WASHINGTON — An emergency order requiring trains hauling crude oil and other flammable liquids to slow down as they pass through urban areas and a series of other steps to improve safety were announced Friday by the Department of Transportation.

The Obama administration has been under intense pressure from members of Congress as well as state and local officials to ensure the safety of oil trains that traverse the country after leaving the Bakken region of North Dakota. To get to refineries on the East and West coasts and the Gulf of Mexico, oil shipments travel through major metropolitan areas such as Philadelphia, Seattle, Chicago, Newark and dozens of other cities.

There have been a series of fiery oil train explosions in the U.S. and Canada in recent years, including one just across the border in Lac-Megantic, Quebec, that killed 47 people.

Major freight railroads have already limited oil trains to no more 40 mph in “high threat” urban areas under a voluntary agreement reached last year with Transportation Secretary Anthony Foxx. But Friday’s order makes the speed limitation a requirement and extends it to trains carrying other flammable liquids like ethanol.

The voluntary agreement also applied only to trains that used older tank cars that are easily ruptured in crashes. The new order includes tank cars constructed since 2011 that were designed to replace the older cars, but which have also repeatedly ruptured in crashes, spilling their contents. So far this year there have been four oil train derailments resulting in huge fireballs — two in the U.S. and two in Canada. All involved the newer tank cars.

The department has also issued an advisory to railroads to strengthen its procedures for checking for flaws in train wheels that can cause a crash. A broken train wheel is suspected of causing the March 5 derailment near Galena, Ill., of a train hauling 103 cars of Bakken crude.

The department also wants inspectors with the highest qualifications to conduct brake and mechanical inspections before trains carrying oil and other hazardous liquids depart.