Proponents of alternatives to rail transit yesterday released a study contending that Honolulu's planned elevated commuter rail isn't as "green" as advertised.

The report, by St. Louis-based Demographia, contends that the city's $5.5 billion train will either slightly decrease greenhouse gas emissions or will, more likely, increase air pollution.

Those findings run counter to the city's contention that modern rail is more energy-efficient and environmentally friendly than alternatives such as elevated highway lanes.

Whether rail is more energy-efficient and reduces air pollution hinges on factors such as ridership and the fuel used to generate electricity.

According to the report, rail reduces greenhouse gas emissions only if the state massively reduces its reliance on fossil fuels used to power the train.

Demographia is run by Wendell Cox, an urban policy consultant and advocate for rail alternatives. Cox was not in Honolulu yesterday when University of Hawai'i engineering professor Panos Prevedouros presented the findings of the report at a news conference at Honolulu Hale.

The report estimated the air pollution generated by Honolulu's East Kapolei to Ala Moana rail line under various scenarios. Rail reduced air pollution only under a cost-prohibitive scenario in which the state relied on fossil fuel alteratives for 70 percent of its energy needs, according to the study.

The state currently relies on fossil fuels for most energy needs.

"They keep saying this project is green — rail is green," Prevedouros said. "Nothing could be further from the truth."

A rail alternative such as new managed highway lanes would reduce air pollution by reducing traffic congestion more than rail, Prevedouros said.

"You have to select alternatives that reduce congestion," he said. Tolled traffic lanes "correctly done reduce traffic by 30 percent — you will get a proportionate reduction in pollution automatically."

The Demographia report cost $5,000 and was paid for by the Small Business Hawaii Education Foundation.

City Managing Director Kirk Caldwell criticized the report as biased and insubstantial.

The city's Alternatives Analysis report released in 2006 estimated that regional emissions of greenhouse gasses would range from 0 percent to 4 percent less with the proposed rail system or an expanded bus service. That compares with a 0 percent to 4 percent increase in emissions for managed traffic lanes, according to the study by New York-based transportation engineering firm Parsons Brinckerhoff.

Even if Honolulu builds a train, traffic congestion on O'ahu will get worse. However, the city estimates that the rail system will pull about 30,000 autos off Honolulu roads in 2030.

Rail opponents "are saying that taking 30,000 cars off the road is not good for the environment," Caldwell said. "That just doesn't make common sense. That's going to have a huge, significant impact on pollution that is emitted by cars.

"The only other alternative choice would be to build more roads and highways , which are very polluting (and) they heat up the environment and only encourage even more cars."