Updated

TRENTON, N.J. -- New Jersey Gov. Chris Christie on Thursday killed a decades-in-the-making train tunnel connecting New Jersey and Manhattan, saying the state can't afford to pay for cost overruns on the underway project.

Construction on the project began last year and was scheduled to be completed in 2018. The largest federal transportation project in the country, it was expected to double train traffic in and out of New York City during peak commute times.

But over the years, the cost for the tunnel has also nearly doubled as well.

It started at $5 billion in 2005 and grew to $8.7 billion by 2008. In recent months, Federal Transit Administrator Peter Rogoff has made public statements that put the price tag between $9 billion and $10 billion.

At a news conference Thursday, Christie said: "I can't put taxpayers on a never-ending hook."

New Jersey had committed $2.7 billion to the project. The federal government and Port Authority of New York and New Jersey had each pledged $3 billion.

A month ago, the Republican governor ordered a 30-day halt to all work on the tunnel over concerns that the project would go over budget.

Plans for the project had been in the works for about 20 years.

Currently, NJ Transit and Amtrak share a century-old two-track tunnel beneath the Hudson River. The new tunnel would add two more tracks, doubling the number of NJ Transit trains that could pass under the river.

Officials said it would create 6,000 construction jobs and add at least 40,000 new jobs after it is completed.

Christie's predecessor, Democratic Gov. Jon Corzine, broke ground on the tunnel in June 2009, a few months before the gubernatorial election that he lost to Christie.

During his campaign for governor last year, Christie supported the project.

But as soon as he announced the work stoppage, lawmakers and transportation officials suggested Christie had planned to scrap the project and to use the state's share of the money to pay for the nearly broke Transportation Trust Fund, which pays for local road projects and existing rail repairs.

Christie has refused to raise the state's gas tax, which is among the lowest in the country, to replenish the fund.

So far, about $600 million has been spent on the tunnel project. New Jersey could be on the hook to repay half of that to the federal government for breaking its commitment.

U.S. Sen. Frank Lautenberg, D-N.J., has said canceling the tunnel would violate an agreement with the feds in which New Jersey committed itself to the project in exchange for $3 billion in federal funding. He and other tunnel proponents planned to speak out on the governor's decision later Thursday.