More than three million British drivers have fallen asleep behind the wheel in the last year, according to new research.
Almost one in 10 (3.4 million) of the UK's more than 38 million motorists "nodded off" while driving, found a survey for LV= car insurance firm.
It contributed to at least 3,357 fatigue-related accidents which have been recorded over the past five years, according to official police figures obtained by the company.
Among the main causes were long and monotonous roads, a lack of sleep, driving long distances to a holiday destination or after a late work shift.
A fifth (19%) of those surveyed confessed they had hardly been able to keep their eyes open while driving and close to a third (28%) had driven while drowsy.
Men (33%) were more likely to be affected by the problem than women (12%).
And with drivers covering an average distance of 26 metres (85 feet) at an average speed of 50mph when they dozed behind the wheel, sleeping motorists were estimated to have done a total of more than 55,000 miles in the last 12 months.
John O'Roarke, managing director of LV= car insurance, said: "Falling asleep while driving, even momentarily, is extremely dangerous but taking regular breaks from driving can help prevent it.
"If you know you are going to be driving long distance, plan ahead and make sure you have sufficient time to rest."