The department issued an emergency order requiring all companies sending oil from the Bakken region by rail to test and classify it properly.
"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," Department of Transportation Secretary Anthony Foxx said in a statement Tuesday.
The department's Pipeline and Hazardous Materials Safety Administration issued a safety alert in early January saying the type of crude oil in the Bakken reserve area may be more flammable than other grades.
A series of derailments of trains carrying crude oil prompted regulators to look into the transit option. Older DOT-111 cars, some of which were involved in recent derailments, may be more vulnerable to leaks or explosions than other types of rail cars, regulators said.
Industry officials say the increase in U.S. oil production is more than the existing pipeline network can handle, forcing some energy companies to use rail to send crude oil to refineries.