The B branch, frequently referred to as the Commonwealth Avenue branch or the Boston College branch, constitutes a portion of the MBTAGreen Line light rail network that runs along Commonwealth Avenue to the west of downtown Boston, Massachusetts. As one of the Green Line's four branches, it extends from Boston College station through the median of Commonwealth Avenue until reaching , where it enters the Blandford Street portal and proceeds to Kenmore station. At Kenmore, it converges with the C and D branches, continuing onward via the Boylston Street subway and Tremont Street subway into downtown Boston. Since October 2021, service on the B branch has ended at . Unlike other Green Line branches, this line operates solely within the city limits of Boston. The well-known Green Line Rivalry between Boston College and Boston University takes its name from this branch, which provides transit access to both campuses.
As of , trains run every 8 minutes during weekday peak periods and at intervals ranging from 8 to 12 minutes during off-peak times, with a fleet comprising between 9 and 15 trains (equivalent to 18 to 30 light rail vehicles).
Early Development
The initial segments that now form the B branch have their origins in the former Watertown Line and Beacon Street Line. In 1889, the West End Street Railway inaugurated the Beacon Street Line, which included a spur running from Coolidge Corner to Oak Square via Harvard Avenue, Brighton Avenue, Cambridge Street, and Washington Street. Although this route served expanding neighborhoods such as Allston and Brighton, there was demand for a more direct corridor. Enhancements made to Commonwealth Avenue between Governors Square and the junction at Brighton Avenue during the mid-1890s incorporated a -wide median dedicated to streetcar operations aimed at fostering real estate development. Service commenced on May 18, 1896, between Governors Square and Brighton Avenue, linking with pre-existing tracks at . By June 13, 1896, this line had extended close to Nonantum Square.
Further westward, a -wide median for streetcars was constructed between and the Boston–Newton boundary at Lake Street. Operations began on August 15, 1896, running from Lake Street into downtown Boston along Chestnut Hill Avenue, then connecting with the Beacon Street line, Washington Street, and continuing on Huntington Avenue. At Lake Street, passengers could transfer to the Commonwealth Avenue Street Railway, which had opened service to Auburndale earlier that March.
East of Governors Square, the Beacon Street line originally followed Beacon Street itself before turning onto Massachusetts Avenue and then onto Boylston Street, terminating at Park Square. Once Commonwealth Avenue segments were operational, streetcars proceeded along heavily trafficked Tremont Street tracks—electrified in 1891—to access northern railroad terminals. Both lines serving Nonantum Square and Lake Street were eventually rerouted into the newly constructed Tremont Street subway, ending their runs at Park Street station shortly after it opened on September 1, 1897.
The expansion continued under the management of the Boston Elevated Railway (BERy), which leased West End Street Railway starting October 1, 1897. On May 26, 1900, BERy unveiled new tracks along Commonwealth Avenue stretching from Chestnut Hill Avenue to Brighton Avenue. This allowed for direct service between Lake Street and downtown Boston via Commonwealth Avenue. Although much of Brighton remained undeveloped at that time, ridership levels were robust. Notably, most of this track laid in 1900 was positioned not within a central median but rather within a reserved strip situated between the southbound traffic lane and adjacent carriage lane; between and Wallingford Road, this reservation was particularly broad.
Expansion of Services
On June 17, 1897, the Commonwealth Avenue Street Railway inaugurated the well-known Norumbega Park. This line was integrated into the Newton and Boston Street Railway (N&B) in 1904 and later into the Middlesex and Boston Street Railway (M&B) by 1909. Starting January 17, 1903, BERy operated continuous service from Norumbega Park to Park Street station east of Lake Street. The Newton Street Railway, which also merged with N&B in 1904, began through service between Park Street and via the Watertown Line on February 23, 1903. Following the April 1912 opening of the Cambridge Tunnel, Waltham routes were redirected to Central Square station in Cambridge. On May 1, 1912, M&B introduced a second through route along Commonwealth Avenue reaching Newton Highlands.
The Boylston Street subway commenced operations on October 3, 1914, extending the Tremont Street subway beyond Governors Square with stops at Copley Square and Massachusetts Avenue. ( station was added in 1921.) Service via Washington Street to Lake Street was reduced except during peak periods. Newton Highlands through service was truncated to Lake Street, where passengers connected with BERy streetcars. Due to older M&B streetcars being unable to match BERy's subway speeds, Norumbega Park through service continued on surface routes. On November 1, this service branched at Lake Street with a connecting BERy line; by November 21, it was shortened to operate between Kenmore and Park Street.
By November 21, rush hour Washington Street service was curtailed to Reservoir, leaving only Beacon Street cars running on Chestnut Hill Avenue tracks. Beacon Street service itself was reduced to Reservoir on November 6, 1915; meanwhile, Washington Street service resumed up to Lake Street. Beginning February 6, 1922, Washington Street operated as a shuttle between Brookline Village and Lake Street, coordinated with Huntington Avenue line adjustments. This shuttle transitioned to bus operation on April 24, 1926, was rerouted to Brighton Center on June 23, 1928, and eventually became known as route 65.
The Commonwealth Avenue line provided access to key sports venues: Fenway Park, which opened in 1912 near Governors Square, and Braves Field, inaugurated in Allston in 1915. In that year, BERy implemented a prepayment surface station at Kenmore Street within Governors Square to expedite boarding processes. Braves Field opened August 18, 1915; it included a loop track equipped with a prepayment station enabling direct streetcar entry. This loop also facilitated train turnarounds for Red Sox games and rush-hour short-turn services; after November 1945 these short-turns operated midday and on Saturdays. During events such as the 1948 World Series, streetcars ran between Park Street and Braves Field at intervals as brief as every 45 seconds.
Subsequent Developments
Around 1916, BERy constructed a streetcar storage facility north of Commonwealth Avenue at Lake Street. By 1930, remaining M&B services to Lake Street were replaced by buses; concurrently, BERy enhanced the old transfer point by adding a new platform and waiting area within the yard on September 12 of that year. An expansion of Reservoir Yard near Chestnut Hill Avenue in May 1940 supplemented Lake Street Yard's capacity and allowed for the withdrawal of some Commonwealth Avenue streetcars from Bennett Street Carhouse in Cambridge.
In June 1922, BERy proposed transforming the inner Commonwealth Avenue line into rapid transit using three-car center-entrance trains designed for increased capacity and reduced stop times with headways as frequent as two minutes during peak hours. A terminal station was planned at Linden Street in Allston for transfers between subway trains and surface lines; however, local opposition caused its cancellation. The Lechmere Square station opened that July.
Due to congestion at Governors Square causing delays, the state legislature mandated in May 1924 that the Metropolitan District Commission devise plans for an expanded rapid transit system including an extension of the Boylston Street Subway beneath Governors Square. A report issued in December 1926 recommended reorganizing Boston’s streetcar tunnels into two rapid transit lines utilizing high-floor vehicles. One route would connect East Boston to Brighton by realigning the East Boston Tunnel to link with the Tremont Street subway near Park Street. The Boylston Street subway would be extended to Commonwealth Avenue featuring a new station under Governors Square; additionally, a transfer station near Brighton Center would connect rapid transit lines with shortened surface routes. Plans also included removal of busy grade crossings and several intermediate surface stops while noting potential future rapid transit expansion along Commonwealth Avenue up to Lake Street due to growth.
The Governors Square subway construction was estimated at $5 million (in 1926 dollars). Although BERy and the city initially proposed a $1.4 million flyover ramp alternative, they ultimately accepted the tunnel plan after legislative cost revisions. Construction commenced in 1930; Kenmore station opened alongside the new subway on October 23, 1932. This extension branched into separate portals at Saint Mary's Street on Beacon Street and Blandford Street on Commonwealth Avenue and supported prospective rapid transit upgrades along Commonwealth Avenue including further underground expansion.
Interest in converting the Commonwealth Avenue line waned as planning efforts shifted toward extending rapid transit into suburban areas via the Boston and Albany Railroad corridor while maintaining local streetcar operations along Commonwealth Avenue according to the Coolidge Commission reports of 1945 and 1947. Nonetheless, smaller enhancements were implemented: a siding at Washington Street (1926) facilitated short-turn operations; Beacon Street and Commonwealth Avenue lines extended service to Lechmere (1931), replacing shuttle routes; a pocket track west of Blandford Street (1931) was installed for temporary train storage; and route number reassignment occurred for Lake Street line around 1940. On May 6, 1940, operational control moved from Bennett Street Carhouse near Harvard Square to Reservoir Carhouse, reducing non-revenue moves along Cambridge Street.
Postwar period
During the early 1940s, the BERy initiated the replacement of outdated streetcars with PCC streetcar models, debuting them on the Lake Street route in May 1944 and completing the transition from center-entrance cars by December 10, 1945. Trackwork included reopening a brief segment of Chestnut Hill Avenue, which had been inactive since 1926, along with constructing a connecting track from westbound Commonwealth Avenue to southbound Chestnut Hill Avenue on May 31, 1947, thereby finalizing the wye junction between these avenues. Reflecting Boston College's growth, the BERy renamed the "Lake Street" line to "Boston College" on May 21, 1947. Subsequently, on August 29, 1947, the Metropolitan Transit Authority (MTA), a public entity, took over operations from the private BERy.
In January 1953, the seldom-used siding at Washington Street was removed, leaving only a crossover in place. The construction of the Massachusetts Turnpike Extension in April 1959 led to the closure of all Boston and Albany RailroadWorcester Line stations between and , making the Watertown and Boston College lines the only remaining rail transit services in Allston and Brighton. After acquiring Braves Field in 1953 following the Braves' move to Milwaukee, Boston University aimed to repurpose the loop area; after multiple petitions, the MTA discontinued this loop on January 15, 1962.
In 1960, modifications to Commonwealth Avenue’s streetcar reservation between Warren Street and Wallingford Road narrowed it to add additional traffic lanes, relocating tracks into a median separating travel lanes. On November 25, 1961, service on the Boston College line was truncated at Park Street station as the Riverside Line extended service to Lechmere. Between 1963 and 1965, reconstruction of the Commonwealth Avenue bridge over the Boston and Albany Railroad was undertaken to accommodate the Turnpike Extension; during this period, streetcars operated via a temporary adjacent bridge.
MBTA era
In August 1964, the Massachusetts Bay Transportation Authority (MBTA) replaced the MTA as operator. As part of a system-wide rebranding effort, all remaining streetcar routes serving the Tremont Street subway were collectively renamed the Green Line on August 26, 1965. The five branches were assigned letter designations in 1967: the Boston College route became the B branch; Watertown and Beacon Street lines were designated A and C branches respectively. The MBTA trialed various downtown terminals for Green Line branches; notably, in November 1964, the B branch was extended to a new loop at , becoming its first regular user. Over approximately twenty years, B branch termini shifted among Park Street, Government Center, , North Station, and Lechmere before settling at Government Center from 1983 through 2004.
On June 21, 1969, bus service Watertown–Kenmore replaced the A branch, reducing streetcar operations east of Packard's Corner by half. In 1970, alterations were made to medians between Chestnut Hill Avenue and Lake Street; westbound lanes were lowered near South Street and Greycliff Road with related stop relocations. By roughly 1975, several stops were either eliminated or repositioned to optimize operations.
The downtown terminus was extended to North Station on June 25, 2004 but reverted back to Government Center on January 1, 2005. It was further reduced to Park Street in March 2014 during Government Center’s reconstruction; after reopening in 2016, Park Street continued as the B branch terminus. On October 24, 2021, service resumed to Government Center ahead of the Green Line Extension launch to improve Blue Line connections and enhance downtown service distribution. From June 20 to July 1, 2022, buses replaced train service due to track maintenance and installation of a train protection system.
Stop Consolidation and Accessibility Improvements
The deployment of low-floor light rail vehicles (LRVs) in 2000 marked the beginning of accessible service along the Green Line. During the early 2000s, the MBTA enhanced several surface stops by adding raised platforms as part of the Light Rail Accessibility Program. Additionally, portable lifts were installed at and to assist passengers. Between 2002 and 2003, four surface stops—, Boston University Central, , and —were upgraded with raised platforms, while Boston College station received similar improvements in 2009.
The B branch has been criticized for sluggish service attributed to its numerous stops and level crossings. Before 2004, it featured 22 surface stops, which was more than other branches. To address this, the MBTA proposed in late 2003 the closure of five low-ridership stops situated close to others (Greycliff Road, , Mount Hood Road, Summit Avenue, and ) to enhance operational efficiency. After considering public input, Chiswick Road was spared from closure. The remaining four stops were closed in April 2004 on a trial basis; subsequent surveys indicated that 73% of riders supported the closures, leading to their permanent status in March 2005.
In 2014, plans were made to merge four non-accessible stops near Boston University's West Campus—, , , and —into two fully accessible stations. A contract valued at $17.8 million was awarded in March 2020 to reconstruct Commonwealth Avenue between the BU Bridge and Packard's Corner. Construction commenced in February 2021 and continued into early 2022, with bus replacements operating for much of 2021. The newly consolidated stations, Babcock Street and , officially opened on November 15, 2021.
Track maintenance conducted during 2018–19 prompted accessibility enhancements at various stops. By December 2022, design progress for , , Chiswick Road, , and had reached approximately 30%. In March 2024, released designs proposed consolidating Chestnut Hill Avenue and South Street into a single station. In May 2024, the Federal Transit Administration granted $67 million to the MBTA for constructing accessible platforms at fourteen stops along the B and C branches. The project expanded in 2024 to include five additional stations: Blandford Street is slated for closure; Griggs Street will undergo reconstruction; Allston Street and Warren Street will be merged; and Boston College will be relocated. As of February 2025, a $74 million design-build contract is scheduled for bidding in May 2025, with construction anticipated from fall 2025 through mid-2027.
In 2021, the MBTA revealed a longer-term vision that may involve replacing existing side platforms with wider island platforms at select or all surface stops. This extensive initiative—which encompasses station consolidation, upgrades, track realignment, and traction power improvements—is estimated to cost $221 million. Furthermore, plans include rebuilding and expanding Lake Street Yard to accommodate new Type 10 LRVs during the late 2020s.
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March 21, 2022
Original surface station operated July 10, 1922 – May 23, 2020; current station serves D and E branches.
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August 20, 1955
Serves D and E branches; B branch service ended March 21, 1980.
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June 28, 2004
Serves D and E branches; B branch service ceased December 31, 2004.
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September 3, 1898
Serves D and E branches; B branch service ended December 31, 2004.
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From a page move: This is a redirect from a page that has been moved (renamed). This page was kept as a redirect to avoid breaking links, both internal and external, that may have been made to the old page name.
When appropriate, protection levels are automatically sensed, described and categorized.
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From a page move: This is a redirect from a page that has been moved (renamed). This page was kept as a redirect to avoid breaking links, both internal and external, that may have been made to the old page name.
When appropriate, protection levels are automatically sensed, described and categorized.
