(Reuters) — Canada's two big railroads are set to strengthen their safety measures following the deadly train crash on July 6 that killed some 50 people and destroyed the center of a small Quebec town.

Canadian Pacific Railway Ltd., Canada's No. 2 operator, said on Thursday it has already made some changes to its operating rules. These include a ban on parking unattended trains that contain hazardous materials on main lines and tougher rules on setting the brakes that hold a stationary train in place.

The runaway crude-oil train that smashed into Lac-Megantic, Quebec, had been parked on a main line after the engineer, its only crew member, finished his shift. The train, operated by the small Montreal Maine & Atlantic Railway, rolled down the track, derailed in the center of the lakeside town, and exploded.

Investigators say how the train's crucial hand brakes were set is a focus of their probe.

"The recent situation gave us a chance to thoroughly review our safety procedures, as we do on an ongoing basis," CP Rail spokesman Ed Greenberg said in a statement.

"We have now strengthened our operating procedures in some key areas that were identified from what recently occurred."

Canadian National Railway Co., the country's biggest railroad, has also started reviewing its policy for securing trains to strengthen its safety protocols, spokesman Mark Hallman said.

CP said it will now lock the locomotives of trains left unattended outside a terminal or yard. That policy was already in place in certain locations, but will now be extended across the company's network.

Canada's Globe and Mail newspaper said CP was changing its policies in anticipation of new safety orders expected from the federal transportation department, Transport Canada. Transport Canada officials were not immediately available to comment.

Investigators are painstakingly sifting through the Lac-Megantic crash site to determine the cause of the calamity and recover the remains of those who died.

The crash was North America's deadliest rail accident in more than 20 years.