A new report from the federal government puts the cost of building a new Hudson River rail tunnel and saving the old one at up to $13 billion—50% more than the estimated expense of a previously scuttled tunnel project.

Supporters remain confident that the project will be done, if only because it must: The existing two-track tunnel, which shuttles Amtrak riders and millions of New Jersey Transit commuters to and from Manhattan each year, is aging and in desperate need of major repair, which involves first building a new sibling conduit.

But the new draft environmental impact statement by the U.S Department of Transportation found the endeavor, part of a larger project known as Gateway, would run into the range of $11.7 to $12.98 billion. A similar tunnel construction and repair effort, part of the Access to the Region's Core project killed by Gov. Chris Christie, was priced at $8.7 billion. Christie had said he did not want New Jersey to be on the hook for cost overruns.

At a press conference unveiling the report at New York Penn Station Thursday morning, Gateway Program Development Corp. Interim Director John Porcari cited a figure of $12.9 billion—$11.2 billion for constructing the new shaft, $1.7 billion for overhauling the old. (Additional costs would stem from work to maintain the current operation before either of the two tracks under the river is closed for repairs.) He attributed the difference from earlier estimates to increased security, excavation and refurbishment costs, a consequence of a clearer and more accurate plan for both the construction and rehabilitation elements of the project.

"Those numbers are better known than they were before," he said. "The cost numbers will continue to be refined."

Porcari revealed that the analysis was completed Friday, the same day that the Department of Transportation formally withdrew its trustee from the development corporation. The entity had been formed in 2015 at the behest of now-Senate Minority Leader Charles Schumer, with a four-person leadership that also included Amtrak Chairman Anthony Coscia and two representatives from the Port Authority of New York and New Jersey, one picked by the governor of each state.

Some interpreted the withdrawal of the DOT trustee as an ill omen for the project, an undertaking which Schumer and the Obama administration steered through initial resistance from Christie and Gov. Andrew Cuomo. Others saw it as a play by President Donald Trump to pressure the Senate Democratic leader and to put Trump's own stamp on the project, as he advances a vision for infrastructure that involves private capital investment, tax credits and toll revenue.

Porcari, himself a former deputy secretary of transportation under President Barack Obama, appeared at pains to signal to the Trump administration that his group would aggressively investigate the possibility of seeking a private partner to help finance the tunnel's construction.

"We've always had a very open mind as to how best to build it," he said. "That's something we're actively evaluating."

He said the corporation would study the possibility of employing a public-private partnership model as part of an "industry forum" scheduled for this summer.

Nonetheless, he echoed Schumer's insistence that the project cannot proceed without substantial assistance from Washington. He noted that the Port Authority, Amtrak and New Jersey Transit have committed to covering half the overall cost of the venture, which before Thursday was estimated at $24 billion.

"It's really important to point out that any project of national significance like Gateway, which is literally a linchpin not just for the region's but the nation's economy, cannot move forward without a federal funding partner," he said, noting that 10% of the country's gross domestic product depends upon transit between New York and New Jersey. "It's the most urgent infrastructure project in America."

The revised estimate will push the total cost of Gateway, which also includes the replacement of the Portal Bridge in New Jersey and bringing both train tunnels to full rail capacity, into the neighborhood of $28 billion to $29 billion. Trump Transportation Secretary Elaine Chao has vowed the federal government will show no "prejudice or partiality in favor of these projects ahead of hundreds of other projects nationwide."