(AP) - Amtrak's Northeast Corridor trains will resume service Monday in "complete compliance" with federal safety orders following last week's deadly derailment, officials announced Sunday.

Company president Joseph Boardman said Amtrak staff and crew have been working "around the clock" to restore service along the route between Washington and Boston following Tuesday night's crash that killed eight people and injured more than 200 others.

"Our infrastructure repairs have been made with the utmost care and emphasis on infrastructure integrity including complete compliance with Federal Railroad Administration directives," Boardman said in a statement Sunday.

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

Service along the corridor will resume with departures from New York City at 5:30 a.m. Monday and Philadelphia at 5:53 a.m. Monday, and all Acela Express, Northeast Regional and other services will resume for the first time since the accident, the company said.

Investigators with the National Transportation Safety Board, meanwhile, have focused on the acceleration of the train as it approached the curve, finally reaching 106 mph as it entered the 50-mph stretch north of central Philadelphia, and only managing to slow down slightly before the crash.

"The only way that an operable train can accelerate would be if the engineer pushed the throttle forward. And ... the event recorder does record throttle movement. We will be looking at that to see if that corresponds to the increase in the speed of the train," board member Robert Sumwalt told CNN's "State of the Union."

The Amtrak engineer, who was among those injured in the crash, has told authorities that he does not recall anything in the few minutes before it happened.

Investigators have also been looking into reports that the windshield of the train may have been struck by some sort of object, but Sumwalt said on CBS's "Face the Nation" program on Sunday that he wanted to "downplay" the idea that damage to the windshield might have come from someone firing a shot at the train.

"I've seen the fracture pattern; it looks like something about the size of a grapefruit, if you will, and it did not even penetrate the entire windshield," Sumwalt said.

Officials said an assistant conductor on the derailed train said she heard the Amtrak engineer talking with a regional train engineer and both said their trains had been hit by objects. But Sumwalt said the regional train engineer recalls no such conversation, and investigators had listened to the dispatch tape and heard no communications from the Amtrak engineer to the dispatch center to say that something had struck the train.

"But, nevertheless, we do have this mark on the windshield of the Amtrak train, so we certainly want to trace that lead down," he told CNN.

Sumwalt acknowledged, however, in an interview on Fox News Sunday that train engines are routinely struck by various projectiles without catastrophic consequences.

Sumwalt said the agency had long called for inward-facing video cameras on trains which he said would help provide crucial information about such crashes. And he said the kind of next-generation speed control systems that Congress has ordered installed by the end of the year could have prevented countless accidents over the years. The systems use transponders, wireless radio and computers to prevent trains from going over the speed limit.

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