NEWARK, N.J. (AP) — Plans are moving ahead to build a new Hudson River rail tunnel and make other large-scale infrastructure improvements, but the lack of a final decision on the scope of the project is stalling further advances, the federal official overseeing the project said Thursday.

U.S. Transportation Secretary Anthony Foxx also characterized as “not crazy, but not easy either” a proposal by the governors of New Jersey and New York that the federal government pay for half of the estimated $15 billion project, with the states and the Port Authority of New York and New Jersey paying the rest.

Before that can happen, he said, a final plan must be agreed upon.

“I can’t give you a timeline on how quickly the region will come to consensus on what the project will be,” he said at a news conference at the Port Newark Container Terminal to discuss a new infrastructure grant program. “That’s step one. We’re going to have to all work hard to get the project scoped so we have a real cost to work with and then look from there at what programs we have available on the federal level and what the states can do.”

Roles have begun to be assigned among the various state and federal agencies on the Gateway project, Foxx said. The Federal Railroad Administration will take the lead within the Department of Transportation, New Jersey Transit is expected to be the project sponsor for an environmental review, and Amtrak — which owns the existing tunnels linking New York and New Jersey — will be the lead agency for preliminary engineering.

Fox added that NJ Transit has indicated that some of the engineering work performed for ARC, a previous tunnel project killed by Gov. Chris Christie in 2010 amid fears of cost overruns, can be used for Gateway, which could reduce costs.

Gateway, conceived by Amtrak after the ARC tunnel cancellation, would build a new tunnel to augment an existing century-old tunnel, which would then undergo extensive work to repair damage from Superstorm Sandy. It would also expand Penn Station in New York, replace a 105-year-old bridge in New Jersey and expand track capacity, among other improvements.

It isn’t known if any elements of the project may be pushed back or even shelved. Amtrak has estimated it would take roughly 10 years to finish a new tunnel, and longer to finish all the other elements.

“We’ve been developing the scope of the Gateway Program for several years now and are working with various parties to advance elements of it today,” Amtrak spokesman Craig Schulz said. “As a partnership among these various parties develops, we’ll further refine that scope to ensure it achieves our mutual goals.”

An NJ Transit spokeswoman said Thursday that the agency is in ongoing discussions with Amtrak about the Gateway project and is sharing information from the ARC project.

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