The Transportation Department issued an emergency order Tuesday requiring stricter standards for shipping oil by rail, a move that follows a series of derailments and growing concerns that crude from the Bakken shale formation is more flammable than most.

The order, which is effective immediately, mandates greater testing of crude oil from the Bakken to ensure it's properly classified before being loaded onto rail cars. It also calls on those who pack crude oil onto rail cars to adhere to the strongest two federal levels, which require a "more robust tank car," according to the DOT.

"In light of continued dangers associated with petroleum crude oil shipments by rail, the actions described in this Order are necessary to eliminate unsafe conditions and practices that create an imminent hazard to public health and safety and the environment," the order said.

A handful of recent derailments — including a July one in Lac-Mégantic, Quebec, that killed 47 people — shed light on some of the logistical issues presented by skyrocketing shipments of crude by rail to accommodate rapid production in the Bakken, the heart of the United States energy boom that rests in North Dakota and Montana. New pipeline additions have failed to keep pace, pushing crude-by-rail shipments 400 percent higher since 2005, according to Transportation.

Lawmakers have called on the department to quicken development of new tanker safety regulations, which are due in 2015. The House Transportation and Infrastructure Committee is holding a hearing Wednesday on crude-by-rail safety, which includes a handful of federal officials as witnesses.

The federal government has been more vocal about the threats posed by crude-by-rail shipments as well. The National Transportation Safety Board recommended new shipping standards last month, as it warned accidents could cause a "major loss of life."