Back Bay to Forest Hills

From the passenger station with  two side platforms beneath an air-rights building above, with the two side platforms of the Orange Line alongside to the north,  at Back Bay (MP 227.6), in the "tunnel" formed by the air-rights construction overhead, the Amtrak line swings south-southwest, CETC, 25 kV overhead electrification, with speed limit 30 mph, past MP 227.0, where the speed limits rise to 100 mph for passenger trains and 45 mph for freights, in a trench with many road bridges overhead where there are gaps in the air-rights construction, the MBTA passenger station at Ruggles Street (MP 226.5), continuing in a trench with many segments of "tunnel" formed by air-rights construction, with an MBTA line running to the west, past crossovers at Plains (MP 224.3), where freight speeds drop to 20 mph, the MBTA passenger station with platforms on all tracks at Forest Hills  (MP 223.7), "tunnel", a road bridge overhead, and the junction at Forest (MP 223.5), where freight speed revert to 45 mph, the Main Line turns south and the Needham Branch turns away southwest.