Bruce Crummy/Associated Press

Near Casselton, N.D., on Monday, a train carrying crude oil crashed into a train carrying grain that had derailed.

WASHINGTON — Safety officials have worried for years about hazardous materials carried on trains, but concern has intensified recently as a drilling surge in remote oil fields has generated heavy traffic on North America's aging rail-freight networks.

That concern was heightened on Monday when a train of oil-tank cars near Casselton, N.D., plowed into a train carrying grain that had derailed on an adjacent track. The fire burned for more than a day.

That accident was outside the town. But last July, in Lac-Mégantic, Quebec, a similar train of tank cars that had been left unattended rolled down a grade and derailed, killing 47 people and burning down much of the downtown.

Even before the accident in Quebec, the United States Transportation Department had warned that shippers were failing to follow basic precautions, like determining the temperature at which oil will turn into a gas and burn or explode, and selecting appropriate tank cars to transport the material.

On Thursday, the department told oil shippers and railroads that it was "imperative" to test the oil being transported to determine its volatility. The department is also considering stricter requirements for the tank cars themselves, which are prone to puncture and burn in derailments. Sometimes the problem is as basic as the effect of a derailment, which can throw open valves and spill flammable contents.

Tank car specifications pit the shippers, which own the rail cars, against the railroads, which say they do no more than haul the cars. The National Transportation Safety Board recently called the level of threat to the public "unacceptable." Municipal officials are worried.

"We have a couple of sets of tracks that run through town and we can see the increased number of cars going through," said Jeff Lawler, the village manager of Barrington, Ill., about 30 miles northwest of Chicago. Barrington was among several local governments to ask the Transportation Department to put tighter controls on shipments of dangerous chemicals, including oil.

"These tank cars, they've known for 20 years, they have failed in different derailments," Mr. Lawler said. "It's not like that's new news." But "just looking at the math, with the increases, the likelihood of tragedies occurring here or elsewhere increases," he said.

Deborah A. P. Hersman, the chairwoman of the safety board, said in a telephone interview, "It's called 'hazardous material' for a reason."

Derailed grain trains attract wild animals to feed at the site, creating another hazard. If the train carries coal, "it's not a big deal, you pick it up and drop it back in the hopper and move on," she said. But with oil, "we want to make sure we're addressing it in a way that's commensurate with the risk." And risk rises with traffic, she said.

The cargo involved in Monday's accident was crude oil from the Bakken formation in North Dakota. The state's oil production has doubled in the last two years and will nearly double again in the next three, to 1.6 million barrels a day, according to the state Department of Mineral Resources in Bismarck. Rail shipment capacity has increased far faster than pipeline capacity.

The safety board cited national figures that show that in 2012, there were 37 times the number of crude oil shipments by railroad as there were in 2007. Ethanol shipments more than quadrupled between 2005 and 2011, according to the board.

In February 2003, in Tamaroa, Ill., a train carrying methanol derailed and forced the evacuation of 850 people in a three-mile radius. In 2006, in New Brighton, Pa., a train carrying ethanol derailed, and the resulting fire burned for 48 hours. The Federal Railway Administration has been trying to persuade shippers to sample and characterize their shipments so they would be put in appropriate tank cars, although investigators have not said if that was a factor in Casselton.

The railroad industry voluntarily adopted new standards for newly built tank cars, although these are not as strict as the safety board recommends. A spokeswoman for the Association of American Railroads, Holly Arthur, said that about 14,000 of the 98,000 tank cars in service met the standard. Her group favors replacing the old cars, not retrofitting them, she said.

The safety board has pointed out that if a train uses a mix of new and old designs, the benefit of the new designs will be lost if an older car derails, ignites and sets off the others.

Opponents of tighter standards argue that weak or defective tank cars do not cause derailments. But safety officials say that derailments happen daily.

In the next two years, railroads are supposed to install "positive train control," using GPS technology, which could alert engineers to problems ahead — as millions of car drivers are alerted — and could prevent some crashes.

The safety of rail shipments also affects the arguments over the Keystone XL pipeline, which would carry oil from Alberta to the Gulf Coast. While opponents of the pipeline claim that exploitation of the oil sands creates too much carbon dioxide, they have lately focused on pipeline leaks and spills. But few of those cause catastrophic fires.