NORTH BERGEN, N.J. — Construction began today on the nation's largest transportation project, an $8.7 billion rail tunnel into New York City that is expected to reduce the time it takes commuters to reach Manhattan from New Jersey by an average of 40 minutes.

The 8.8 milelong fourth rail tunnel under the Hudson River will require the removal of 2 million cubic yards of rock and soil — roughly a third as much as the Hoover Dam — and will take eight years to build.

"This is an incredible project," New Jersey Gov. Jon Corzine told a crowd of 750 people at a ceremony today in northern New Jersey. "In today's economic recession, it has the added value of creating 6,000 new jobs day in and day out for the next six or seven years."

The new tunnel will speed the work commute from New Jersey to New York City by increasing the number of NJ Transit passenger trains passing under the river during peak rush hour from 23 to 48.

NJ Transit currently has only one two-rail tunnel, which it shares with Amtrak. The Path system, which operates commuter trains for the Port Authority of New York and New Jersey, has two rail tunnels, each with two rails.

The new tunnel will add two more rail lines. None of the tunnels transports rail cars carrying freight.

Federal Transit Administration chief Peter Rogoff said the federal government's $3 billion contribution to the project is the largest ever by his agency. The tunnel is expected to facilitate an exponential increase in direct routes, which will double NJ Transit's passenger capacity during the morning rush hour to 90,000 trips.