 Earth excavation was conducted between walls once they were installed , and box structures were built using a bottom @-@ up construction method . Temporary decking constituted the top of the boxes , and the decking both braced the excavation and supported the walls and Second Avenue traffic . Of the below @-@ ground obstacles , Arup director of construction David Caiden stated : " It 's a spaghetti of tunnels , utilities , pipes and cables — I 've never seen anything like it . " Complicating the process , the project must go over , or under , subway lines , Amtrak railway lines , and the Queens @-@ Midtown Tunnel linking Manhattan and Queens , in later phases . 
