In response to a series of fiery train explosions, U.S. regulators issued crisis rules ordering shippers to conduct extensive tests on crude oil moving by rail. "Today we are raising the bar for shipping crude oil on behalf of the families and communities along rail lines nationwide -- if you intend to move crude oil by rail, then you must test and classify the material appropriately," Transportation Secretary Anthony Foxx said in a statement Tuesday. The emergency order, effective immediately, requires all crude to be classified in one of two higher-risk categories, even if test results indicate it is less dangerous, the Transportation Department said. The American Petroleum Institute, which represented the oil industry in negotiations with the government, had no immediate comment. The trade association hadn't yet provided data the DOT requested to reach a voluntary agreement, the Wall Street Journal said. The order covers crude shipments from anywhere but focuses on oil extracted through hydraulic fracturing from Bakken formation shale in parts of North Dakota, the department said. Production in many booming Bakken oil fields has far outpaced the availability of pipelines in recent years, prompting producers to ship the oil to refineries by railroad. The rules are a response to growing safety concerns stemming from moving Bakken crude by rail, the department said. An unattended 74-car runaway freight train carrying Bakken formation crude derailed in Lac-Megantic, Quebec, near Maine, in July, resulting in a fireball explosion that killed 47 people and destroyed 30 buildings. A November derailment in Pickens County, Ala., led to another explosion of the North Dakota crude. A December explosion in Casselton, N.D., caused the town to be evacuated. Crude from the Bakken formation, which straddles North Dakota and Saskatchewan and Manitoba in Canada, is more volatile than traditional heavy crude, the DOT said after the December explosion. It is also more likely to emit flammable gases, the Journal reported this week. The U.S. rule changes follow a similar move in Canada last fall, Canada's Globe and Mail said.