On the Queens side, work 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. 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. An $83 million cut structure was built, which extends the tracks under Northern Boulevard into the Sunnyside Yard, and then was covered with a deck. In September 2009, the MTA awarded Granite-Traylor-Frontiere Joint Venture a $659.2 million contract to employ two 500-ton slurry tunnel boring machines to create the tunnels connecting the LIRR Main Line and the Port Washington Branch to the 63rd Street Tunnel under 41st Avenue. The four tunnels, with precast concrete liners, total in length. The two tunnel boring machines began digging on the Queens side in April 2011. On December 22, 2011, breakthrough was achieved in Tunnel "A" of the four Queens tunnel drives from the 63rd Street Tunnel bellmouth. By July 25, 2012, all four Queens tunnel drives were complete.