Draft:Proposed expansion of the MBTA subway
Since the opening of Boston's first subway line in 1897, and during the subway system's history, multiple official and planning agencies have proposed several extensions of the subway lines. The first major expansion of the subway system was the opening of the Boston Elevated Railway's main line in 1901, which utilized part of the Tremont Street Subway to carry it's trains under the city. The line was thus expanded into Charlestown and Roxbury, and it served as a predecessor for parts of the Orange Line and Silver Line.
Shortly after this expansion, the system continued to grow. The East Boston Tunnel opened in 1904, and provided a one-seat ride from East Boston to Downtown. The tunnel was the first in North America to go underwater, as it ran 2,700 feet (820 m) under Boston Harbor. This tunnel is still in use today, carrying the modern Blue Line from Bowdoin to Maverick. The line surfaces after Maverick and continues into Revere.
In 1909, construction began on a tunnel between Boston and Cambridge. This tunnel was proposed for years, but was ultimately delayed by the residents of the cities, who disagreed on how many stations were to be constructed. The tunnel finally opened in 1912, running from Harvard Square to Park Street. Several further extensions of the tunnel into South Boston continued between 1917 and 1928, and the line terminated at Ashmont. Today, this comprises much of the Red Line's Ashmont branch. A second branch of the line to Braintree opened in multiple segments between 1971 and 1983.
In recent times, many new proposals for the system have arisen, but few have actually been constructed. An extension of the Orange Line to Reading was partially constructed in 1977, but never fully completed due to a lack of funding. An extension of the Red Line to Lexington was also partially constructed in 1985, but never finished because of community opposition. Nearly three decades passed before another large expansion of the subway began construction, as an extension of the Green Line to Medford and Somerville began construction in 2017 and is planned to open in 2021.
Before unification of the subway system in 1964, several different subway and streetcar systems operated throughout Boston and surrounding areas. The Boston Elevated Railway initially provided service between Charlestown and Roxbury, before several expansions pushed service further south and north. The East Boston Tunnel initially provided service between East Boston and Downtown, until the line was extended further east into Revere. The Cambridge Tunnel began operations between Park Street and Harvard Square in 1912, and was extended south several times, with the line eventually terminating in Dorchester.
May 1900 Plan
During the planning stages for the East Boston Tunnel, an engineering plan released in May 1900 revealed that the tunnel was to connect East Boston with Cambridge, as the termini of the line was planned to be Harvard Square and Maverick Square. This tunnel would have used bi-level loading cars, as the cars would have been used as both rapid-transit cars and surface-level trolley cars. After a series of disagreements between the Boston Elevated Railway and the Boston Transit Commission, the plan was dropped.
During this short three-year period, several proposals for both the East Boston Tunnel and the Elevated Main Line pushed service into the suburbs.
- Shortly after the line began operations in 1904, Atlantic Avenue station opened on the East Boston Tunnel, providing a transfer to the State Street station on the Atlantic Avenue Elevated through a three-story tall system of wooden escalators and fare lobbies.
- Around the same time, Court Street station began to be problematic for the line, as the station was only single-tracked. As the station was the western terminus of the line, this design prevented frequent service to the station and also resulted in crashes. The Boston Elevated Railway proposed closing the station and extending service into Beacon Hill. Construction of Bowdoin began in 1912, and the station was opened in 1916.
- Calls for improved streetcar service to Cambridge prompted a proposal to build an elevated railway bridge connecting Boston and Cambridge. Construction on this extension, known as the Lechmere Viaduct began in 1907.
- In 1908, the Washington Street Tunnel opened, allowing the Boston Elevated Railway's Main Line to travel between the Charlestown Elevated and the Dudley Square station without using the Tremont Street Subway. This allowed for the Tremont Street Subway to be used solely by streetcars.
- In 1909, the Boston Elevated Railway's Main Line was extended southward to Forest Hills on the Washington Street Elevated. Egleston, a station located in Roxbury, opened on the same day. 
The subway system continued to grow with the opening of both the Cambridge Tunnel and the Lechmere Viaduct in 1912. A section of the Boylston Street Subway opened shortly after in 1914, connecting to the Tremont Street Subway.
- In March 1912, the Cambridge Tunnel opened between Harvard Square and Park Street, with additional stations at Central Square and Kendall Square. The tunnel's opening was significantly delayed because of a dispute regarding the number of stations to be built between Park Street and Harvard Square. Mayor Wardwell, along with many Cambridge residents wanted five intermediate stations to be built on the line, but many Boston residents only wanted a single station to be built at Central Square, citing that additional stations would lengthen travel times on the line. Only building two intermediate stations was agreed upon in 1909, and construction commenced.
- In June 1912, the Lechmere Viaduct began operating, it carried streetcars across the Charles River into Cambridge. It was proposed several years earlier, and construction began in 1909. It was built to allow streetcars to easily get from Boston to Cambridge, as streetcars originally had to use the oft-busy Craigie Bridge.
- Jamaica Plain (renamed Green Street in 1940), an infill station on the Washington Street Elevated, opened between Forest Hills and Egleston in September 1912.
- The Boylston Street Subway opened in 1914, connecting to the Tremont Street Subway at it's easternmost end. The subway ran from Boylston station westward to the Kenmore Incline. Two intermediate stations, Massachusetts (later renamed Hynes Convention Center), and Copley, opened along with the line.
- The first part of the Dorchester Tunnel opened in April 1915, it extended service on the Cambridge Tunnel to Washington station. A further extension of the tunnel to South Station Under opened in December 1916.
- Bowdoin station opened in 1916 as part of an extension of the East Boston Tunnel to Beacon Hill. An intermediate station at Scollay Under opened on the same day.
Between 1917 and 1929, the Cambridge-Dorchester Line was extended further south to Andrew Square in South Boston. A proposal to extend the line even further along the right-of-way of the former Shawmut Branch Railroad caused the line to eventually terminate at Ashmont station. The Ashmont–Mattapan High Speed Line also opened in two phases in 1929.
- In December 1917, Broadway station opened on the Cambridge-Dorchester Line, with Andrew Square following suit six months later. These extensions of the Cambridge-Dorchester line opened station-by-station instead of all at once due to the popularity and demand for the stations.
- A proposal to extend the Charlestown Elevated from Sullivan Square to Malden was partially constructed, as the line was extended to Everett station.
- In 1921, Arlington, an infill station on the Boylston Street Subway opened. Many businesses in the area lobbied for a new station at Arlington Street, citing that they could lose money because of the lack of a nearby station. Mayor James Michael Curley supported the idea for a new station, and the proposal was later approved. Opening of the station was delayed for years because of World War I.
- In March 1923, a proposal to create a new trolley line between Ashmont and Mattapan was approved. The line opened six years later.
- In 1924, after three years of planning and proposals, the East Boston Tunnel was converted from streetcar use to third rail-powered rapid transit. This change took only a single weekend to complete, and was built by nearly 1,500 men.
- The Dorchester Extension opened in two phases; the first opened in November 1927, and the second in September 1928. The first phase opened from Andrew Square to Fields Corner, with intermediate stops at Columbia (now JFK/UMass) and Savin Hill. The second phase extended service to Ashmont/Peabody Square, with a single intermediate stop at Shawmut. The entire extension was built over the right-of-way of the former Shawmut Branch Railroad.
- In 1929, the Ashmont–Mattapan High Speed Line opened in two phases. The first phase opened from Ashmont to Milton in August 1929. An intermediate station also opened at Cedar Grove during phase 1. A second phase from Milton to Mattapan opened in December 1929. Phase 2 also included two intermediate stations at Central Avenue and Valley Road.
During the last years of the Boston Elevated Railway, several streetcar lines connected with the Boylston Street Subway, to form parts of the present-day Green Line. The Atlantic Avenue Elevated also closed during this time.
- In February 1932, Charles opened as an infill station on the Cambridge-Dorchester Line. The station was renamed "Charles/MGH" in 1973 after the nearby Massachusetts General Hospital.
- A station at Kenmore Square opened on the Boylston Street Subway in October 1932. This station replaced the former Kenmore Portal. The portal was replaced by the St. Mary's Street Portal on the Beacon Street Line (later the "C" Branch), and the Blandford Street Portal on both the Watertown and Commonwealth Avenue branches (later the "A" and "B" branches, respectively).
- Due to poor ridership, the Atlantic Avenue Elevated was closed in 1938. It was demolished four years later.
- In early 1941, the Huntington Avenue Subway opened, branching off from the Boylston Street Subway shortly after Copley. Mechanics and Symphony are the only two stations underground, as the Northeastern Portal brings the line to street level shortly after Symphony. The portal opened in 1941, and was built as a wooden trestle, as a proposal to extend the subway even further down Huntington Avenue was initially considered but ultimately never built. After the portal, the Huntington Avenue Branch continued to Arborway station in Jamaica Plain. 22 intermediate stations between Symphony and Arborway opened along with the subway.
Red Line Historical Routes from 1912 to 1946
Orange Line Historical Routes from 1901 to 1946
Blue Line Historical Routes from 1904 to 1946
- Cheney, Frank (7 April 2004). Boston's Blue Line. Arcadia Publishing. pp. 11–12. ISBN 978-0-7385-3576-0.
This May 1900 engineering plan shows the East Boston Tunnel as outfitted for use by elevated trains on the planned Harvard Square-Maverick Square line. The plan was dropped as a result of continued heated disagreements between the Boston Elevated and the Boston Transit Commision.
- Chasson, George Jr. (1987). Lonto, Arthur J. (ed.). "Boston's Main Line El: The Formative Years 1879–1908". Headlights. Electric Railroader's Association. 49: 16, 57.
- Clarke, Bradley H.; Cummings, O.R. (1997). Tremont Street Subway: A Century of Public Service. Boston Street Railway Association. ISBN 0938315048.
- Koebel, Romin (2005). "Boston Transit Milestones". MIT Open Courseware. Archived from the original on 2006-09-20. Retrieved 2017-08-05.
- Belcher, Jonathan (5 August 2017). "Changes to Transit Service in the MBTA district" (PDF). NETransit. Retrieved 6 August 2017.
- Cudahy, Brian J. (1972). Change at Park Street Under: The Story of Boston's Subways. Brattleboro, Vermont, US: Stephen Greene Press. ISBN 0-8289-0173-2.
- "STATE AND CITY OFFICIALS INSPECT NEW ELEVATED: East Cambridge Extension For Surface Cars Will Reduce Running Time From North Station to Three Minutes". Boston Globe. 28 May 1912. Retrieved 5 August 2017 – via ProQuest Historical Newspapers.
- O'Regan, Gerry. "MBTA Orange Line". Retrieved 8 August 2017.
- "Officials Celebrate Modernization of Arlington Station". MBTA.com. Massachusetts Bay Transportation Authority. 2009-06-01. Retrieved 2017-08-06.
- Cheney, Frank (2002). Boston's Red Line: Bridging the Charles from Alewife to Braintree. Arcadia Publishing. pp. 6–8, 66–67. ISBN 9780738510477.
- O'Regan, Gerry. "MBTA Red Line". Retrieved 8 August 2017.
- O'Regan, Gerry. "MBTA Green Line". Retrieved 8 August 2017.