On January 2, 1923, some off-peak trips were extended through the Boylston Street Subway to the surface station at ; all-day service began on October 10. Most trips were extended along the Beacon Street line to on December 14, 1929. The Washington Street service was cut back to Kenmore in June 1930 but resumed that September. On February 7, 1931, Commonwealth Avenue and Beacon Street service was extended from Park Street to Lechmere, and the existing shuttle services to Lechmere were replaced with Kenmore–Park Street shuttles.