Amtrak trains began rolling Monday on America’s busiest passenger rail corridor almost a week after a deadly crash in Philadelphia, where investigators are working to determine the cause of the derailment.

Company President Joseph Boardman said Amtrak staff and crew have been working around the clock to restore service following Tuesday night’s crash that killed eight people and injured more than 200 others.

Federal regulators on Saturday ordered Amtrak to expand use of a speed-control system long in effect for southbound trains near the crash site to northbound trains in the same area.

Federal Railroad Administration spokesman Kevin Thompson said Sunday the automatic train control system is now fully operational on the northbound tracks. Trains going through that section of track will be governed by the system, which alerts drivers to slow down when their trains go too fast and automatically applies the brakes if the train continues to speed.

The agency also ordered Amtrak to examine all curves along the Northeast Corridor and determine if more can be done to improve safety, and to add more speed limit signs along the route.

U.S. Transportation Secretary Anthony Foxx told the 150 people present at Sunday’s service that Amtrak’s action on the ordered changes was one way to honor the eight passengers killed in the crash. Many were riding home to their families, he said.

Almost 20 people injured in the train crash remain in Philadelphia hospitals, five in critical condition. All are expected to survive.

Article by The Associated Press