The rash of exploding railcars across North America was treated with a dash of regulatory tonic this week.

Citing an “imminent hazard” of explosion and fire posed by trains hauling crude, the U.S. Department of Transportation issued an emergency order requiring more thorough testing of oil before it’s shipped. The department is especially concerned about oil from the Bakken shale formation in North Dakota and Montana, as it’s been found to be particularly explosive. The order also bars shipping oil in weak railcars designed for less hazardous materials.

The move could slow train shipments of oil from the Bakken shale and from Canada’s tar sands. Bloomberg reports: