Previous work extending subway service through the upper level of the 63rd Street Tunnel to lines in Queens also extended the lower level to a point west of Northern Boulevard, across from the Sunnyside Yard. Work in Queens included extending the tunnel under Northern Boulevard and boring four tunnels under Sunnyside Yard. This was a particularly delicate and expensive task due to the existence of the elevated BMT Astoria Line and the underground IND Queens Boulevard Line directly above. In addition, the existing tunnel bell mouth west of Northern Boulevard was expanded to serve as the staging area for the Manhattan work, bringing in workers, equipment and supplies and bringing out the muck and debris from excavation. A temporary narrow-gauge railway and a conveyor belt system were constructed behind the tunnel boring machines and through the 63rd Street Tunnels to the Queens bell mouth. Due to its shape, the Queens work site was nicknamed the "Q-tip".