The Green Line is a light rail system run by the Massachusetts Bay Transportation Authority (MBTA) in the Boston, Massachusetts, metropolitan area. It is the oldest MBTA subway line, and with tunnel sections dating from 1897, the oldest subway in North America. It runs underground through downtown Boston, and on the surface into inner suburbs via six branches on radial boulevards and grade-separated alignments. With an average daily weekday ridership of 130,059 in July 2026, it is among the most heavily used light rail systems in the United States. The line was assigned the green color in 1967 during a systemwide rebranding because several branches pass through sections of the Emerald Necklace of Boston.
The four branches are the remnants of a large streetcar system, which began in 1856 with the Cambridge Horse Railroad and was consolidated into the Boston Elevated Railway several decades later. The branches all travel downtown through the Tremont Street subway, the oldest subway tunnel in North America. The Tremont Street subway opened its first section on September 1, 1897, to take streetcars off overcrowded downtown streets; it was extended five times over the next five decades. The streetcar system peaked in size around 1930 and was gradually replaced with trackless trolleys and buses, with cuts as late as 1985. The new D branch opened on a converted commuter rail line in 1959. The Green Line Extension project extended two branches into Somerville and Medford in 2022.
Route description The Green Line's core is the central subway, a group of tunnels which run through downtown Boston. The Tremont Street subway runs roughly north–south through downtown, with stations at , , , , and – all with connections to other lines of the MBTA subway system. The Boylston Street subway runs roughly east–west through the Back Bay neighborhood, with stations at , , , and ; it connects to the Tremont Street subway at Boylston. The Huntington Avenue subway diverges from the Boylston Street subway at a flat junction west of Copley, running southwest, with stations at and . A branch of the Tremont Street subway, disused since 1962, runs south from Boylston to the former Pleasant Street incline.
The Green Line has four western surface branches, each with a letter designation: The B branch runs west in a tunnel from Kenmore, surfacing in the median of Commonwealth Avenue at . It runs on Commonwealth Avenue through Boston University, Allston, and Brighton to Boston College station. The C branch runs southwest in a tunnel from Kenmore, surfacing in the median of Beacon Street at . It runs on Beacon Street through Brookline to Cleveland Circle station. The D branch diverges from the C branch tunnel southwest of Kenmore, surfacing at Fenway station. It runs though Brookline and Newton along the grade-separated Highland branch (a former Boston and Albany Railroad commuter rail line) to Riverside station. The E branch runs southwest through the Huntington Avenue subway from Copley, surfacing in the median of Huntington Avenue at Northeastern University station. It runs along Huntington Avenue and South Huntington Avenue to , with the outer (west of ) in mixed traffic rather than a dedicated median. Until 1985, the line continued south through Jamaica Plain to .
B and C branch service terminates at Government Center, while D and E branch service continues north from downtown Boston. North of North Station, the line inclines up to the Lechmere Viaduct, which crosses the Charles River with an elevated station at . The elevated Lechmere station is located on the Green Line Extension viaduct, which continues north to a flying junction with two branches: The Union Square Branch runs west to Union Square station via the Fitchburg Line right-of-way. It is operated as part of the D branch. The Medford Branch runs northwest to Medford/Tufts station via the Lowell Line right-of-way. It is operated as part of the E branch.
Former branches
The Green Line A branch was the northernmost of the branches, running from the Blandford Street portal (still used by the B branch), west to Watertown, mostly street-running. The bus replaced the streetcar line in 1969. The A branch diverged from Commonwealth Avenue west of Boston University and ran to a terminus in Watertown, across the Charles River from Watertown Square, until 1969. Although the route-letter scheme had been introduced two years prior to its closure, the "A" designation was never signed on streetcars to Watertown. It was, however, included in the destination signs on the Boeing-Vertol LRVs ordered in the mid-1970s, when reopening service to Watertown was under consideration. The "A" line tracks remained in non-revenue service to access maintenance facilities at Watertown until 1994.
The Pleasant Street portal hosted two services in its final days. Route to City Point ended in 1953; route to was cut back to Lenox Street in 1956, cut back to the portal in 1961, and ended operation in 1962. Prior to that, route 48 serviced Tremont Street to Dover Street and Washington Street, ending at , and last running in 1938.
The last two routes to continue beyond the Canal Street portal both ran to . The ran via Main Street, last running in 1948, and the via Bunker Hill Street last ran in 1949. Until 1997, trains continued to use the portal and its North Station surface station as a terminal.
In addition to the lines that later became the E branch, the Ipswich Street line split in Brookline, one branch running into the current "E" tracks and into the Boylston Street portal, and the other running up Brookline Street to end at Massachusetts Avenue station. These were truncated in 1932 into a shorter route from Brookline Village to the subway via the Boylston Street portal.
The last "foreign" cars to operate in the subway were those of the Eastern Massachusetts Street Railway, running from the Canal Street portal to the Brattle Loop at Scollay Square until 1935. It was then that the old Mystic River Bridge to Chelsea was closed to streetcars and the lines were replaced by bus service; the next year the Boston Elevated Railway (BERy) bought the Eastern Mass Chelsea Division and through-routed it with its lines connecting to the East Boston Tunnel at Maverick.
Rolling stock Like the three other MBTA subway lines, the line uses standard gauge tracks. However, instead of heavy rail metro rolling stock, the Green Line uses modern streetcars (light rail vehicles) as heavy rail stock would be inappropriate for the surface branches with their numerous grade crossings.
Listing Active fleet Rolling stock : Year builtManufacturerModelImageLengthWidthFleet numbersQuantity 1986–1988 Kinki Sharyo Type 7 LRV 3600–3699 100 (70 active, all overhauled) 1997 3700–3719 20 (14 active, all overhauled) 1998–2007 AnsaldoBreda Type 8 LRV 3800–3894 95 (72 active)2018–2020CAF USA Type 9 LRV 3900–3923 24 (all active)
Non-revenue work cars include #3615 and #3669.
Retired fleet Only MBTA operated vehicles are included here, not cars from the Boston Elevated Railway era.
Years in ServiceManufacturerModelImageLengthWidthFleet numbersQuantity 1976–2007 Boeing Vertol US Standard Light Rail Vehicle 3400–3543 144 (31 units cancelled) 1937–1985 Pullman Standard PCC streetcar 3000–3346 344 (2 cars scrapped before 1964)
Future Years BuiltManufacturerModelImageLengthWidthFleet numbersQuantity2027–2031CAF USAType 10 LRV4001–4102102 (pilot car #4002 arived in September 2026, to enter service in 2027)
History Early rolling stock
When it opened at the end of the 19th century, the Tremont Street subway was not intended as a full-scale rapid transit line, but to allow ordinary streetcars to bypass the worst street congestion in downtown Boston. Operations by several different companies were eventually consolidated into the Boston Elevated Railway, which ran a mixture of car types. After receiving a test unit in 1937, the BERy began to standardize on PCC streetcars, acquiring 320 units between 1941 and 1951 plus an additional 25 in 1959 to phase out the last older cars. Beginning in 1923, all streetcars on the system were painted orange for maximum visibility in traffic. In 1971, the MBTA began painting Green Line streetcars in a green and white scheme to match the new line name.
Two older streetcars are on display on the unused outer inbound track at Boylston station, which formerly carried cars coming from the Pleasant Street portal. Car #5734, a Type 5 A-1 car built in 1924 and retired in 1959, is owned by the Seashore Trolley Museum, but resides semipermanently in Boston. PCC #3295, built in 1951 and retired in 1986, is owned by the MBTA. The cars were formerly used for fantrips, the most recent one being in 1998.
Boeing LRV
In the early 1970s, light rail—which had largely disappeared from North America after the slow decline of streetcar systems from the 1920s to the 1950s—was reintroduced as a method of urban renewal less expensive than conventional metro systems. In 1971, as part of a program to supply further work to defense contractors as the Vietnam War wound down, the Urban Mass Transit Administration selected Boeing Vertol as systems manager for a project to design a new generic light rail vehicle. The UMTA hoped that this "US Standard Light Rail Vehicle" would jumpstart the development of transit lines just as the standardized PCC streetcars had done decades prior.
Boston (with its older streetcar tunnel systems) and San Francisco (with a new Muni Metro streetcar tunnel being built as part of BART construction) were chosen as the testbeds for this new rolling stock. The vehicle was designed as the largest rolling stock that would fit through the Tremont Street tunnel, the Muni Metro's Twin Peaks Tunnel, and SEPTA's subway–surface lines tunnel. The new cars were faster—a top speed of versus the PCC's —and had an articulated middle section for higher capacity.
Boeing began construction of 175 cars for the MBTA in May 1973. The first LRVs entered service on the D branch in December 1976 but were immediately beset with problems. Certain cars frequently derailed on tight turns in the Riverside, Boston College and Lechmere yards. Battery trays, air conditioners—mounted under the cars, continually drawing in dirt and debris from under the car when in the tunnels—and air compressors all suffered numerous failures; the plug-style doors had trouble sealing properly; and traction motors failed sooner than expected.
Desperate for reliable rolling stock, in 1977 MBTA launched an overhaul program to extend the availability of its older PCC cars. A total of 34 cars, primarily out-of-service wrecks and parts cars, were rebuilt to as-new condition. , some of these rebuilt PCC cars still run on the Mattapan Line.
After years of fighting between the MBTA and Boeing-Vertol, both sides reached a settlement in 1979. MBTA was allowed to reject the final 40 SLRVs, and Boeing would return $40 million to MBTA for the cost of repairs and modifications to several cars.
Modern fleet
In the early 1980s, with a final settlement with Boeing in place, MBTA started looking for new equipment to supplement and replace the problematic LRVs.
In 1980, the MBTA tested Canadian Light Rail Vehicles for three months to determine whether they could be used on the Green Line. The MBTA ultimately found them unsuitable.
Ultimately, the MBTA purchased LRVs from the Japanese firm Kinki Sharyo. These Type 7 were designed with the best features of the US SLRV, the Canadian LRV, and the PCC cars. A total of 120 Type 7 vehicles were purchased, 100 were delivered between 1986 and 1988, and an additional 20 cars ordered and delivered in 1997.