As the west part of the Back Bay was filled, Huntington Avenue became a major thoroughfare. The Metropolitan received rights to construct a double-track line on Huntington from Copley Square (where it connected to the existing Marlborough Street line) to West Chester Park (later renamed Massachusetts Avenue) on March 18, 1881. The line opened by that September, serving the exhibitions at the Mechanics Hall and New England Fair Building. A extension along the newly-laid-out section of Huntington from West Chester Park to Brigham Circle was granted on October 29, 1883; its opening on October 1, 1884 completed a second Brookline–Boston route. A branch along Longwood Avenue to opened around late 1884. Around 1888, a branch was opened west from Brookline Village on Boylston Street and Cypress Street, serving the Pill Hill area. (This may have been to compete with the Boston and Albany Railroad, which had begun its Newton Circuit service through Brookline in 1886.)