Legislators at the state Capitol are determining how we fund the remaining costs to complete Honolulu’s rail system. There are a number of options under consideration, and it is not clear which option they will select.

But what we do know — with certainty — is that if we do not complete the full 20-mile, 21-station system from East Kapolei to Ala Moana Center, Honolulu risks substantial increases in the cost of the $8.2 billion project.

That was made clear to us when we met in late February in Washington, D.C., with U.S. Federal Transit Administration (FTA) Executive Director Matthew Welbes and senior staff to discuss Honolulu’s rail project and the funding challenges it faces.

The officials told us that if funding for the remainder of the project is obtained, the $1.55 billion in promised federal financial support would be assured. That is the amount the federal government committed to in the Full Funding Grant Agreement (FFGA) with the City and County of Honolulu. But it was emphasized that federal financial support is contingent on building the planned system, all 20 miles and 21 stations.

Additionally, the FFGA clearly states that Honolulu risks losing future federal transportation dollars not just for rail, but other projects as well if we violate the contract. To remain compliant, we must build the rail line to Ala Moana.

That full system is better known as “Plan A.” It is the route that the FTA originally agreed to, and it is the route that officials are expecting Honolulu to complete.

The Honolulu Authority for Rapid Transportation (HART) is preparing a recovery plan for the FTA, which is due at the end of April.

The plan will offer details on a Plan B, which HART believes could possibly be built with our existing financial resources. While details of Plan B are being finalized, we do know that the rail line will stop far short of Ala Moana Center. There will be significantly fewer than the 21 planned stations, and undoubtedly far fewer people willing to park their cars and take the train.

Welbes and his senior staff made clear to us that if Honolulu chooses Plan B, the City will face significant challenges in regards to the commitment of federal funding for the project. These include:

>> First: the need for, at minimum, an environmental impact assessment, and more likely, a full supplemental environmental impact statement.

>> Second: if the scope of the project substantively changed, the FTA would need to renegotiate the terms of our FFGA. Among the items subject to renegotiation could be the federal contribution to the project, depending on the extent to which the project scope and intended transit benefits are changed.

Having to complete new environmental studies would delay the project and certainly increase costs. It would also likely allow project opponents to again file litigation, which would add further delays and costs. And renegotiating our FFGA opens up the possibility of the federal government reducing the level of its financial support.

We regret the situation in which we and our state colleagues find ourselves. That said, Plan A maintains compliance with our FFGA and ensures the highest level of ridership and mobility to allow for the transformation of Honolulu’s urban corridor for the benefit of our residents and visitors.

Ron Menor is chairman of the Honolulu City Council, and Ikaika Anderson, Council vice chairman, chairs the Transportation and Planning Committee.