The planners of the $16 billion rail tunnel project known as Gateway said they passed the “point of no return” on Tuesday when the federal government told Congress that it would provide an additional $6.88 billion to the project.
The federal grant — the most ever provided to a mass-transit infrastructure project in the country — was the final piece of the funding puzzle for the long-delayed tunnel between New Jersey and Pennsylvania Station in Manhattan.
It gives planners of the sprawling project the green light to hire engineering and construction companies to start boring through a cliff in North Bergen, N.J., and under the Hudson River.
That work could begin as soon as this year and is scheduled to be completed in 2035, said Kris Kolluri, the chief executive of the Gateway Development Commission.
“This is the moment that has eluded this region for literally almost 30 years,” Mr. Kolluri said. “We are essentially at the point of no return.”
The Gateway project is the second attempt at building an additional rail tunnel to increase capacity and improve the reliability of train service between New York and points west and south. The existing pair of single-track tunnels is more than 110 years old and suffering from damage sustained by flooding during Hurricane Sandy in 2012.
In 2010, work had begun to make way for a different rail tunnel under the Hudson that was known as Access to the Region’s Core, or ARC. But before signing a similar funding agreement with the federal Department of Transportation, Chris Christie, the Republican governor of New Jersey at the time, canceled the project and returned some money to Washington.
The unilateral decision last week by Kathy Hochul, the Democratic governor of New York, not to go forward with a plan to charge tolls for driving in Manhattan’s business district reminded some transportation experts of that abrupt move by Mr. Christie.
“I’m a happy man today,” said Senator Chuck Schumer, the Democratic majority leader from New York and the Gateway project’s biggest champion in Washington. “Barring some major, major, act-of-God catastrophe, it’s all systems go.”
The federal government had pledged the $6.88 billion toward Gateway last year, but a detailed funding agreement that will include about $600 million annually in the federal budget had to be worked out. On Tuesday, Veronica Vanterpool, the acting administrator of the Federal Transit Administration, notified leaders in Congress that the administration intended to sign that agreement with Gateway in about two weeks.
Mr. Schumer said that the grant would increase the federal funding for the Gateway project to about $12 billion, about 70 percent of its estimated total cost. That total includes about $1 billion from Amtrak, which owns the existing tunnels and Penn Station.
The balance, along with any overruns, will be supplied by New York and New Jersey, Mr. Schumer said.
Philip D. Murphy, the Democratic governor of New Jersey, said he thought Mr. Christie’s stated concern about New Jersey shouldering cost overruns for ARC was “overblown.”
He added that he thought his state was “in a good place in terms of exposure” to any unexpected costs of Gateway because of the teamwork demonstrated by New York state and city officials, as well as Amtrak and the Port Authority of New York and New Jersey.
“This is a big win for both sides of the Hudson,” the governor said.
Last week, the two states and the Port Authority received approval to borrow their shares of the project’s cost from the federal government. That is a standard practice for major infrastructure projects that was opposed by the White House when Donald J. Trump was president, Mr. Schumer said.
“Trump put many roadblocks in the way of Gateway,” Mr. Schumer said. “He held it up for all four years that he was president.”
Mr. Trump’s successor, Joseph R. Biden Jr., was a regular rider of Amtrak trains when he was a senator and has been a strong supporter of the Gateway project.
“The next thing we now have to do is execute, and execution isn’t easy,” said Anthony R. Coscia, the chairman of Amtrak and vice chair of the Gateway Development Commission. “We’re just getting started, but when we’re done, people who live in places now where the train service is terrible are going to have really efficient train service.”