Rock tunnels for the Second Avenue Subway

The Second Avenue Subway (SAS) will be a new line extending approximately 8.5 miles along Manhattan's East Side from 125th Street in the Upper Manhattan to Hanover Square Lower Manhattan. This subway line will have 16 new stations providing transfers to existing Metro-North commuter rail service and to New York City Transit subway lines and bus services. This paper discusses the central rock tunnels, which comprise approximately half of the subway route, and the constraints that resulted in the final alignment selection. These include the challenges of interfacing with the existing structures, subway lines and obstructions. It also discusses the philosophy adopted for estimating during preliminary engineering, the phasing of the project and introduces the scope of the first construction contract.