U.S. transportation officials pressed for companies Thursday to develop safer ways to transport oil on the nation’s rail lines after some explosive accidents as crude trains proliferate across North America.After a closed-door meeting with oil and railroad executives in Washington, D.C., Transportation Secretary Anthony Foxx said the industry agreed to make voluntary changes aimed at accident prevention within 30 days. Topping the list are plans to analyze the risks of oil trains that have begun regularly passing through major metropolitan areas across the U.S., Foxx said. The results could be used to alter some routes, government officials said. Railroads will also consider where oil trains could be slowed down to lessen the potential danger in areas that pose the greatest threat to public safety. “The industry, if they are motivated, can undertake preventive steps that will enhance the safety of the movement of these materials across the country,” Foxx said. The Obama administration faces increased pressure to act after fiery accidents over the past seven months in North Dakota, Quebec, Alabama and New Brunswick. But a safety advocate said the proposed measures fail to address a crucial and long-standing problem: defects in many of the tank cars used to haul crude.“Just moving the problem around is not solving it,” said Karen Darch, president of the village of Barrington, Ill., and co-chairwoman of a coalition of local officials who have pushed for rail safety enhancements. “If you did that, you are creating too high a risk for the area where [oil trains] might be rerouted.” The accidents have revealed significant gaps in federal oversight of the rail industry, and emergency officials in cities and towns across the U.S. have said they would be ill-prepared to handle another derailment. Under current rules, shipments of most hazardous liquids, including oil, do not have to undergo the type of risk studies that were proposed Thursday. Those studies are limited to a few radioactive, explosive and highly toxic chemicals. The rapid expansion of crude by rail has been fueled by booming U.S. production of shale oil, particularly in the Bakken oil patch of North Dakota and Montana. Trains hauling 3 million gallons of crude per shipment to refineries go through hundreds of towns and dozens of cities, from Chicago and Kansas City to Philadelphia and Seattle. Guidelines issued in August by the Association of American Railroads capped speeds at 50 mph for trains hauling 20 or more tank cars of crude. It’s unclear how the speed reductions proposed Thursday would be different. Experts say the same high-grade qualities that make Bakken oil attractive to companies can also make it prone to ignite during an accident. Railroads recently began pushing for retrofits to improve the safety of 78,000 older, defective tank cars that make up the bulk of traffic hauling oil and other hazardous liquids. Oil companies that own or lease the tank cars have resisted retrofits, which could cost $1 billion.