An innovative gantry system placing prefabricated bridge segments has enabled the first, $590-million phase of the Park Avenue Viaduct Replacement project in New York City to finish structural work this month. Over 19 weekends, crews performed 128 bridge installations equaling 8,240 track ft for the aging 132-year-old structure, all without disrupting Metro-North service. According to the New York Metropolitan Transportation Authority, the project as a whole is $93 million under budget and 51 months ahead of schedule.
The elevated concrete-and-steel structure carries four tracks and 98% of all Metro-North trains every day. Phase 1 kicked off in October 2023 to replace the full substructure and superstructure from East 115th Street to East 123rd Street along Park Avenue in upper Manhattan as well as the installation of new track, power, communications and signal systems.
Phase 1 completed 21 months ahead of its initial schedule. At the same time, crews with the design-build team led by Halmar International in March 2024 began working on Phase 2, from East 127th Street to mid-block between East 131st Street and East 132nd Street.
On each of the 19 weekends, structural supports were constructed underneath the existing viaduct. Then, two of the four tracks of the viaduct were taken out of service while train service continued on the other remaining tracks. Using the moveable gantry, crews cut and removed sections of the existing structure. The rest of the structure is supported on a temporary bracing system.
The new 190,000-lb prefabricated sections were brought in and attached to the new support structure, with pre-installed rail plinths, track fasteners, third rail fasteners, and walkway and railings.
The 200-ton-capacity gantries “are the biggest gantries ever produced by MiJack,” says Nick Altmeter, project manager with Halmar, which leads the design-build team building the job. AECOM serves as lead design consultant. The construction included 64 hammerhead caps and more than 700 16-in.-dia minipiles down an average of 40 ft into rock.
Crews are constrained by the dense urban environment, as sidewalks and crossings had to remain open during construction and street lamps had to be turned sideways. Additional work on the systems and track level will continue through the winter, with Phase 1 expected to reach substantial completion in April 2026. Phase 2 substantial completion is expected in September 2027.
