Driving while tired can be equally as dangerous as drink driving, according to research by consumer magazine What Car?.

Tests conducted in simulators at the Transport Research Laboratory compared the ability of a tired driver with a drunk driver.

In the tests, Driver 1 was not allowed to sleep until 3am and Driver 2 consumed 12 units of alcohol over the course of a night. Both then negotiated a simulator route that included motorways and A-roads.

When 25% over the legal limit, the drunk driver's ability to hold a steady distance from a car in front dropped by 25%, while his ability to keep to the centre of a lane dropped 23%. At 2am, the sleep-deprived driver was 39% less able to maintain a steady distance from a car in front, and his capacity to drive within a lane suffered by 37%.

The drink driver still proved to be the worse driver overall, when twice over the legal limit he was 49% worse at maintaining a steady distance and 42% worse at keeping to his lane. His morning-after results were poor. After eight hours sleep his skills were way below par. He was 26% worse at holding a steady distance from the car in front and 18% less able to keep a straight-line position, and he almost crashed.

The tests show that the dangers of driving whilst tired can become a very real threat. In a whatcar.com poll, 40% of readers admitted to falling asleep at the wheel, and 22% more than once.

Steve Fowler, What Car? Group Editor, said: "It's not surprising to learn that drink seriously affects driving ability, but it is worrying to discover that a sober persons driving ability can suffer more when they are tired.

"Our message to drivers is simple: don't drink and drive and don't drive tired. If you are feeling drowsy, pull over in a safe location, lock the doors and have a nap - better to arrive late than not at all."

While these findings warn of the dangers of driving whilst tired, it begs the question: will this stop people taking to the road when deprived of sleep? The penalties for drink driving have become an established deterrent from driving for those over the limit.

However, it is very difficult to impose a penalty against people who drive when tired, even if they are at times equally likely to cause an accident because of impaired concentration.

What Car? suggests these top tips to stay alert and safe:

• Plan for a good nights sleep if you have a long journey ahead of you. Try to get a little extra shut-eye the night before, and don't take stimulants like caffeine before you head off to bed.
• Don't drive through the night even if you slept well the previous night, fatigue will inevitably set in during the early hours and have an adverse effect on your driving.
• Don't be fooled into thinking that turning down the air-conditioning, opening the windows or playing loud music will help to keep you awake - it won't.
• Plan regular breaks - stop at least once every two hours for a good 20 minutes. Much less than this and you won't feel the benefit.
• If you feel sleepy, find a safe place and stop, lock your doors and take a 20-minute nap. Then when you wake up drink some coffee, or other caffeine-based drink.