passageway from the basement to the Rockefeller Center station. A similar passageway was built from the basement of 1285 Avenue of the Americas, one block north of the Time–Life Building. In February 1958, Rockefeller Center Inc. leased in the northern mezzanine for 20 years at a total cost of $2 million over that period. Architects Harrison & Abramovitz were hired to redesign the mezzanine with stores similar to Rockefeller Center's underground mall. The renovation of the mezzanine was completed in February 1960, along with the passageway to 1271 Avenue of the Americas. Workers installed about of asbestos floor tiles as part of the project, and they also installed white, gray, and black panels on the walls, ceilings, and columns. The bellmouths north of the Rockefeller Center station went unused until 1962, when the New York City Transit Authority (NYCTA) announced it would extend the Sixth Avenue Line to 57th Street as part of the Chrystie Street Connection. Construction of the spur cost $13.2 million. With the completion of express tracks between West Fourth and 34th Streets in 1967, the B and D trains started running express on the Sixth Avenue Line. The 57th Street station opened in 1968, upon which KK trains began serving the Rockefeller Center station. 1970s to present As part of the construction of 1211, 1221, and 1251 Avenue of the Americas in the early 1970s, passageways were constructed from the basements of each building to the Rockefeller Center station. The new passageways had been completed by 1974. The NYCTA installed turnstiles and stairways to accommodate the additional passenger traffic, and Rockefeller Center Inc. paid for the improvements. An entrance with glazed-brick walls was added at 48th Street. In addition, Rockefeller Center Inc. built a passageway between 47th and 49th Streets, running parallel to the station's mezzanine. The Metropolitan Transportation Authority (MTA) announced in 1990 that it would spend $730 million to renovate 74 subway stations, including the Rockefeller Center station. In 1994, amid a funding shortfall, the administration of mayor Rudy Giuliani proposed delaying the station's renovation. Later that year, the MTA announced it had indefinitely postponed plans for renovating the Rockefeller Center station. By the mid-2000s, the New York City Transit Riders Council had ranked the Rockefeller Center station as among the system's dirtiest subway stations. The group described the station as having leaky ceilings, litter, dirty walls and floors, and water on the floor.