Amtrak has resumed service on the Northeast corridor, almost a week after a deadly crash in Philadelphia claimed the lives of eight people and injured more than 200 others.

Investigators are still trying to determine the cause of the derailment, FOX News reported.

The first train left New York at 5:30 a.m. ET, whereas the first northbound train, expected to depart Philadelphia at 5:53 a.m, was delayed and left the station at 6:07 a.m. Services between NYC and Philadelphia, one of the busiest passenger rail corridors, were suspended since the accident that took place on Tuesday night.

Amtrak President and CEO Joseph Boardman said in a statement on Sunday that the safety of the passengers and the crew was the company's "number one priority."

"Our infrastructure repairs have been made with the utmost care and emphasis on infrastructure integrity including complete compliance with Federal Railroad Administration directives. Amtrak staff and crew have been working around the clock to repair the infrastructure necessary to restore service for all the passengers who travel along the Northeast Corridor," he added, according to USA Today.

Federal regulators on Saturday have directed Amtrak to install the automatic train control system, which monitors and controls the speed of the vehicle, before they resume services on the northeast corridor where the derailment took place.

According to Federal Railroad Administration spokesperson Kevin Thompson's announcement on Sunday, the new technology is now completely functional on the northbound corridor. Trains traveling through those tracks will be monitored by the system, alarming engineers to reduce speeds when their trains are travelling too fast and automatically applies the brakes if the train continues to accelerate.

The agency has also issued orders to Amtrak to inspect all curves along the Northeast tracks to see if anything else can be done to improve safety, and install more speed limit signs along the route.