Train service resumed on the Ashmont branch of the Red Line Friday at around 9:30 p.m., the MBTA tweeted.
Passengers were put on shuttle buses earlier after a power problem had delayed service, the MBTA tweeted.
Moderate delays had been reported between Ashmont and the JFK/UMass stops, the agency said around 7:30 p.m.
The source of the power problem was not disclosed.
An MBTA spokesman did not immediately respond to a request for comment Friday night.Alana Levene can be reached at firstname.lastname@example.org. Follow her on Twitter @alanalevene.