Every day, hundreds of thousands of cars travel on Canada's busiest highway, the 401 that runs from Windsor to the Quebec border. And at one spot, over 80 per cent of them were going at illegal speeds.

Ontario has some of the slowest highway speed limits in the world, but few people are actually obeying them, data from a CBC Marketplace investigation reveals.

Over the course of a single day at one location Marketplace monitored, dozens of cars were barrelling along at speeds so dangerous that the drivers would immediately face licence suspension if caught.

Out of 45,133 cars tracked near Toronto, only 17 per cent were driving at or below the speed limit.

Ontario has some of the slowest highway speed limits in the world, but few people are obeying them. (CBC)

"If you have that percentage and those numbers driving in excess there's something very wrong" with the speed limit, says Martin Parker, a traffic engineer who regularly consults on highway speed limits in North America.

"Most of us try to obey the law. It's just simply when we find the law is not appropriate for the conditions that it gets violated, and obviously here it gets violated on a daily basis."

The Marketplace investigation on speed limits and safety airs Friday, Oct. 30 at 8 p.m. (8:30 p.m. in Newfoundland and Labrador) on TV and online.

Do you think Canada should have #FasterLimits or #SlowerLimits? Take a side now.

So how fast are we going?

To find out how effective current speed limits are, Marketplace tracked drivers on the Macdonald–Cartier Freeway, better known as the 401, with test methods used by the Ontario Ministry of Transportation.

Marketplace collected speed data for three days near Oshawa and Bowmanville, just east of Toronto.

Looking at data from a single day — Tuesday, Sept. 1 — at eastbound traffic near Bowmanville, provides an interesting picture of what daily drivers face.

On this day, this location was free of serious accidents, so the data gives a clear picture of how drivers behave when traffic is moving under normal conditions.

Dangerous speeds

Of the 83 per cent of drivers who were speeding, many were not even close to the speed limit of 100 km/h. Almost 10,000 cars, 22 per cent of all the drivers on the road that day, were travelling at least 20 km/h above the limit.

Marketplace also found that 33 drivers were going at dangerously fast speeds: at least 150 km/h.

“Most of us try to obey the law," says Martin Parker, a traffic engineer who regularly consults on highway speed limits in North America. "Obviously here it gets violated on a daily basis.” (CBC)

If the rules were enforced, these drivers would have their cars impounded by police. Seven cars were travelling at 160 km/h or faster.

In Ontario, drivers going more than 50 km/h above the speed limit immediately lose their car and licence for seven days, and are subject to a fine of up to $10,000.

"The risk of a fatality or serious injury is almost five times greater for vehicles crashing at 50 km/h or more above the posted limit on a highway with a posted limit of 100 km/h," says the website for the Ontario Ministry of Transportation.

The fastest time of day

While the period between 3 and 4 p.m. was the busiest time on the road, with the most cars competing for space, according to the data, drivers were more likely to speed later in the day.

Between 6 and 8 p.m., one-third of all drivers were doing at least 120 km/h.

Experts agree that the faster a car is going, the more dangerous accidents can be.