Shuttle buses have temporarily replaced Red Line service on the MBTA between the North Quincy and JFK/UMass stations due to a power problem, according to MBTA officials.
Customers are being encouraged to use the Commuter Rail from Braintree and Quincy Center to South Station.
Authorities said a track maintenance vehicle derailed earlier this morning on the southbound side which caused the delays. That equipment has been removed but MBTA crews are still on the scene working.
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Service is expected to resume at about 6 a.m.