DRIVERS need to be rested properly before setting off on long journeys, says road safety organisation GEM Motoring Assist.

The warning comes as families make plans for getaways that could involve road journeys of several hundred miles.

Being tired when you're driving raises the risk of a collision, because you're less aware of what's happening around you, according to GEM.

A driver's ability to react is compromised if a risky situation develops.

Fatigue is believed to be a factor in up to 20 per cent of all road collisions, and up to 25 per cent of fatal and serious crashes.

GEM road safety adviser James Luckhurst said: "A fatigue-related crash is around 50 per cent more likely to result in death or serious injury, because a driver who has fallen asleep at the wheel will be unable to reduce speed or change direction to avoid a collision.

"The consequences can be devastating."

Falling asleep at the wheel is easily avoided, but as James Luckhurst added, it's vital you heed the many warning signs your body will give you before you actually nod off.

"No one simply falls asleep without passing through various stages of tiredness and distraction - all of them are easy to recognise," he said.

"You will experience difficulty focusing on the driving task, you may fidget, yawn constantly and rub your eyes frequently. When more serious levels of fatigue set in, you may find your thoughts constantly wandering away from driving, you may drift to the left or right, you may be slowing down without realising and you'll suddenly find you cannot recall anything that happened in the past few minutes.

"At this stage your driving performance is seriously impaired, and it's vital that you stop somewhere safe as soon as possible. A power nap and/or a caffeine-based drink can provide a short-term fix, but they should never be used as an acceptable substitute for proper rest.

"If you're that tired, you must stop and rest properly."

GEM offers five tips for drivers to reduce the risk of a fatigue-related collision:

1. Get a good night's sleep before setting out on a long journey.

2. Don't press on into the night. Avoid driving at times when you would usually be asleep.

3. Avoid heavy meals on journeys, especially at lunchtime, as these can increase sleepiness in the afternoon.

4. On long journeys, take a break of at least 15 minutes after every two hours or 100 miles. Get out of the car, do some exercise, stretch or walk. If necessary, have a caffeine drink or two to boost your alertness.

5. You'll know when fatigue is affecting you. It doesn't just take you by surprise. So resist the urge to keep going, and take a proper break.