TORONTO — The weak safety culture of a now-defunct railway company and poor government oversight were among the many factors that led to an oil train explosion that killed 47 people in Quebec last year, Canada’s Transportation Safety Board said in a new report released Tuesday.

TSB chair Wendy Tadros said 18 factors played a role, including a rail company that cut corners and a Canadian regulator that didn’t do proper safety audits.

The safety board issued its report 13 months after a runaway train carrying 72 carloads of volatile oil from North Dakota derailed, hurtled down an incline and slammed into downtown Lac-Megantic, Quebec. Several train cars exploded and 40 buildings were leveled. The unattended train had been parked overnight on a rail line before it came loose.

Montreal, Maine &Atlantic Railways went bankrupt after the disaster.

“We now know why the situation developed over time,” Tadros told a news conference in Lac-Megantic. “A weak safety culture at MMA, poor training of employees, tank cars that didn’t offer enough protection.”

The TSB, which is responsible for investigating rail, air and marine accidents, blamed another government agency, Transport Canada, for failing in its oversight duties.

“And then Transport Canada didn’t audit railways often enough and thoroughly enough to know how those companies were really managing, or not managing, risk,” Tadros said.

The safety board said Transport Canada, which is responsible for regulating railways, must ensure railway safety measures are effective. Canadian railways must implement additional physical defenses to prevent runaways, the board said.

Canadian Transport Minister Lisa Raitt said she has directed Transport Canada to quickly develop concrete actions to the TSB recommendations and said the department has acted decisively in moving to implement the TSB’s previous recommendations.

Tadros said Transport Canada knew Montreal, Maine &Atlantic Railways was having problems but proper follow up was not done.

TSB chief operating officer Jean Laporte called Montreal, Maine &Atlantic’s operations “dubious” and said the railway chose to limit the speed on certain routes instead of improving its equipment. “People only did the bare minimum to get the job done rather than always following the rules,” Laporte said.

The safety board said the train’s brakes weren’t properly set by the engineer.

In May, the Montreal, Maine and Atlantic Canada Co. and three of its employees were charged by Quebec prosecutors with 47 counts of criminal negligence causing death. Class-action lawsuits are pending.

The crash, the worst railway accident in Canada in nearly 150 years, prompted intense public pressure to make oil trains safer. Canada’s transport minister said in April that the type of tankers involved in the disaster must be retired or retrofitted within three years because they are prone to rupturing.

The oil industry has rapidly moved to using trains to transport oil in part because of oil booms in North Dakota’s Bakken region and Alberta’s oil sands, and because of a lack of pipelines.

The safety board previously cited easily breached tank cars and highly volatile oil as factors.

The Lac-Megantic disaster along with a string of other explosive accidents across North America prompted the U.S. Department of Transportation to issue an alert about the potential high volatility of crude from the Bakken oil patch. The U.S. agency said that light crude oil from the Bakken oil region, which straddles North Dakota, Saskatchewan and Manitoba, may be different from traditional heavy crudes because it is prone to ignite at a lower temperature.

Edward Burkhardt, the Montreal, Maine and Atlantic Canada chairman who became the target of the community’s anger last year, said he could not comment on the report because of pending legal cases.

John Giles, CEO of Central Maine and Quebec Railway, which purchased the assets of Montreal, Maine and Atlantic Canada, said the first thing he did upon taking over the railroad in May was to shut down operations for two days to talk about safety with employees in the U.S. and in Canada. The railroad now has experienced leadership and management that has been using better safety practices, he said.

Giles said that safety improvements include the elimination of one-man crews, the hiring of a senior superintendent for Canadian operations and the swapping out of old locomotives. The railroad also is spending $8.5 million on overhauling neglected track and will delay any crude oil shipments until 2016, he said.