Developer D.R. Horton convinced the state Department of Transportation that road improvements will mitigate traffic from 11,750 homes it wants to build in Ewa. But University of Hawaii traffic engineering specialist Panos Prevedouros trashed that notion Friday at a state Land Use Commission hearing.

Prevedouros told commissioners that Horton’s traffic analysis and DOT’s acceptance of mitigation plans are worthless, and he said drivers on the H-1 freeway might spend an extra 20 to 30 minutes in traffic if Horton builds the community called Ho‘opili.

"You will have a tremendous traffic impact," he said.

Prevedouros is one of roughly 20 expert witnesses testifying for three entities — the Sierra Club’s Hawaii chapter, community group Friends of Maka­kilo and state Sen. Clayton Hee — that are trying to convince the commission to reject Horton’s plan to convert 1,554 acres of prime farmland for urban development.

Eight witnesses expressed their views Thursday mostly about negative impacts on agriculture in an attempt to counter endorsements for Ho‘opili from the Hawaii Farm Bureau Federation, the state Department of Agriculture and farm tenants operating on the site.

Traffic is another major issue in the case.

Horton’s projected traffic impacts for Ho‘opili led DOT to withhold support of the project three years ago. But the developer has since offered to pay for adding one lane to H-1 in each direction between the Kunia and Waiawa interchanges.

Alvin Takeshita, DOT’s highway division administrator, told the commission in January that the new lanes, plus improvements planned by the state — mainly an afternoon H-1 contra-flow lane and widening H-1 between Punahou and Middle streets — will sufficiently mitigate Ho‘opili impacts.

Prevedouros, however, said these improvements don’t address the bottleneck, or choke point, where H-1 merges with H-2 about four miles Diamond Head of the Ho‘opili site.

"This is a fatal flaw," he testified. "A choker is a choker is a choker is a choker."

Prevedouros said the proposed lane widenings will amount to little more than "a paint job on the freeway" that doesn’t benefit people commuting between Leeward Oahu and town.

The engineering professor also criticized a traffic impact analysis by a Horton consultant that projects vehicle trips and congestion. The report provides projections for 2020 assuming completion of one-third of Ho‘opili. An updated report assuming full build-out is being prepared but isn’t required by DOT before the Land Use Commission votes.

Prevedouros said the report belongs in the trash and that the commission shouldn’t rely on it for making a decision.

Benjamin Kudo, an attorney representing Horton’s local Schuler Division, challenged the accuracy of the 20- to 30-minute traffic impact Prevedouros suggested would result on H-1 from Ho‘opili. Prevedouros called his projection a "casual guesstimate" and acknowledged that he hasn’t done an empirical study.

Kudo also explored how Prevedouros’ stance against the city’s planned rail system, which is designed to make two stops on the Ho‘opili site, might be influencing his testimony against Horton’s project.

Prevedouros unsuccessfully ran for mayor in 2008 and 2010 as the only anti-rail candidate, and is still involved in efforts to stop the rail project.

Prevedouros said he opposes rail but not housing development. He said the only effective traffic mitigation for Ho‘opili would be adding lanes to H-1 running between the project and University Avenue.

Friends of Makakilo, led by Kioni Dudley, who also opposes rail, presented Prevedouros as a witness.

The only other witness to testify Friday was William Tam, head of the state Commission on Water Resource Management. Sen. Hee subpoenaed Tam to testify. Tam raised concerns that models to predict water availability are outdated, but he refrained from saying whether he thought enough water exists for Ho‘opili.

A Horton consultant and a Board of Water Supply official testified previously that plenty of water is available. The Water Resource Commission will consider whether to allocate water for Ho‘opili if the project is approved.

The next hearing with more witnesses for Ho‘opili’s challengers is tentatively scheduled for March 15.