TORONTO - If police could lay their hands on a device that would tell them how much sleep drivers had before getting behind the wheel, more than four million Canadians would have reason to worry.

Research shows at least 20 per cent of Canadians - an estimated 4.1 million people - admit to having nodded off at the wheel in the past 12 months.

Since there's no such invention, researchers and policy makers are looking at other ways to help drowsy drivers avoid accidents that kill hundreds of Canadians every year.

"Over 26 per cent of all fatal injury crashes involve fatigue," Mark Yakabuski, vice-president of Insurance Bureau of Canada, told a driver fatigue symposium in Toronto on Wednesday.

"That means that over 180 people are killed on our roads because of fatigue in Ontario alone, and over 400 across Canada every year."

In-vehicle devices to monitor drivers are in the experimental stages. Some are designed to track the head movements while others monitor blinking frequency or pupil size. But there's currently no testing system in place to monitor sleep deprivation behind the wheel.

That means driver fatigue remains much harder to prove than drunk driving, but it can be just as deadly.

Experts say fatigue has the same effect on drivers as alcohol in that it slows reaction time, decreases awareness, impairs judgment and increases the risk of crashes.

Studies suggest that a person who goes without sleep for 17 hours straight will suffer from a level of impairment that is equal to having a blood-alcohol level of .05 per cent.

Those who go 24 hours without sleep show a level of impairment equal to having a blood-alcohol level of .1 per cent - slightly higher than the legal limit.

"Unrecognized medical factors," and not just a lack of sleep, can contribute to driver fatigue as well, said Dr. Henry Moller of University of Toronto.

More evidence-based research is needed to allow scientists to better understand the nature of drowsy and fatigued driving, said Moller.

Fatigued drivers are a danger to themselves and to everyone else on the road, Ontario Minister of Transportation Donna Cansfield told the conference.

Driving safe "is a personal requirement, a personal responsibility and a personal obligation because driving in this province is a privilege, not a right," she said.

The provincial government is changing the law so that truck, bus and school bus drivers have enough rest before they show up for work. The government is limited in what it can do to enforce the same rules on private drivers.

Building shoulder edges and centre-line rumble strips, keeping road-side test stops operational year round and raising public awareness are among steps being taken by the province to combat the problem, said Cansfield.

"There's no such a thing as an accident," she said. "It's totally, absolutely and completely preventable."

The fact that the government wants drivers to have more sleep, be well-rested and not work long shifts does little to prevent some Toronto cab drivers from working long hours behind the wheel.

"I started working at 7 a.m. this morning," said Ali, a taxi driver who did not want his surname used.

"It's 1 p.m. and I have only made $50, so I have to work at least until 7 p.m. to cover my daily car expenses and take some money home."

When business is good, Ali said, some drivers go up to 20 hours without sleep.