Honolulu has formally asked the feds to allow heavy construction on the rail project. And if it doesn’t get the green light soon, delay costs will start piling up.

Read Honolulu to Feds: OK Rail Work Or Costs Rise $100M for the details.

The letter — sent to the FTA Dec. 27 and attached to a memo to Honolulu City Council Vice Chair Ikaika Anderson two days later — includes HART’s rationale for why it needs a second LONP green light now and can’t wait for a Full Funding Grant Agreement in the fall.

“The consequences of LONP 2 not being approved will have serious impacts to the overall project budget, and in particular, poses the most significant impact on the project contingency,” Hamayasu wrote in the request to FTA Regional Administrator Leslie Rogers. “HART analysis indicates that the total delay impact could be at least $110.2 million if LONP 2 is not authorized in January 2012.”