A mudslide on the Trans-Canada Hwy. near Banff snarled traffic for hours on Friday, July 20, 2012. (LARISSA BARLOW/QMI AGENCY)

CALGARY - The Trans-Canada Hwy. came to a standstill Friday after a mudslide closed the roadway in both directions near Banff.

And by nightfall, only residents of the town or people with hotel or campsite reservations were allowed into Banff while others were turned away at the east gate.

Banff RCMP closed the highway 2 km west of the townsite in Banff National Park about 3:30 p.m. after mud and debris covered all four lanes of the highway, both east and westbound, said Parks Canada spokesman Mark Merchant.

About a metre and a half of mud and debris slid onto the westbound lanes, and a half metre covered the eastbound lanes, he said.

The debris was about 100 metres at the widest end.

Traffic was backed up from the Norquay turnoff to almost out of the park for most of the afternoon and evening.

Parks officials did slope stability tests and at 6:30 p.m., determined it was safe to reopen a single eastbound lane to traffic.

By about 8:15 p.m., Mounties closed the east gate to the park, not allowing any westbound traffic through, and advised drivers to turn around and head to Canmore or Calgary until the slide was cleared.

Only residents of Banff and those who could show proof of a campsite or hotel reservation were permitted through the gate.

And depending on where they were on the highway, anyone stopped on the road between the slide and the gate were turned around with the help of RCMP directing traffic, Merchant said.

“The people on the road, if they are near a turnoff, they are allowing them to turn around if they don’t have a reservation,” Merchant said.

“But some people will be stuck on the road for awhile.”

By press time, RCMP spokeswoman Doris Stapleton said the estimated time of reopening was between midnight and 1 a.m. Saturday.

Hwy. 1A from the east entrance, west to the Johnston Canyon Campground, was also closed.

Merchant said a number of factors contributed to the mudslide.

“We had record snowfall, there is still lots of snow melting, and a wet June and prior to the event, we had a thunderstorm that lasted about 90 minutes,” he said.

Drivers took to Twitter and Facebook to express their frustrations with weekend trips off to a bad start and traffic parked because of the inconvenient act of nature.

“Stuck in the worst traffic jam of all time, all due to a mudslide #damnyoumothernature” said one tweet by a Jerry Zhang of Ontario.

Merchant said he is well aware of the many motorists who are off to the mountains, cottages or B.C. lakes for the weekend.

“What we need right now is patience,” he said.

“Our first priority is safety.”