Transporting more than 8.5 million people in the city that never sleeps is a challenge. The 24 subway lines operated by the Metropolitan Transportation Authority (MTA) are frequently congested during morning and evening rush hours. Commuters living on Manhattan’s East Side lacked a direct subway line, resulting in a surplus of riders on the Lexington Avenue Subway’s 4, 5 and 6 trains, which in turn caused delays and safety risks in bottlenecked stations.
In an effort to relieve excessive crowding and stress on the entire system’s infrastructure, MTA commissioned the AECOM-Arup Joint Venture (AAJV) as the prime engineering and design consultant for the new Second Avenue Subway (SAS) — the first major expansion of the New York City Transit (NYCT) subway system in over 50 years.
SAS’s first-phase expansion runs 1.8 miles between 63rd and 96th streets and consists of three new stations at 72nd, 86th and 96th streets, plus one upgraded station at 63rd Street. Completion of this project required a comprehensive approach that extended beyond conventional engineering, with an eye toward devising new standards for underground tunneling and station design. Among our innovative solutions:
Tunneling: A tunnel boring machine (TBM) weighing 485 tons and measuring 450 feet long was used to excavate 12,800 feet of twin-track tunnels measuring just over 22 feet in diameter. The three new stations rank among the largest underground excavations in North America, at nearly 64 feet wide, 100 feet deep and 1,600 feet long. The tunnel’s concrete liners were the first in New York City not to use steel-reinforcing bars, instead using steel fibers for flexural reinforcing and crack control, and polypropylene fibers for prevention of explosive spalling in the event of a tunnel fire.
Structural and geotechnical: Tying a brand new subway line into an existing, 100-year-old system is a Herculean endeavor, especially since this line sits below some of the world’s most congested infrastructure and ground conditions can vary from the hard rock of Manhattan schist to the soft soils of old river beds and swamps. One challenge involved an area of fractured, weathered rock at the start of the east tunnel that was not discovered despite numerous borings. Ground freezing was determined as the best approach to allow hard-rock TBMs to safely pass through, a decision that necessitated adjustments in tunnel sequencing but still kept the project on track.
Acoustics: Working with recordings taken at existing subway stations, acousticians used Sound Lab technology to create digital models and assess the best ways to reduce subway noises. Solutions included joint-free running rails with concrete ties encased in rubber, ceilings lined with perforated metal panels backed with sound-absorbing fiberglass, and public-address speakers placed strategically to optimize intelligibility.
Social: SAS sets a new standard for the city’s subway system. Stations are safe and welcoming, with high ceilings, column-free public spaces, Wi-Fi access and added security measures. Each station now has street entrances with escalators and ADA-accessible elevators — features much appreciated by riders who long endured stairway-only access. Energy-efficient lighting and graphical signage aid passenger orientation and reinforce station identity, which is further established through one-of-a-kind art installations anchoring each station. These monumental works of art, commissioned specifically for this project, collectively make SAS the largest permanent public art display in the state.
Opened to passengers on January 1, 2017, this US$4.45-billion project was completed on time and within the targeted budget, a major accomplishment given the scope and size. An intricate balance of infrastructure, buildings and transit, SAS is delivering on its promise to provide significant benefits across the entire transportation network by increasing accessibility with a one-seat ride to destinations throughout Manhattan, while reducing congestion on the nearby Lexington Avenue line by some 40-percent during peak morning hours. Average weekday ridership on SAS reached 176,000 passengers in just five months, proving this project is more than better transit — it’s better living.
Major Awards and Accolades: