The B branch, frequently referred to as the Commonwealth Avenue branch or the Boston College branch, constitutes a vital portion of the MBTAGreen Line light rail network, operating along Commonwealth Avenue to the west of central Boston, Massachusetts. As one of the Green Line's four distinct branches, the B branch extends from Boston College station through the median strip of Commonwealth Avenue until it reaches , where it enters the Blandford Street portal, leading into Kenmore station. At Kenmore, it converges with the C and D branches before proceeding through the Boylston Street subway and Tremont Street subway en route to downtown Boston. Since October 2021, service on the B branch terminates at . Unlike its counterparts, the B branch operates exclusively within Boston city boundaries. The well-known Green Line Rivalry between Boston College and Boston University derives its name from this line, which provides transit access to both institutions.
As of , trains on this branch run every 8 minutes during weekday peak periods and every 8 to 12 minutes during off-peak times, utilizing between 9 and 15 trains (equivalent to 18 to 30 light rail vehicles).
Early development
The foundations of what is now the B branch trace back to segments of 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, passing through Harvard Avenue, Brighton Avenue, Cambridge Street, and Washington Street. While this route served expanding suburbs such as Allston and Brighton, there was demand for a more direct alignment.
During the mid-1890s, enhancements were made along Commonwealth Avenue between what was then known as Governors Square and Brighton Avenue junction. These improvements featured a 33-foot-wide median intended for streetcar operation aimed at encouraging real estate growth in the area. Service commenced on May 18, 1896, running from Governors Square to Brighton Avenue and connecting with pre-existing tracks at . By June 13, 1896, this line had been extended to near Nonantum Square.
Further westward development included constructing a 25-foot-wide streetcar median between and the Boston–Newton boundary at Lake Street. Service linking Lake Street directly with downtown Boston began on August 15, 1896. This route utilized Chestnut Hill Avenue, the Beacon Street line, Washington Street, and Huntington Avenue. At Lake Street, it connected with the Commonwealth Avenue Street Railway, which had opened its line to Auburndale in March 1896.
Initially east of Governors Square, the Beacon Street line followed Beacon Street, then proceeded along Massachusetts Avenue and Boylston Street to reach Park Square. Upon opening of the Commonwealth Avenue sections, streetcars continued along heavily congested Tremont Street tracks—which had been electrified in 1891—to access northern railroad terminals. Both Nonantum Square and Lake Street routes were soon redirected into the newly opened Tremont Street subway, terminating at Park Street station shortly after its inauguration on September 1, 1897.
The Boston Elevated Railway (BERy) took over operations by leasing West End Street Railway on October 1, 1897, furthering expansion efforts. On May 26, 1900, BERy introduced new tracks along Commonwealth Avenue stretching from Chestnut Hill Avenue to Brighton Avenue. This enabled direct streetcar service from Lake Street downtown via Commonwealth Avenue. Although much of Brighton's surrounding land remained undeveloped at that time, this heavily trafficked line mostly operated within a reservation located between southbound traffic lanes rather than occupying a central median. Notably, between and Wallingford Road, this reservation was significantly wider than typical track right-of-way.
Expansion of Service
The Commonwealth Avenue Street Railway inaugurated the well-known Norumbega Park on June 17, 1897. This route later became part of the Newton and Boston Street Railway (N&B) in 1904 and subsequently integrated into the Middlesex and Boston Street Railway (M&B) by 1909. Beginning January 17, 1903, through service connecting Norumbega Park and Park Street station commenced, with the eastern segment from Lake Street operated by BERy. The Newton Street Railway, which merged into N&B in 1904, initiated through service between Park Street and via the Watertown Line on February 23, 1903. After the opening of the Cambridge Tunnel in April 1912, services to Waltham were rerouted to stop at Central Square station in Cambridge. On May 1, 1912, M&B launched an additional through service along Commonwealth Avenue extending to Newton Highlands.
The Boylston Street subway became operational on October 3, 1914, extending the Tremont Street subway eastward to just beyond Governors Square with stations at Copley Square and Massachusetts Avenue. ( station was added in 1921.) Service from Lake Street via Washington Street was shortened to , except during peak hours. Through service to Newton Highlands was curtailed back to Lake Street to facilitate transfers with BERy streetcars. Norumbega Park continued to be served by surface routes since older M&B cars could not match the speed of BERy’s subway operations; this division took effect at Lake Street on November 1, with a connecting BERy line operating on the surface route that was later truncated to a Kenmore–Park Street route.
On November 21, rush hour Washington Street service was reduced to Reservoir, leaving Beacon Street cars as the only users of tracks along Chestnut Hill Avenue. Beacon Street service was cut back to Reservoir on November 6, 1915, while Washington Street service extended again to Lake Street. Starting February 6, 1922, Washington Street operated a shuttle service between Brookline Village and Lake Street alongside changes on the Huntington Avenue line. This shuttle transitioned to bus operation on April 24, 1926, eventually becoming route 65 after being redirected to Brighton Center in 1928.
Commonwealth Avenue line provided access to major baseball stadiums: Fenway Park (opened in 1912) near Governors Square and Braves Field (opened in 1915) located in Allston. In 1915, BERy introduced a prepayment surface station at Kenmore Street within Governors Square to expedite passenger boarding. Braves Field featured a loop track with a prepayment station that allowed direct streetcar entry starting August 18, 1915. This loop also facilitated turning trains for Red Sox games at Fenway Park and managed rush-hour short-turn operations; after November 1945 these short turns operated during midday hours and Saturdays as well. During the 1948 World Series, streetcars ran between Park Street and Braves Field at intervals as frequent as every 45 seconds.
Subsequent Developments
Around 1916, BERy constructed a streetcar storage yard north of Commonwealth Avenue at Lake Street. Remaining M&B services terminating at Lake Street were replaced by buses in 1930; on September 12 of that year, BERy substituted the old transfer station located in the median with a new platform and waiting facility within the yard. An expansion of Reservoir Yard—situated south of Beacon Street near Chestnut Hill Avenue—was completed in May 1940 to supplement Lake Street Yard and eliminated the necessity of housing some Commonwealth Avenue streetcars at Bennett Street Carhouse in Cambridge.
In June 1922, BERy proposed converting the inner section of Commonwealth Avenue line into rapid transit using three-car center-entrance trains designed for increased capacity and reduced dwell times. Planned frequencies included trains every two minutes during rush hours and every four minutes during off-peak periods. A terminal station was envisioned at Linden Street (near Harvard Avenue) in Allston for transfers between subway trains and surface streetcars. However, local opposition led to abandonment of this plan. Meanwhile, Lechmere Square station in East Cambridge opened that July.
Due to congestion issues at Governors Square causing delays, the state legislature mandated planning in May 1924 for an expanded rapid transit network that included extending the Boylston Street Subway beneath Governors Square. A report published in 1926 recommended reorganizing Boston’s streetcar tunnels into two rapid transit lines utilizing high-floor cars: one running from East Boston to Brighton connecting the East Boston Tunnel with the Tremont Street subway near Park Street; and another extending the Boylston Street subway westward along Commonwealth Avenue featuring a new Governors Square station. A transfer station was proposed at Warren Street near Brighton Center with intermediate stops at Saint Mary’s Street, Gaffney Street, Packards Corner, Harvard Avenue, and Allston Street. The plan also called for eliminating several grade crossings and noted potential future rapid transit extension toward Lake Street due to growth along Commonwealth Avenue.
The Governors Square subway was estimated to cost $5 million in 1926 dollars. BERy and city officials suggested a more economical $1.4 million flyover ramp alternative but ultimately accepted construction of the tunnel after legislative adjustments lowered BERy’s rental expenses. Construction commenced in 1930; Kenmore station along with the new subway featuring portals at Saint Mary’s Street (Beacon Street) and Blandford Street (Commonwealth Avenue) opened on October 23, 1932. This extension supported potential future conversion of Commonwealth Avenue line into rapid transit as well as further underground expansion westward.
Interest in transforming Commonwealth Avenue line into rapid transit diminished as priorities shifted toward suburban expansion projects. The Coolidge Commission reports from 1945 and 1947 recommended establishing a parallel rapid transit line along the Boston and Albany Railroad corridor while maintaining local streetcar service on Commonwealth Avenue. Nonetheless, several improvements were implemented: a siding opened at Washington Street in October 1926 for short-turn operations; Beacon Street and Commonwealth Avenue lines extended service to Lechmere in February 1931 replacing shuttle routes; a pocket track west of Blandford Street installed in June 1931 allowed temporary storage of streetcars replacing earlier surface short turns at Kenmore starting September 1934; route number 62 was assigned around 1940; and on May 6, 1940 operations shifted from Bennett Street Carhouse near Harvard Square to Reservoir Carhouse eliminating deadhead moves along Cambridge Street.
Postwar period
During the early 1940s, the BERy initiated the replacement of aging streetcars with PCC streetcar models, initially introducing them on the Lake Street route in May 1944 and completing the phase-out of center-entrance cars by December 10, 1945. The Chestnut Hill Avenue tracks, which had been out of use since 1926, were upgraded to accommodate PCC streetcars, including the addition of a connecting track forming a wye between Commonwealth Avenue and Chestnut Hill Avenue by May 31, 1947. Reflecting the growth of Boston College, the BERy renamed the "Lake Street" line to "Boston College" on May 21, 1947. On August 29, 1947, the privately held BERy was replaced by the publicly operated Metropolitan Transit Authority (MTA).
In January 1953, the siding on Washington Street was removed, leaving only a crossover in place. The closure in April 1959 of Boston and Albany Railroad Worcester Line stations between and due to Turnpike Extension construction meant that the Watertown and Boston College lines remained the only rail transit options serving Allston and Brighton. Following Boston University's purchase of Braves Field in 1953 after the Braves' relocation to Milwaukee, plans were made to repurpose the loop area; consequently, the MTA discontinued use of the loop on January 15, 1962.
In 1960, modifications along Commonwealth Avenue involved narrowing the streetcar reservation between Warren Street and Wallingford Road to create additional travel lanes, relocating tracks to a median situated between these lanes. On November 25, 1961, service on the Boston College line was truncated to 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 took place to accommodate the Turnpike Extension; streetcar operations continued throughout this period via a temporary bridge constructed alongside.
MBTA era
In August 1964, the Massachusetts Bay Transportation Authority (MBTA) succeeded the MTA. As part of a systemwide rebranding effort, all remaining streetcar routes feeding into the Tremont Street subway were collectively designated as the Green Line on August 26, 1965. Two years later in 1967, each of the five branches received letter designations: the Boston College line became known as the B branch, while Watertown and Beacon Street lines were labeled A and C branches respectively. The MBTA experimented with more frequent changes to downtown terminals for Green Line branches compared to previous operators. Notably, in November 1964, the B branch was extended to serve a new loop at , marking its first regular use. Over a span exceeding twenty years, termini for the B branch shifted among Park Street, Government Center, , North Station, and Lechmere stations before settling at Government Center from 1983 until 2004.
On June 21, 1969, streetcar service east of Packard's Corner on Commonwealth Avenue was reduced when buses replaced the A branch with Watertown–Kenmore bus service. Infrastructure improvements in 1970 included shifting the median slightly southward between Chestnut Hill Avenue and Lake Street and lowering the westbound roadway between South Street and Greycliff Road; these changes also prompted relocation of several stops. Around 1975, some stops were consolidated or repositioned to enhance operational efficiency.
The downtown terminus was extended to North Station on June 25, 2004 but was subsequently shortened back to Government Center on January 1, 2005. It experienced a further reduction to Park Street in March 2014 during Government Center’s renovation; when reopening occurred in 2016, Park Street remained as the terminus. On October 24, 2021, ahead of the Green Line Extension launch, B branch service was once again extended back to Government Center to improve connections with the Blue Line and better distribute downtown transit demand. Trackwork and installation of train protection systems led to a temporary bus substitution for B branch service from June 20 through July 1, 2022.
Accessibility Enhancements and Stop Consolidation
The deployment of low-floor light rail vehicles (LRVs) in 2000 facilitated accessible service along the Green Line. During the early 2000s, the MBTA undertook upgrades at several surface stops as part of the Light Rail Accessibility Program, which included installing portable lifts at and around that time. Between 2002 and 2003, four surface stops—, Boston University Central, , and —were retrofitted with raised platforms to improve accessibility; Boston College received similar modifications in 2009.
The B branch has been criticized for its slow travel times, attributed to its numerous stops and frequent level crossings. Prior to 2004, it featured 22 surface stops, significantly more than the C and D branches (13 stops each) and the E branch (9 stops). To enhance operational efficiency, the MBTA proposed in late 2003 to eliminate five low-ridership stops: Greycliff Road, , Mount Hood Road, Summit Avenue, and . Following community input, Chiswick Road was excluded from this plan. On April 20, 2004, a pilot closure of the remaining four stops was implemented; after a rider survey indicated a 73% approval rate, these closures were made permanent on March 15, 2005.
In 2014, plans were announced to consolidate four non-accessible stops near Boston University's West Campus—, , , and —into two fully accessible stations as part of the Commonwealth Avenue reconstruction project. A contract valued at $17.8 million was awarded in March 2020. Construction commenced in February 2021 and concluded in early 2022, with bus substitutions covering much of 2021. The newly built stations—Babcock Street and —opened on November 15, 2021.
Track maintenance conducted during 2018–19 prompted accessibility improvements at multiple stops. By December 2022, design progress for , , Chiswick Road, , and had reached approximately 30%. A design proposal released in March 2024 recommended merging Chestnut Hill Avenue and South Street stations into a single facility. In May 2024, the Federal Transit Administration awarded $67 million to support accessible platform construction at fourteen B and C branch stations. Additionally, five more stations were incorporated into the project in 2024: Blandford Street will be closed; Griggs Street will undergo reconstruction; Allston Street and Warren Street will be combined; 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 to span from fall 2025 through mid-2027.
In 2021, the MBTA revealed plans for a longer-term initiative that may replace existing side platforms with wider island platforms at some or all surface stops. This extensive station consolidation and upgrade plan—including track realignment and improvements to traction power—is projected to cost approximately $221 million. Furthermore, reconstruction and expansion of Lake Street Yard are planned for the late 2020s to accommodate new Type 10 LRVs.
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March 21, 2022
Original surface station operated July 10, 1922–May 23, 2020; B branch service ended March 21, 1980. Currently serves D and E branches.
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August 20, 1955
Serves D and E branches; B branch service discontinued March 21, 1980.
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June 28, 2004
Currently serves D and E branches; B branch service ended December 31, 2004.
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September 3, 1898
Currently serves D and E branches; B branch service terminated 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.
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