The Massachusetts Bay Transportation Authority (MBTA) took over from the MTA in 1964. The MBTA gave color designations to the four subway lines in 1965, with the Tremont Street subway routes designated as the Green Line. On December 26, 1964, Heath Street– short turns using the newly-opened loop at Government Center were added to accommodate ridership from the new Prudential Center.These trips were cut back to Park Street the next month, but returned to Government Center on March 25, 1967. On September 19, 1966, the Heath Street short turn was increased in frequency, with every other trip terminating at Heath Street during peak hours. This experiment was unsuccessful and was ended on November 7. The Heath Street short turns were reduced from two-car trains to single cars on January 3, 1972.