Юго-Западный коридор Бостона: история и перспективы развития транспортной сети.

Former elevated railroad in Boston, Massachusetts
From 1979 to 1987, the four track railroad embankment between Back Bay and Forest Hills, originally acquired for a cancelled highway project, was converted to a trench with three mainline tracks and two rapid transit tracks as the Southwest Corridor project. Addition of rapid transit to the corridor had been proposed as a branch of the predecessor BERy's streetcar network in 1926, and as a relocation of the Orange Line since 1966. The last service over the Washington Street Elevated ran on April 30, 1987; service began over the Southwest Corridor route on May 4. The closing of the Washington Street Elevated prompted a 2012 review, the Roxbury Dorchester Mattapan Transit Needs Study, recommended for some form of proposed replacement rail service to access southern Metro Boston neighborhoods one option being studied within this review would re use the Tremont Street subway's now unused southern Pleasant Street tunnel coming from the Green Line's Boylston station. The new light rail service proposed in the 2012 review, to replace the rapid transit access the elevated previously provided, could go as far south as the Red Line's Mattapan station (via Nubian station), with a northern turnaround terminus at Government Center.

Since the Southwest Corridor was located somewhat further to the west than the elevated had been, away from neighborhood centers like Dudley and Egleston Squares, the MBTA promised that a branch of the light rail Green Line would be built to provide continued rapid transit service to those areas. However, such service was not forthcoming; instead, the 49 Northampton – Washington & Kneeland feeder bus route was extended to Dudley Square and given a more direct routing. The Silver Line has also been subject to neighborhood criticism, as it makes fewer stops than the 49, but nevertheless fails to sufficiently decrease travel times as compared to the previous conventional bus service. The 2003 Program for Mass Transportation considered the possibility of converting the Washington Street section of the Silver Line to light rail, as had originally been promised, by using the abandoned Pleasant Street incline and the currently unused southern segment of the Tremont Street subway to connect with the Green Line at station. However, the Phase III tunnel and continued bus service was recommended instead. In 2012, the aforementioned Roxbury Dorcester Mattapan Transit Needs Study recommended, as a long term project, the light rail conversion of the Silver Line's Washington Street section and its connection to the Green Line via the abandoned tunnel with a northern terminus/turnaround for the new line at Government Center; with the additional possibility of extending the line down Blue Hill Avenue to station (and thus connecting with the Ashmont–Mattapan High Speed Line, and, indirectly, with the Red Line), following the route currently taken by the #28 bus.