Drivers have been warned to take rest breaks

Brake spoke to 1,000 drivers and said 45% had put lives at risk by doing so, with 10% "tired driving" once a month.

The survey was released as a government campaign warning drivers of the dangers of tiredness was relaunched.

Brake said 20% of crashes on monotonous roads such as motorways were caused by tired drivers and urged ministers to introduce measures to cut the problem.

'Lethal combination'

Chief executive Mary Williams said: "The results are extremely disturbing.

"Drivers need to wake up to the fact that tiredness and driving are a potentially lethal combination.

Tired drivers are just as impaired as if they were well over the legal drink-drive alcohol limit Professor Jim Horne

"If you risk getting behind the wheel not having had enough sleep you risk killing yourself and other innocent road users."

Crashes involving tired driving tended to be worse because drivers did not brake before the collision, the charity said.

Loughborough University Sleep Research Centre said its studies showed that drivers who had had five hours' sleep had only a one in ten chance of staying fully awake on a lengthy journey.

Professor Jim Horne said: "If these drivers realised that by driving while tired they are just as impaired as if they were well over the legal drink-drive alcohol limit, then they might have second thoughts."

Driver Gary Hart fell asleep at the wheel causing the Selby crash

Government Campaign

The government is now relaunching its "Think Don't Drive Tired" campaign, first unveiled shortly after driver Gary Hart was jailed for five years for causing the deaths of 10 people in the Selby rail crash.

A jury decided that Hart fell asleep at the wheel of his Land Rover in February 2001 before it plunged off the M62 into the path of an oncoming train.

Mary Dunn, the widow of the train's driver Steve Dunn, told GMTV: "The problem is lack of sleep is not as measurable as alcohol is, but they have now proved that driving without sleep is equivalent to being over the legal limit for alcohol."

She said people tended not to take the issue so seriously because it was more difficult to prove.

The government advises drivers to plan a 15-minute break every two hours of their journey in which they should drink a caffeinated drink and have a nap.

But Brake wants the government to do more and is calling for year-round "tired driving" ad campaigns, continuous modern crash barriers on motorways and a review of the frequency of motorway service stations.