Tremont Street Subway is a tunnel.
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 . 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 . 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 .