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Photo: Mike Rosenthal/New Jersey Transit

New Jersey Transit and the Port Authority of New York and New Jersey are looking to build a $7.6 billion tunnel under the Hudson River in order to accommodate rising passenger numbers on the New Jersey Transit train system. The new proposed tunnels will bring the total number of train tunnels beneath the Hudson to 4, doubling the number of tracks already in use today by New Jersey Transit trains.

This time, engineers will use an earth pressure balance machine to bore from New Jersey all the way to New York, and then switch to a hard rock machine to burrow under Manhattan.

The new tunnels will enter Manhattan between 28th and 29th Streets about 150 feet below ground to avoid a bulkhead at the river’s edge, the Hudson River Park and what is expected to become the extension of the No. 7 subway line that is supposed to run along 11th Avenue.

The tunnels will run northeast to 10th Avenue and split into lower and upper tunnels that will form a two-tiered cavern with six tracks under 34th Street. The station will extend from Eighth Avenue to Sixth Avenue, with a “tail” to Fifth Avenue for trains to park.

Construction of the two new tunnels, each about 4 miles in length, will approximately take 8 years.

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The New York Times has a cool interactive graphic showing how the tunnels under the Hudson River were built. Essentially, the idea behind tunnel boring machines remains the same while the technology has improved. The comparison of the 1900′s method and the “modern method” show how it has changed.