Several years after it was inaugurated in 1959, the Riverside Line was extended to Lechmere at most times. The MBTA took over transit operations in 1964. With the ability to reverse Green Line trains at Park Street, Government Center, North Station, and Lechmere, the MBTA frequently switched which lines ran to which downtown terminals to match passenger demands and other operational needs. On September 10, 1966, the remaining Commonwealth Avenue line service to Lechmere was cut back to Park Street. In 1967, the MBTA redesignated the remaining streetcar operations as the Green Line with branches "A" through "E". The Commonwealth Avenue line became the B branch, the Beacon Street line the C branch, and the Riverside line the D branch. After March 25, 1967, the "C" and "D" branches served Lechmere at all times.