WASHINGTON — The National Transportation Safety Board on Tuesday added railroad tank car upgrades to its list of “Most Wanted” safety improvements, reflecting a heightened awareness about problems in transporting crude oil and ethanol by rail.

It was the first time tank cars have appeared on the board’s annual list of safety priorities since it issued the first one in 1990. The board also renewed its call for railroads to install positive train control, a collision-avoidance system, by the end of the year.

The NTSB makes recommendations but has no power to enforce them. The U.S. Department of Transportation regulates the shipment of hazardous materials by rail and is finishing new standards for tank cars that reflect the NTSB’s recommendations.

But the department won’t have the new tank car standards completed by Thursday’s deadline, set by Congress last month when it passed a $1.1 trillion spending bill. In a report on the department’s significant rules in the making, the tank car measure isn’t scheduled for publication until May 12.

The January deadline was attached to the spending bill by Sens. Patty Murray, D-Wash., and Susan Collins, R-Maine.

In an email Tuesday to McClatchy, Murray said she was “extremely disappointed” that the department will miss the safety rules deadline.

“In communities across Washington state and our entire country, we’ve seen oil train traffic increase exponentially,” she said. “Plain and simple: These trains, which often carry oil in badly outdated tank cars, pose serious safety risks to our communities, and there is no excuse … to delay in issuing new safety standards.”

Starting in 2006, a series of fiery ethanol train derailments showed the car’s vulnerability to damage, including punctures and ruptures, that released flammable materials.

Then in 2013, an oil train derailment in Lac-Megantic, Quebec, killed 47 people and destroyed part of the town. All 72 cars on the Montreal, Maine & Atlantic Railway train were DOT-111 cars, carrying crude oil from the Bakken oil fields of North Dakota to an Irving refinery in St. John, New Brunswick, when the engineer parked it outside of Lac-Megantic for the night. The unattended train’s brakes failed, and the train barreled down eight miles of tracks before derailing in the center of the lakeside tourist town.

The structure of the tank cars was not believed to be a factor in the derailment. But accident investigators said it may have played a role in the explosions and fire that ensued, citing the tank cars’ thin shells, lack of shielding and thermal insulation, and the absence of devices that protect valves from opening unintentionally.

Since then, Maine’s congressional delegation has been pressuring federal agencies to act quickly to improve tank car safety. Meanwhile, Montreal, Maine & Atlantic filed for bankruptcy and eventually was purchased by Fortress Investment Group and renamed Central Maine & Quebec Railway.

The railway’s new president and CEO said in September that he wants to modernize the railroad so it can operate safely and efficiently, carrying lumber and other forest products as its primary cargo. The line still goes through Lac-Megantic and won’t carry oil through the town until at least 2016, he said.

The NTSB has not taken a position on an appropriate deadline for replacing or upgrading the DOT-111 fleet. The Transportation Department proposed a two-year phase-out of the oldest cars for the most hazardous materials, beginning in October.

Industry groups would like more time to make the changes. They have said the two-year deadline could create rail car shortages and require that more oil be transported by trucks.

Although it may not have appeared on prior “Most Wanted” lists, the NTSB has recommended tank car improvements for many years. In 1991, it warned that the most common type of tank car, the DOT-111, lacked adequate protections in derailments involving hazardous materials.

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