Three days after a train derailment in downtown Philadelphia left a load of crude oil dangling over a river, the National Transportation Safety Board on Thursday recommended strict new safety measures for transporting crude oil by rail.

The NTSB recommendations to the Transportation Department grew out of earlier accidents — notably the  disaster last July in Lac Megantic, Canada, when an unattended 74-car train derailed after a downhill run into town, killing 47 after an explosion and fire.

Some of the six train cars that derailed in Philadelphia on a bridge over the Schuylkill on Monday carried the same type of crude oil that exploded in Lac Megantic. There were no injuries and no oil spilled, but the incident above a river and a major expressway, and close to three hospitals and the University of Pennsylvania, renewed questions about the safety of hauling such material through populated areas.

The Association of American Railroad’s Annual Report of Hazardous Materials says crude oil shipments by rail have increased by more than 400 percent since 2005 .

“The large-scale shipment of crude oil by rail simply didn’t exist 10 years ago, and our safety regulations need to catch up with this new reality,” said NTSB Chairman Deborah A.P. Hersman. “While this energy boom is good for business, the people and the environment along rail corridors must be protected from harm.”

The NTSB, an independent federal agency that must rely on Congress and the Transportation Department to implement its recommendations, issued three recommendations to the Federal Railroad Administration and the Pipeline and Hazardous Materials Safety Administration (PHMSA).

The first would require expanded hazardous materials route planning for railroads to avoid populated and other sensitive areas. The second is for the establishment of an audit program to ensure rail companies transporting petroleum have response capabilities to handle worst-case accidents. The third recommendation is to ensure that hazardous materials are being properly classified and rail carriers have adequate safety and security plans in place.

“If unit trains of flammable liquids are going to be part of our nation’s energy future, we need to make sure the hazardous materials classification is accurate, the route is well planned and the tank cars are as robust as possible,” Hersman said.

Accidents involving flammable liquids that the NTSB  has investigated include a Dec. 30 derailment in Casselton, N.D., and a June 2009, derailment in Cherry Valley, Ill. After the 2009 accident, the NTSB issued several safety recommendations to PHMSA that included making tank cars more puncture resistant and requiring that bottom outlet valves remain closed during accidents. The agency began the rule-making process but has not issued any new rules.

The recommendations that came out Thursday were issued jointly by the NTSB and the Transportation Safety Board of Canada because railroads operate crude oil trains across the U.S-Canada border.