The 1947 state act that created the Metropolitan Transit Authority (MTA) from the Boston Elevated Railway established four immediate projects for the new agency, one of which was expansion of the Tremont Street subway to four tracks between Park Street and Scollay Square. As part of the plan, Park Street and Boylston stations were to be combined into a single Boston Common station, with a direct entrance from an underground parking garage. The garage ultimately opened in 1961, but the stations were not combined. The south headhouse on the northbound side was removed in 1963.