Central subway (Boston)

Boston's central subway refers to the underground tunnel system utilized by the MBTA Green Line for light rail transit (LRT) within the city's downtown area. This network comprises tunnels constructed during various periods, including the Tremont Street subway, Boylston Street subway, and the Huntington Avenue subway.

Additionally, the MBTA classifies the heavy rail tunnels of the Red Line and Orange Line as components of the central subway infrastructure.

History

During the early to mid-1900s, what was then called the trolley subway accommodated at least seven different trolley lines utilizing diverse rolling stock. The initial vehicles were single-car electric streetcars powered by trolley poles collecting electricity from overhead wires, a system Boston had implemented for roughly ten years. Upon its inauguration in 1897, the Tremont Street subway managed upwards of 280 trolleys per hour, greatly alleviating surface traffic congestion.

Following Frank Sprague's introduction of electric multiple unit (EMU) trains in Chicago in 1897, Boston incorporated EMUs several years later on elevated routes predominantly serving the West End. By 1901, Boston's first underground EMU service began operating on adapted tracks and platforms within the Tremont Street subway. These heavy-rail corridors eventually developed into the present-day MBTA Red, Orange, and Blue lines, which share certain tunnels and stations with the Green Line.

In 1908, the Washington Street tunnel was launched parallel to the Tremont Street subway between Haymarket station and North Station, designated exclusively for heavy rail traffic. This change allowed the Tremont Street subway to be dedicated solely to light rail operations.