An increase in the number of crashes caused by driver fatigue has Calgary police worried.

Police say there have been 96 collisions involving drivers who nodded off at the wheel so far this year in Calgary.

That's an increase of about one-third from last year's total of 64 – and police say it's likely linked to people pushing themselves harder during the workweek.

"People that are trying to get to their family after a long work week, on the weekend, are driving while they are tired instead of giving themselves some rest," said Sgt. Mike ter Kuile with the Calgary Police Service.

"They want to compact as much into that weekend as possible and they're cutting corners — one of them is sleep."

According to Transport Canada, roughly 20 per cent of fatal car crashes in Canada are caused by driver fatigue.

The problem can be made worse during times when the body's circadian rhythm is thrown out of whack, such as at the beginning or end of daylight savings time. 

"If you don't feel fully awake, don't take a chance," said Adam Moscovitch, a sleep medicine specialist in Calgary. "Don't get behind the wheel of a car because literally it doesn't take more than those two to three seconds and you might end up in a ditch or much worse."

Moscovitch says 15 to 20 per cent of Canadians are chronically sleep-deprived, and that getting at least seven hours of sleep each night is especially important before hitting the road.