<Tr> <Th> Added to NRHP </Th> <Td> October 15, 1966; 51 years ago (1966 - 10 - 15) </Td> </Tr> <Tr> <Th> Designated NHL </Th> <Td> January 29, 1964; 53 years ago (1964 - 01 - 29) </Td> </Tr> <P> The Tremont Street Subway in Boston's MBTA Subway system is the oldest subway tunnel in North America and the third oldest worldwide to exclusively use electric traction (after the City and South London Railway in 1890, and the Budapest Metro's Line 1 in 1896), opening on September 1, 1897 . It was originally built to get streetcar lines off the traffic - clogged streets, instead of as a true rapid transit line . It now forms the central part of the Green Line, connecting Boylston Street to Park Street and Government Center stations . </P> <P> The tunnel originally served five closely spaced stations: Boylston, Park Street, Scollay Square, Adams Square, and Haymarket, with branches to the Public Garden Portal and Pleasant Street Incline south of Boylston. Park Street, Scollay Square, and Haymarket stations were altered over the next two decades as transfers were added to the Cambridge - Dorchester Subway, East Boston Tunnel, and Main Line Elevated (now part of the Red, Blue, and Orange Lines, respectively). In 1962, the southern portal at Pleasant Street was closed; the following year, the northern half of the tunnel was substantially altered when Government Center and a new Boston City Hall replaced Scollay Square and Adams Square . The northbound tunnel to Haymarket station was rerouted; the southbound tunnel is still original . Scollay Square station was rebuilt as Government Center, and Adams Square station was closed . In 1971, the original Haymarket station was replaced with a new station just to the south . </P>

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