WASHINGTON (REUTERS) - US regulators have ordered passenger railroad Amtrak to immediately take actions to improve the safety of its heavily travelled Northeast Corridor route following Tuesday's derailment in Philadelphia that killed eight people, the Federal Railroad Administration (FRA) said on Saturday.

"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," Transportation Secretary Anthony Foxx said in the news release.

The FRA ordered Amtrak to ensure that an automatic speed control system is in use on northbound trains on the corridor, which stretches 730km from Washington to Boston.

The system, called Automatic Train Control, is in use on southbound trains near the derailment site, FRA said.

The train that derailed was traveling northbound at twice the 80kmh speed limit as it entered a curve and left the track.

ATC detects when a train is travelling above the speed limit, sending a signal to the engineer. If the engineer fails to act to slow the train, ATC will automatically apply the train's brakes.

The Amtrak engineer who was driving the train has told investigators that he has no memory of anything that happened shortly before the wreck, said Robert Sumwalt of the National Transportation Safety Board, which is investigating the accident.

Sumwalt said the Amtrak train and a separate commuter train in the vicinity may have been hit by projectiles of some kind shortly before the accident.

FRA also ordered the railroad to assess the risk on curves on the Northeast Corridor track and make sure technology intended to prevent derailments is in place where the approach speed is significantly higher than the curve speed.

In addition, Amtrak must increase its signage along the track that alerts engineers and conductors to the maximum speed.

Amtrak did not immediately respond to a request for comment.