PROVIDENCE, R.I. — Rhode Island transportation officials and Amtrak have been discussing ways to add service to T.F. Green Airport, they said on Thursday.

Rhode Island Department of Transportation Director Peter Alviti told WPRO-AM that his agency did a study with Amtrak about adding airport service and he believes it's doable in the next few years, but it could cost more than $100 million.

The addition would expand Amtrak service in Rhode Island while also providing an alternate way for people around the region to get to the airport in Warwick, a few miles south of Providence. Currently, only the commuter rail to Boston stops at the airport. Amtrak has just three stops in Rhode Island, in Providence, South Kingstown and Westerly.

Amtrak said in a statement later Thursday that it's too early to make any commitments regarding future service but confirmed the study had been conducted, and outlined the next steps, which include further analysis of the costs and infrastructure needs.

The feasibility study was recently completed by Amtrak, RIDOT and the Federal Railroad Administration to comply with a federal statutory requirement, Tom Moritz, Amtrak Assistant Vice President of Infrastructure Access and Investment, said in a written statement Thursday.

He said the next phase is to analyze the infrastructure needs and estimate how much it would cost.

"While it is too early in the planning process for any party to make commitments regarding future service or the construction of required improvements, Amtrak and RIDOT are continuing to work closely to further explore opportunities to enhance the transportation options of the citizens of Rhode Island and of the region," Moritz said.

The agency and Amtrak met Tuesday and agreed to move forward with one of four scenarios laid out in the study, which involves adding a stop at T.F. Green to the existing Amtrak Northeast Regional service, said RIDOT spokesman Charles St. Martin.

Ridership under the scenario was estimated at about 300,000 trips per year, he said. No exact timetable has been set, but an engineering study could start late next year, St. Martin added.

"The earliest likely outcome for beginning any construction is about four years from now," he said.

Amtrak service to the airport was envisioned when the station was built, and they provided for the service in the station's design and by getting certain permits to allow for an expansion, St. Martin said.