Tremont Street Subway is incapable of serving Park Street station.
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 -LRB- after the City and South London Railway in 1890 , and the Budapest Metro 's Line 1 in 1896 -RRB- , opening on September 1 , 1897 .. MBTA Subway. MBTA Subway. electric traction. electric traction. City and South London Railway. City and South London Railway. It was originally built to get streetcar lines off the traffic-clogged streets , instead of as a true rapid transit line .. rapid transit. rapid transit. It now forms the central part of the Green Line , connecting Boylston Street to Park Street and Government Center stations .. Green Line. Green Line ( MBTA ). Boylston Street. Boylston ( MBTA station ). Park Street. Park Street ( MBTA station ). Government Center. Government Center ( MBTA station ). Boylston. Boylston ( MBTA station ). 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 .. Pleasant Street Incline. Pleasant Street Incline. Park Street. Park Street ( MBTA station ). Boylston. Boylston ( MBTA station ). Scollay Square. Scollay Square ( BERy station ). Adams Square. Adams Square ( BERy station ). Haymarket. Haymarket ( MBTA station ). Public Garden Portal. Green Line ( MBTA )#Public Garden and Boylston Street. 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 -LRB- now part of the Red , Blue , and Orange Lines , respectively -RRB- .. Park Street. Park Street ( MBTA station ). Scollay Square. Scollay Square ( BERy station ). Haymarket. Haymarket ( MBTA station ). Cambridge-Dorchester Subway. Cambridge-Dorchester Subway. East Boston Tunnel. East Boston Tunnel. Main Line Elevated. Main Line Elevated. Red. Red Line ( MBTA ). Blue. Blue Line ( MBTA ). 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 .. Government Center. Government Center ( MBTA station ). Scollay Square. Scollay Square ( BERy station ). Adams Square. Adams Square ( BERy station ). Boston City Hall. Boston City Hall. The northbound tunnel to Haymarket station was rerouted ; the southbound tunnel is still original .. Haymarket. Haymarket ( MBTA station ). Scollay Square station was rebuilt as Government Center , and Adams Square station was closed .. Government Center. Government Center ( MBTA station ). Scollay Square. Scollay Square ( BERy station ). Adams Square. Adams Square ( BERy station ). In 1971 , the original Haymarket station was replaced with a new station just to the south .. Haymarket. Haymarket ( MBTA station )