WASHINGTON (AP) — Fiery wrecks of trains hauling crude oil have intensified pressure on the Obama administration to approve tougher standards for railroads and tank cars despite industry complaints that it could cost billions and slow freight deliveries.

On Feb. 5, the Transportation Department sent the White House draft rules that would require oil trains to use stronger tank cars and make other safety improvements.

Nine days later a 100-car train hauling crude oil and petroleum distillates derailed and caught fire in a remote part of Ontario, Canada. Less than 48 hours later, a 109-car oil train derailed and caught fire in West Virginia, leaking oil into a Kanawha River tributary and burning a house to its foundation. As the fire spread across 19 of the cars, a nearby resident said the explosions sounded like an "atomic bomb." Both fires burned for nearly a week.

The two accidents follow a spate of other fiery oil train derailments in the U.S. and Canada over the past few years. The most serious killed 47 people and destroyed the town center of Lac Megantic in Quebec, Canada, just across the border from Maine, in 2013.

The government hasn't yet unveiled its proposed regulations. But among them are a stronger tank car design that includes thicker tank walls and electronically-controlled brakes that stop rail cars at the same time rather than sequentially, said Brigham McCown, a Washington-based consultant who was head of the federal agency responsible for safe transportation of hazardous materials during President George W. Bush's administration.

Typically, safety regulators propose tough regulations and the Office of Management and Budget, which looks at economic and other implications of the rules, demands they be scaled back. This time, however, there may be less resistance.

"The more incidents we have, the less likely the administration will be willing to listen to industry," McCown said. "I think the railroad industry starts to lose credibility every time there is an accident."

Kevin Book, an energy industry analyst, said it has become harder to imagine the administration accommodating the industry.

The oil and rail industries want thinner tank walls — half an inch thick, instead of the 9/16ths-inch that regulators propose. The thicker the shell, the less oil a tank car can hold, and with about a half-million carloads of crude hauled by rail in the U.S. and Canada last year, the cost difference could add up.

The tank cars in the recent accidents were built to a voluntary standard written by industry in 2011 to answer criticism that cars used to transport flammable liquids were prone to rupture in an accident and spill their contents and ignite spectacular fires. But the two most recent accidents show that the newer cars — known as 1232s — also are prone to rupture, even at slow speeds. Both trains were traveling under 40 mph.

"Those folks who were arguing that the 1232s may in fact be puncture-proof really can't make that argument anymore," Sen. Heidi Heitkamp, D-N.D., told reporters.

A Transportation Department analysis predicts that trains hauling crude oil or ethanol will derail an average of 10 times a year over the next two decades, causing more than $4 billion in damage and possibly killing hundreds of people if an accident happens in a densely populated part of the U.S.

Chris Hart, the acting chairman of the National Transportation Safety Board, urged federal regulators in a blog post this week to act swiftly to set new tank car standards, noting that while the government deliberates over new rules, more 1232 cars are entering service.

Industry officials say they need every car they can get to meet shipping demands, and it will take time for manufacturers to retool for a new design. U.S. and Canadian officials also have not agreed on a phase-out period for the train cars that regularly cross their border.

Transportation Secretary Anthony Foxx told The Associated Press that administration officials understand the gravity of the issue and are committed to a "comprehensive approach" that includes better braking and slower train speeds, as well as enhancing the ability of fire departments to respond to accidents.

Railroads complain that electronically-controlled brakes would cost them $12 billion to $21 billion and that lower train speeds would back up other rail traffic through much of the country, slowing freight deliveries and passenger service. Last year they agreed to reduce oil train speeds to 40 mph in high-population areas. Regulators have discussed turning that voluntary limit into a requirement.

But former NTSB Chairman Jim Hall said that until safety is improved, oil trains shouldn't be allowed to travel any faster than the typical school bus — about 25 mph.

___

Online:

Pipeline and Hazardous Materials Safety Administration http://www.phmsa.dot.gov/

___

Follow Joan Lowy on Twitter at http://www.twitter.com/AP_Joan_Lowy