Opportunity
The Long Island Rail Road (LIRR) is the biggest commuter railroad system in the country, connecting commuters from Penn Station in Manhattan to Montauk, more than a hundred miles away at the eastern tip of Long Island.
But with 272,000 passengers every 24 hours, the system was straining its boundaries. Overcrowding was common on the LIRR, and nearly half of the riders who ended their journey at Penn Station had to walk a considerable distance or take another form of transportation to get to work.
Solution
The LIRR East Side Access project was designed to alleviate congestion and offer easier access to Manhattan by creating a railway link between Queens and Grand Central Terminal.
As tunnel consultant to the Program Management team, Mott MacDonald provided essential tunneling expertise, including design review and expert advice on tunnel design and construction:
- Tunnel lining
- Ventilation systems
- Fire/life safety issues
- Assessment of tunneling methods
The technical difficulties were daunting. New rail lines would run from the Harold Interlocking yard in Queens, already the busiest railroad interchange in the country. Tunnel portals under the Sunnyside Rail Yard would connect to the partially completed 63rd Street tunnel, running under the East River. The existing tunnel would be extended about one mile through glacial tills and fill, with boulders and high groundwater levels expected.
On the Manhattan side, twin tunnels were driven under Park Avenue, through hard micaceous schist that is subject to rock bursts (popping). Abrasive conditions and very hard intrusions made the job tougher.
In all, about 7 miles (11 kilometers) of new tunnel were driven beneath Queens and Manhattan. The diameter of each tunnel was about 22 feet (6.7 meters), with some tunnels circular and others arched. About 17,500 feet or more than three miles (5.3 kilometers) of previously constructed tunnels were rehabilitated as part of this enormous project.
Special tunnel boring machines were needed to handle the soft ground in Queens, with precast concrete segments installed as the machine advances. In Manhattan, two customized TBMs bore through the hard Manhattan schist, with steel rings and other rock supports installed so that mining could continue without interruption.
Finally, two caverns were mined under Grand Central Terminal to create a second major terminal consistent with the classic architecture of Grand Central. This was the biggest passenger terminal to be built in the US since the 1930s. Each of eight platform tracks would accommodate 12-car LIRR trains.
Outcome
The East Side Access project was completed in January 2023, easing crowding at Penn Station by diverting about half the LIRR commuters to Grand Central.
Commuters from Queens and Long Island now save 30 to 40 minutes a day in travel. Car travel has been reduced by an estimated 500,000 miles per day, reducing air pollution and the emission of greenhouse gases.
In addition to thousands of construction jobs, the project is expected to have positive and long-lasting economic benefits. An easier, more pleasant commute, coupled with easier access to midtown Manhattan, will support business growth in Manhattan and the greater New York City area.