existing Scollay Square station. The upper part of the former station was later converted to storage space. Scollay Under opened on March 18, 1916, an island platform with staircases to Scollay station. The 1898-built main platform was extended during the project to accommodate expected loads of transferring passengers. On April 18, 1924, the East Boston Tunnel including Scollay Under was converted from low-platform streetcars to high-platform third-rail-powered rapid transit. A portion of the low streetcar platform remained east of the new high platform. The northbound (Cornhill Street) entrance was closed on November 24, 1917, forcing all passengers to use the southbound Tremont Row entrance. In 1927, the original headhouse was replaced with a simple staircase to improve sightlines for auto drivers. The station was further renovated in 1928 with new lights, and improved fare collection equipment. Eastern Massachusetts Street Railway service to Brattle Loop ended on January 13, 1935, though some BERy streetcars continued to use it. The Metropolitan Transit Authority (MTA) replaced the BERy in 1947 and continued to reduce streetcar services. The last Brattle Loop service was discontinued in 1952. The northbound platform was extended over the loop in 1954 to allow two 3-car trains of PCC streetcars to board simultaneously. Government Center Boston City Hall Plaza replaced Scollay Square in the early 1960s. Scollay Square station was wholly renovated, and the northbound tunnel was realigned to accommodate the foundation of Boston City Hall. The work drastically altered the shape of Brattle Loop and provided a new northbound-to-southbound turnback loop. The stairways to the lower level were relocated, and a fare lobby was built in a low brick structure at the surface. The 1963-built headhouse was often described as resembling a bunker or a cave, even by MBTA management. Government Center station was dedicated on October 28, 1963, though the new loop was not activated until November 18, 1964, when the Commonwealth Avenue line was extended from Park Street to Government Center. Despite the new name, several tiles mosaics reading "Scollay Under" and "S" were still extant and gradually uncovered over the years. On August 26, 1965, as part of a wholesale rebranding of the system, the MBTA (formed in 1964 to replace the MTA) designated the remaining streetcar routes as the Green Line and the East Boston Tunnel line as the Blue Line. In 1968-69, a "Phase I" modernization added false ceilings, fluorescent lights, and other aesthetic