 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.
