The Federal Railroad Administration ordered Amtrak Saturday to make changes to improve train safety along the Northeast Corridor. Above, National Transportation Safety Board officials on the scene of Amtrak Train No. 188, which derailed Tuesday in Philadelphia, killing eight and injuring hundreds, in this handout photo provided by the board, May 13, 2015. Reuters/National Transportation Safety Board/Handout

The Federal Railroad Administration ordered Amtrak to make changes along the Northeast Corridor to improve safety and prevent crashes, the administration said Saturday. It issued its instructions four days after an Amtrak train derailed around a bend in the tracks in Philadelphia, killing eight and injuring more than 200 people.

Amtrak needs to ensure its Automatic Train Control system, which automatically slows trains traveling above the speed limit, was being used in both directions along the stretch of tracks that runs from Boston through New York City to Washington, passing through Philadelphia and Baltimore along the way. The administration noted Automatic Train Control was currently being used for southbound trains along the corridor, but not for northbound ones, including the train bound for New York City from Washington that crashed Tuesday night.

The administration also ordered Amtrak to reassess speed limits in the Northeast Corridor and increase the number of signs posting those limits. "Amtrak must also take a new look at all curves along the corridor and determine if more can be done to improve safety in any of these areas," it said, instructing the train company in particular to re-examine current speed limits before and along all curves in the track.

"The actions we have instructed Amtrak to take are aimed at improving safety on this corridor immediately, but we won't hesitate to require the railroad to do more to improve safety as the accident's causes become clearer," U.S. Transportation Secretary Anthony Foxx said in a statement.

Amtrak would have to report back to the railroad administration regarding the orders issued Saturday, but it was not clear by when. The administration said the instructions would be made into a formal emergency order in the coming days.

After Northeast Regional Train No. 188 derailed around a sharp bend in the tracks in Philadelphia Tuesday night, investigators found the train had been hurtling into the curve at 106 mph, more than twice the speed limit of 50 mph.