fully awake for the length of their journey.
