Tremont Street Subway

The Tremont Street Subway is a tunnel in Boston's subway system, and is the oldest subway tunnel in North America, opening on September 1, 1897. It was originally built as a tunnel to get streetcar lines off the streets, rather than a rapid transit line. It now forms the central part of the Green Line, connecting the Boylston Street station to Park Street and Government Center.

The tunnel originally served stations at Boylston Street, Park Street, Scollay Square, and Adams Square. The latter two stations were substantially altered when Government Center and City Hall replaced Scollay Square and Adams Square in 1963. Adams Square was closed altogether, and Scollay Square station was completely renovated and altered, and the northbound tunnel to Haymarket was rerouted, though the southbound tunnel is still original.