The Christie administration, which killed a trans-Hudson rail tunnel because of fears of cost overruns, will pay its "fair share" of a proposed Amtrak tunnel project linking New Jersey and New York City, Christie's transportation chief said Friday.

The payment would probably be a user fee to share the tunnels that Amtrak proposes as part of its $14.5 billion Gateway project, state transportation commissioner James Simpson said.

Simpson, in Voorhees to address the Chamber of Commerce of Southern New Jersey, declined to predict how much of the cost New Jersey would be willing to shoulder. He said he was meeting with Amtrak president Joseph Boardman and other officials to discuss cost-sharing.

Christie spokesman Michael Drewniak said Friday, "At this time, it would be quite premature to say what New Jersey would commit to in terms of dollars."

The Gateway project proposes to increase rail service on the Northeast Corridor by adding two tunnels under the Hudson, replacing the century-old Portal Bridge near Newark, and expanding Pennsylvania Station in New York.

The project, which Amtrak now says it hopes to complete by 2025, is a key part of Amtrak's effort to increase capacity on the overloaded Northeast Corridor.

It would increase NJ Transit commuter-rail capacity into New York to 33 trains per hour during peak hours, from the current 20.

And it is integral to Amtrak's long-term goal to build a new high-speed Northeast Corridor rail route that would allow trains to make the 426-mile trip between Boston and Washington in three hours and 23 minutes — compared with the current eight hours on Amtrak's Northeast Regional trains, or six hours and 37 minutes on Acela Express.

The Gateway project was unveiled early last year, about four months after Christie canceled another rail-tunnel project, the ARC (Access to the Region's Core) tunnel, citing its costs.

Christie killed the tunnel project in October 2010, after construction had started. He said then that the cost was likely to top $11??billion, and could exceed $14??billion, and that New Jersey would pay 70 ?percent of the bill.

A study by the federal Government Accountability Office, released last month, questioned Christie's conclusions, noting that the last estimate by the Federal Transit Administration was $9.8??billion to $12.4??billion and that no agreement was reached on paying for any cost overruns.

The Gateway project is still in the study phase, with financing uncertain. Last month, the U.S. Senate Appropriations Committee approved $20??million for Amtrak to continue preliminary design and engineering work on the proposal.

Simpson told the South Jersey business leaders that the Christie administration also remained committed to an 18-mile light-rail line between Glassboro and Camden. The long-proposed line is now the subject of an $8.1??million environmental assessment being conducted by the Delaware River Port Authority and paid for by NJ Transit.

Simpson said it remained unclear who would pay to build the $1.6??billion line or who would operate the trains if it were built.

"The feds are going to have to be our partners," Simpson said.

The line would run alongside an existing Conrail freight line through Glassboro, Pitman, Mantua, Wenonah, Woodbury, Deptford, West Deptford, Westville, Bellmawr, Brooklawn, Gloucester City, and Camden.

It would connect to PATCO and River Line trains at the Walter Rand Transportation Center in Camden, where passengers could catch trains to Philadelphia or Trenton.

Contact Paul Nussbaum at 215-854-4587 or