When the original train tunnel beneath the Hudson River connecting Manhattan to New Jersey was built more than a century ago, workers toiled with picks and shovels from each side until eventually meeting in the middle.

A new tunnel, one of the largest U.S. mass transit projects in generations and which is expected to cost $16 billion, will take a decidedly modern approach.

Giant drilling machines nearly the length of two football fields armed with cutters harder than diamonds will chew through dense rock. A crew of about 40 will oversee a conveyor system hauling out debris as well as equipment to install the tunnel's curved concrete lining.

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The machines are expected to take about a year to grind through the first section in the New Jersey Palisades, which is made of tough volcanic rock, once digging starts later this year, according to Starace.
That's about 30 feet of tunnel a day. Other machines will dig under the riverbed.

In full, the new tunnel with two train tracks inside will run almost 2.5 miles (4 kilometers). The original two-tracked tunnel, damaged by saltwater during Superstorm Sandy, will be renovated.