They completely restore train service on lines 1, 2 and 3 on the Upper West Side after several days of inactivity.
Service was stopped after two trains collided near the 96th Street station Thursday afternoon.
Now, the National Transportation Safety Board is investigating what caused the accident and how to prevent it from happening again.
The MTA says an out-of-service train collided with a 1 train that had more than 200 passengers on board.
Both trains, each with 10 cars, derailed.
The board says the investigation is being conducted because it is the second time in just over a month that an incident has occurred with MTA trains.
In November, a transportation employee died after being hit by a car in Herald Square.
Federal officials say MTA security improvements they recommended in 2015, including inward- and outward-facing cameras and event data recorders, have not yet been implemented.
