Many motorists are driving when tired, with some not stopping at all on long journeys, according to a survey.
More than half (55%) ignore basic advice to take rest breaks at least every two hours on long trips, the poll by road safety charity Brake and insurance company Direct Line showed.
In addition, 9% do not have any breaks on long journeys unless they absolutely have to.
The survey of 1,000 UK drivers also found:
:: 14% of male drivers have driven for six hours or more without stopping, compared with 3% of female drivers;
:: Half of male motorists have driven for four hours or more without stopping, compared with 31% of females;
:: 35% of drivers admit sometimes or always trying to push on if they feel sleepy at the wheel.
Brake deputy chief executive Julie Townsend said: "A large proportion of the driving public are scarily confident they can push on through on long drives without stopping.
"In reality, regular breaks - at least every two hours - are essential for staying alert and awake, as is getting plenty of sleep the night before.
"Sleepiness can catch you unawares at the wheel and it only takes a couple of seconds on a motorway to cause absolute carnage. "
Rob Miles, head of the motor section at Direct Line, said: "Tiredness and driving are a deadly combination.
"Not only is there a risk of falling asleep at the wheel, but when we are tired our reactions and awareness of our surroundings are not as sharp as they would normally be."
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RAC Foundation director Professor Stephen Glaister said: "Officially, fatigue is reported as a factor in just 2% of all accidents but the best estimates are that the real figure is 10 times greater.
"Not only that, tiredness-related crashes tend to be more severe as drivers are unable to take evasive action.
"There is a strong argument for introducing more rest areas on motorways as are common on the continent.
"These are not full-blown service areas but frequent points where people can simply pull in and take a break."