Do you know the signs of being too sleepy to drive?

Drivers with tired eyes are three times more likely to cross the centre line, according to QUT research, which has pinpointed four eye symptoms to help drivers recognise the signs they are too sleepy to get behind the wheel.

Dr Ashleigh Filtness, from QUT's Centre for Accident Research & Road Safety - Queensland (CARRS-Q), said a study that tested 10 sleep-related eye symptoms found heavy eyelids, eye strain, difficulty focusing and difficulty keeping eyes open, were linked to sleepiness and impaired driving.

"This finding, published in the Journal of Sleep Research, offers a physical sign to help those behind the wheel identify when they are too sleepy to drive," she said.

Dr Filtness said the next step in her research was to investigate the on-road experiences of young drivers to find out what factors lead people to get behind the wheel when they are tired.

"We are looking for young drivers who have experienced one or more of these sleep-related signs - heavy eyelids, eye strain, difficulty focusing and difficulty keeping eyes open - but have still driven, to take part in this new study," she said.

"Driver sleepiness or fatigue is one of the leading factors contributing to road crashes worldwide and in Australia it contributes to 20-30 per cent of all crashes.

"Current advice is 'if you are sleepy, don't drive' but the problem is some people struggle to comprehend the exact nature of their sleepiness and in particular pinpoint the signs of when to pull over."

Dr Filtness said the research measured eye symptoms, subjective sleepiness and the driving performance of 16 people on real roads and in simulated driving conditions in Sweden, who completed 64 drives, averaging 150km each drive.

She said the number of line crossings per kilometre travelled by drivers was recorded to quantify impaired driving.

"The results showed drivers who reported tired eyes on real roads crossed the centre line on average once every 14km, compared to those who reported not having tired eyes crossing once every 45km," she said.

"In the simulator tests, drivers experiencing tired eyes crossed on average once every 9km, compared to those who did not have tired eyes crossing once every 111km.

"We found drivers who experience one or more of the four eye symptoms linked to sleepiness are likely to report requiring greater effort to remain awake and be more likely to have unintentional line crossings - a sign of sleep-related driving impairment.

"Eye symptoms that are related to subjective sleepiness (heavy eyelids, eye strain, difficulty focusing and difficulty keeping eyes open) can be used to help drivers identify signs of sleepiness."

To take part in the new online study, drivers must be aged 30 or younger, hold a provisional or open licence and drive at least three journeys per week.