Diverting Honolulu’s planned elevated commuter rail line to avoid interfering with air traffic at Honolulu Airport could cost the city $65 million.

Moving a portion of the rail line to Ualena Street from Aolele Street was the least expensive option for the city, according to an April 7 memorandum from the Federal Aviation Administration to the Federal Transit Administration that was released to the Star-Advertiser in response to a Freedom of Information Request. Other options ran as high as $300 million, the memo said.

The city was forced to alter the rail route earlier this year because it encroached on runway airspace near the intersection of Aolele Street and Lagoon Drive. The track and a station near that intersection would have been at least four stories tall and about 1,300 feet from airport runways. That was within an airspace buffer designed to keep buildings and other obstructions from affecting airplane operations.

The added costs of resolving the airport issue were included in the project’s total price tag of $5.5 billion, which was the cost estimate given in a final environmental impact statement released Monday.

According to the FAA memo, the Ualena Street route was the cheapest of five alternatives studied. Leaving the route on Aolele and moving the runways back would have cost between $102 million and $128 million. Running the track along the median of the H-1 viaduct would have cost an estimated $300 million. Moving the track to Koapaka Street would have added about $95 million, while a "Makai H-1" option carried a $124 million price tag.

"Fortunately, the most expeditious option was also the cheapest option," City Council Chairman Todd Apo said. "It seems that made the choice as to which direction to go much easier to make."

City Transportation Director Wayne Yoshioka said yesterday that the estimates given in the April 7 memo are outdated and have since been cut by more than half. The added cost of altering the airport route is now estimated to be $29 million, Yoshioka said.

"We think those costs can be easily absorbed within the contingency (fund), which is $1.3 billion," he said.

According to documents released earlier by the state, the city was warned as early as 2006 about height restrictions near airport runways. However, it wasn’t until mid-2009 that it became clear that the city’s planned route encroached on a runway protection zone, the city has said.

On April 8, Mayor Mufi Hannemann announced that the train’s route would be shifted because moving the runways would be too expensive for the city. At the time, the city did not disclose the costs of the change but said they would be absorbed within the project budget.