Commuter rail What is now the surface section of the D branch was formerly the
Highland branch of the
Boston and Albany Railroad (B&A). The portion between
Brookline Junction and was built by B&A predecessor
Boston and Worcester Railroad in 1848. The
Charles River Branch Railroad extended the line to
Newton Upper Falls in 1852, and later to
Woonsocket, Rhode Island. Passenger service on the 1852-built line south of Cook Street ended in 1927. (A portion in Needham remains in use as part of the
Needham Line).
Conversion to light rail Conversion of the Highland branch to a third-rail rapid transit line was proposed in 1913. That proposal called for trains to reach downtown Boston using the then-under-construction
Boylston Street subway, which was built for streetcars but sized for rapid transit conversion, with a connection near
Governor Square. The plan, released in 1926, called for the existing streetcar subway to be converted into two rapid transit lines. A number of potential future extensions were listed; among them was conversion of most of the Highland branch to rapid transit, linking with a
Huntington Avenue subway at Brookline Village. In 1943, the state legislature appointed a commission headed by
Arthur W. Coolidge to plan for the future of transit in the Boston region. In 1945, a preliminary report from the Coolidge Commission recommended nine suburban rapid transit extensions – most similar to the 1926 plan – along existing railroad lines. The Highland branch was to be converted to a rapid transit line, using low-floor trains that could operate in the existing streetcar subway. A branch would use the former Charles River Branch Railroad route to . Separately, two tracks of the B&A mainline would be converted to rapid transit, also terminating at Riverside. The project was approved by the MTA Advisory Board on October 1, 1957, and the state Department of Public Utilities on December 6. The
Interstate Commerce Commission gave a certificate of abandonment early in 1958. The B&A ran its last passenger trains on the branch on May 31, 1958. The MTA acquired the line from the B&A at a cost of $600,000 (equivalent to $ million in ) on June 24. Work began with a groundbreaking ceremony on July 10, 1958. Initial plans called for every other train to short turn at Reservoir. However, the outer section of the line had higher ridership than expected, and soon all trains operated to Riverside. From June 8 to September 11, 1974, buses ran between Kenmore and Reservoir while the inner portion of the line was reconstructed. A temporary loop was used near Reservoir station, allowing D branch trains to use the C branch between Reservoir and Kenmore. (On March 5, 1974, the downtown terminal had been cut back from Lechmere to North Station to accommodate the longer running times associated with this rerouting.) Weekend D branch service was extended to Lechmere on March 28, 1997; weekday service followed on June 21. It was cut back to Government Center on June 19, 2004, to accommodate the demolition of the
Causeway Street elevated and the opening of the new underground North Station. Green Line service to Lechmere resumed on November 12, 2005, though the D branch continued to terminate at Government Center. The
National Transportation Safety Board investigation concluded that the operator likely had an episode of
micro-sleep caused by
sleep apnea. On October 25, 2010, the MBTA began operating some three-car trains on the D branch at peak hours. This was expanded on March 21, 2011, but was discontinued on March 21, 2016, in favor of operating two-car trains on more consistent headways. The Fenway Portal project was completed on November 23, 2020. The track and signal work was completed in December 2021. Three nine-day closures of the whole D branch took place between September 24 and October 28, 2022, to allow for work including installation of a train protection system and track replacement between Eliot and Riverside. , the MBTA plans to use a section of the D Branch between Chestnut Hill and Newton Centre for the testing of new
Type 10 vehicles until 2032. Two crossovers will be installed to allow
single-track operation on a section of the westbound track. The eastbound track will be used as a test track.
Accessibility Riverside station was rebuilt in the late 1990s, with raised platforms to provide accessible boarding on the Type 8 light rail vehicles then being built. Reservoir and Brookline Village were temporarily fitted with portable lifts for accessibility, with Brookline Hills added by 2003. Newton Centre, Reservoir, and Fenway were retrofitted with raised platforms around 2003. Woodland was rebuilt for accessibility in 2006, followed by Longwood and Brookline Village in 2009. Reconstruction of Brookline Hills station took place from September 2019 to January 2022 as part of the construction of an expansion of
Brookline High School. Temporary work to make accessible was done in 2019–2020. Design work for a full reconstruction was completed in 2023. Design work for the remaining four non-accessible stops (Beaconsfield, Chestnut Hill, Eliot, and Waban) was completed in late 2022. They were made "generally accessible" with work done in October 2024. Full reconstructions of the four stations to serve
new Type 10 vehicles are planned to begin in 2026, followed by Newton Highlands in 2027.
Green Line Extension Original plans for the
Green Line Extension called for the D branch to be extended through the rebuilt
Lechmere station to
Medford/Tufts station, with several intermediate stops. However, in April 2021, the MBTA indicated that the D branch would instead be extended to , with the
E branch running to Medford/Tufts. The D and E branches were chosen for the extension because they serve the
Longwood Medical Area; the D branch was assigned to the shorter Union Square Branch because its western leg is longer than that of the E branch. The Union Square Branch opened on March 21, 2022. It was initially served by the E branch rather than the D branch. The western portion of the E branch was closed from August 6–20, 2022, for track work; during that time, Union Square was served by C branch trains plus Reservoir short turns from the D branch. Upon reopening, most D branch service (plus E branch service) began running to Union Square, though some peak hour trains short turned at Government Center. E branch trains began non-revenue test service to Medford/Tufts on November 1, 2022, leaving only the D branch serving Union Square. The closure was originally planned for July 18 to August 28, but was delayed and shortened due to public criticism. ==Station listing==