Drivers are being warned to use caution after a fresh dump of snow on top of already ice-covered roads created treacherous conditions and led to hundreds of crashes around Calgary on Friday.

The winter storm left conditions hazardous on routes around southern Alberta, and crashes forced some highways to be closed for a short time.

Police say there were 211 collisions reported on Calgary roads between midnight and 4 p.m. Friday, with 15 resulting in injuries.

This car spun off the road at Parkdale Boulevard and 31st Street N.W. early Friday morning. (Tiphanie Roquette/Radio Canada)

Just after 10 a.m., police tweeted that conditions on Stoney Trail between 17th Avenue and Peigan Trail S.E. are treacherous, with emergency crews responding to five collisions and a jack-knifed tractor trailer.

West of Calgary, the Trans-Canada Highway at the Old Banff Coach Road was impassible for several hours in the eastbound lanes after numerous collisions and vehicles spun out into the ditch, RCMP said in a release.

The route was cleared and open again by 11:45 a.m.

Traffic was backed up much farther than usual and moving at half the normal speed during the Friday morning rush hour heading east into downtown on Bowness Road N.W. (Christine Boyd/CBC)

Airdrie RCMP also sent a release saying there had been numerous weather-related collisions on Highway 2 from north Airdrie south to Calgary city limits. Southbound traffic was reduced to a single lane and northbound lanes were moving very slowly.

The most common mistakes drivers make in snowy conditions are travelling too close and driving too fast, AMA driver education manager Ron Wilson said on CBC's Alberta at Noon.

"On a day like today, it could take up to 12 times longer to stop your vehicle," he said.

"The most important safety feature in your vehicle is your brain."

Winter storm and snowfall warnings issued by Environment Canada on Thursday remain in effect for Calgary and for much of central and southern Alberta.

​About eight centimetres fell at the Calgary airport from midnight to about 11:30 a.m., while areas to the west saw heavier snow, said Environment Canada. The station at Exshaw reported 21 centimetres has accumulated since the snow started Thursday night.

"It's going to be an extended period of snowfall," said Environment Canada meteorologist Brian Proctor.

Calgary is forecast to get 10 to 20 centimetres before the storm slowly pushes to the east late Saturday or early Sunday.

The snowfall record for today's date is 10.2 cm, set in 1939.

Calgary Transit warned riders that several routes might be delayed or on detour. As of 9:10 a.m., Route 93, Route 94 and Route 29 were on detour.

Our crews are working on Priority 1 routes, plowing and laying down gravel and salt for traction. All major roads remain partially snow-covered and slippery. Motorists are advised to take caution and drive to winter conditions. <a href="https://twitter.com/hashtag/yycsnow?src=hash&ref_src=twsrc%5Etfw">#yycsnow</a> —@yyctransport

Good morning <a href="https://twitter.com/hashtag/CTRiders?src=hash&ref_src=twsrc%5Etfw">#CTRiders</a> our snow removal crews are out trying to clear a path for you but we ask that you use extra caution on ramps, stairs, and platforms until we can get caught up. Not a good day to run for the train. —@calgarytransit

"Buses that travel on hills will have challenges today — if your bus stop is on a hill please proceed to either the top or bottom of the hill as a precaution," Calgary Transit said on its website.

A spokesperson for the city's roads department says crews worked through the night clearing snow and extra staff have been recruited for the weekend.

Warnings cover wide swath of province

Winter storm warnings reach as far north as Grande Prairie and Barrhead; east to Red Deer, Lloydminster, and Medicine Hat; south to Brooks and Okotoks; and snowfall warnings to the west for Rocky Mountain House, Kananaskis, and Crowsnest Pass.

Calgarians can expect to be doing a lot of this over the weekend. (Scott Dippel/CBC)

And while it might seem like March is the time winter should be letting up, Proctor points out that spring in Alberta is actually one of the snowiest seasons in this part of the country.

"Our heaviest snowfall events typically occur in March and April and perhaps early May, across the Canadian Foothills or the Rockies," he said.

"So while we want those warmer temperatures, we want to see that spring come, oftentimes it's accompanied by some intermittent, heavy sort of snowfall."