U.S. Secretary of Transportation Anthony Foxx delivers remarks at the 45th annual Washington Conference on the Americas on "U.S. Policy in the Western Hemisphere" at the State Department in Washington April 21, 2015. REUTERS/Gary Cameron (Gary Cameron/Reuters)

Almost two years after a runaway tank-car train erupted in an explosion that killed 47 people in a Canadian town, the U.S. Transportation Department on Friday announced new standards for tank-car construction, new brake-system requirements and speed limits for trains.

Three tank-car trains have derailed in the United States this year, two of them exploding in flames. With a boom in domestic oil produced in the Bakken oil fields, which straddle the U.S.-Canadian border, the number of rail-car loads carrying the flammable material in the United States has grown from 9,500 seven years ago to 493,126 last year.

The trains make their way from the Bakken fields in North Dakota and Montana to refineries on the East and West coasts, regularly passing through major cities.

“It only takes one accident to create a big problem for a community and a country,” said Transportation Secretary Anthony Foxx, flanked by Canada’s minister of transport, Lisa Raitt. “This rule is recognition that we have growing risk.”

He said that by April 2020, all tank cars will be manufactured to new design standards or upgraded to meet them.

“We’re putting brand new tank-car standards in place,” Foxx said Friday. “We’re also requiring retrofitting to bring existing tank cars up to this standard.”

In addition to requiring changes in design that would make tank cars less prone to leaking when trains derail, the new regulations require installation of new braking systems to prevent “accordion-like” pileups in derailments.

The new rule also limits the speeds of trains with 70 or more tank cars to 40 mph in “high-threat” urban areas and requires railroads to take into consideration 27 safety factors — including the quality of track maintenance and the rail bed’s grade and curvature — in selecting routes for tank-car trains.

The major derailments in the United States this year all have occurred in rural settings with few people nearby, but the trains routinely travel through major cities such as Chicago. Those derailments were:

• Feb. 4: Fourteen tank cars carrying ethanol jump the tracks north of Dubuque, Iowa, and three of them burst into flames.

• Feb. 16: Twenty-eight tank cars carrying crude oil derail and catch fire in rural West Virginia.

• March 5: Twenty-one tank cars derail and leak crude oil within yards of a tributary of the Mississippi River in rural Illinois.

Sen. Charles E. Schumer (D-N.Y.), co-sponsor of a pending bill to help communities prepare for potential derailments, said the new regulations were “tough” but should be imposed more quickly.

“The timeline is a little lenient,” Schumer said. “The railroads and the oil companies are in a new world, and they have to adapt to it. They’re making record money because of the oil, and they can put some of that aside for safety.”

Sen. Maria Cantwell (D-Wash.), whose home state is crisscrossed by tank-car trains, was more critical.

“The new DOT rule is just like saying let the oil trains roll,” Cantwell said. “It does nothing to address explosive volatility, very little to reduce the threat of rail-car punctures, and is too slow on the removal of the most dangerous cars.”

Rep. Peter A. DeFazio (D-Ore.), who has pushed for improvements to tank cars, welcomed the action.

“I want to congratulate Secretary Foxx for issuing a final rule on rail tank cars transporting flammable materials, including crude oil and ethanol,” DeFazio said. “The National Transportation Safety Board first recommended replacing and retrofitting these cars more than 20 years ago. At first glance, this rule will provide certainty to manufacturers, shippers and railroads and better protect the American public.”

NTSB Chairman Christopher A. Hart said the rule was “a significant step toward improving the safety of transporting crude oil and ethanol by rail.”

But the American Fuel and Petrochemical Manufacturers, a trade association, said that the “aggressive retrofit schedule is unrealistic and may be disruptive to transporting crude oil to markets across the country.”

“Now that tank-car specifications have been addressed,” the group’s vice president, Brendan Williams, said in a statement, “AFPM suggests that it is long overdue for DOT to show similar concern for the root causes of train derailments: track integrity and human error.”

A spokesman for another industry trade group, the Railway Supply Institute, said the deadline for tank-car makeovers was “aggressive but appropriate.”

“It will be a challenge to meet these obligations,” Tom Simpson, the spokesman, said.