The state’s congressional leaders are pushing federal authorities to require rail shippers to correct design flaws in oil tankers that exploded in a Quebec town on July 6, killing 47 people, they said Wednesday.

U.S. Reps. Mike Michaud and Chellie Pingree encouraged Pipeline and Hazardous Materials Safety Administration chief Cynthia Quarterman during a meeting Wednesday to authorize improvements to the 40,000 flawed DOT-111 tanker cars in service now.

“It is still too early in the investigation to determine exactly how this tragedy could have been prevented, [but] the design flaws of DOT-111 tank cars are well documented,” Michaud and Pingree said in a joint statement, calling the rulemaking process “frustratingly slow.”

“We need to avoid any further delays, especially given the exponential growth of hazardous material shipments. Whether it’s oil, ethanol, or some other hazardous material travelling on our nation’s tracks, the American people deserve to know that these shipments are being carried in tanker cars that are designed to the highest safety standards,” they said.

The safety administration announced Monday that it needs another year to apply recommendations from the National Transportation Safety Board that would fix flaws, first discovered in 1991, that cause the DOT-111 rail car to crack open during collisions and derailments.

The runaway Montreal, Maine and Atlantic Railway train that exploded in Lac-Megantic had 72 DOT-111 cars carrying light crude oil. Several cars cracked open and exploded when the train derailed.

The disaster has forced the closure of the track line, the layoff of at least 85 railway workers, and safety reviews in Canada and the U.S.

The safety board’s recommendation came after an accident in which a Canadian National Railway Co. freight train traveling 36 mph derailed at a rail grade crossing in Cherry Valley, Ill., in June 2009.

Thirteen of 19 tank cars carrying denatured fuel ethanol, a flammable liquid, caught fire, killing one nearby motorist, injuring seven others and doing $7.9 million in damage, according to the National Transportation Safety Board report on the accident.

The report lists five accidents or studies involving the DOT-111 tank cars, which are unpressurized, dating to May 1991 in which investigators found tank head and shell breaches, damaged valves and fittings, or both.

“This represents an overall failure rate of 87 percent and illustrates the continued inability of DOT-111 tank cars to withstand the forces of accidents, even when the train is traveling at 36 mph, as was the case in this accident,” the report on the 2009 incident states.

Quarterman had no public response to the meeting with Michaud and Pingree, but her agency and the Federal Rail Administration announced Tuesday that they will review

federal regulations regarding rail transport of hazardous materials Aug. 27-28 in Washington, D.C.