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There are 5 tracks serving Amtrak and commuter rail service. Tracks 2, 1, and 3 (in order south to north) serve Amtrak's Acela Express and Northeast Regional plus the MBTA's Providence/Stoughton Line, Franklin Line, and Needham Line. Tracks 5 and 7 on the Framingham/Worcester Line and the Lake Shore Limited serve westbound trains from a separate island platform. The Orange Line tracks and platforms lie between these two groups of mainline rail tracks.
Because Amtrak's Downeaster trains traveling northeastward to Portland, Maine do not depart at Back Bay or South Station, travelers that wish to make a connection via subway are advised to disembark at this station and take the Orange Line to North Station, which is where Downeaster service originates.
Read more about this topic: Back Bay (MBTA Station)