A subway for the Huntington Avenue line was proposed as early as 1906 to remove streetcars from congested Boylston Street and Copley Square. (Streetcars operated in mixed traffic on those segments, with a dedicated median only on Huntington Avenue west of Dartmouth Street.) A subway as far as Mechanics Hall was proposed in 1911, but it was rejected in 1912 on the grounds that the opening of the Cambridge subway and the Boylston Street subway would halve the number of streetcars on Boylston Street.