The New York and New Jersey governors offered back in September to pay half of the cost of a new train tunnel under the Hudson River. But it wasn't until Wednesday's announcement of a new entity to construct the project that the public got any sense what the feds would be willing to contribute.

The answer: half, or roughly $10 billion of the potential $20 billion that's needed for the project. 

"It was a long struggle but getting all the parties on the same page is a very big first step," New York Sen. Charles Schumer said in a statement. "We will scour every part of the federal government to get our 50 percent and we know the states will do the same.”

According to officials, the new governance entity follows the framework laid out by Schumer earlier this summer. It will be called the Gateway Development Corporation and will be housed within the Port Authority and controlled by a four-member board with representatives from New York, New Jersey, Amtrak and the federal government. 

The existing trans-Hudson rail tunnel is more than 100 years old and in dire need of repair. But Amtrak, which owns the tunnel, says it doesn't want to take it out of service until a new one is built.

The Gateway project would double existing rail capacity by adding two tubes. Its $20 billion pricetag also includes the replacement of aging rail infrastructure that creates bottlenecks in New Jersey (Portal Bridge, we're talking to you). The project would also beef up capacity at the Frank Lautenberg-Secaucus Junction and expand Penn Station.

"It’s a big day," Amtrak spokesman Craig Schulz said. "Everybody is now on board, we have a program. We have a project. Up till now it’s been proposals and conceptual. This is real, this is making it real, and that’s significant."

But many questions remain about the project, especially who will pay for cost overruns — a concern that New Jersey Gov. Chris Christie cited in his 2010 decision to cancel the ARC tunnel, the precursor to Gateway. Nor is there any timeline yet for when the tunnel might be built.