Study Gives Edge to Clean-Diesel Buses; Metro Board to Purchase More Costly Natural-Gas Vehicles to Clear the air.(METROPOLITAN)

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A new study says the $94.5 million that Metro has spent on "environmentally friendly" natural-gas buses would have been better spent on diesel buses that operate just as cleanly - and cost about half as much.

The District is under a mandate from the Environmental Protection Agency to clean up the region's air by 2005 or face transportation funding cuts, said Metro board Chairman Chris Zimmerman. The Washington Metropolitan Transit Authority board, according to a statement released by Mr. Zimmerman, bought the 250 buses that used compressed natural gas as part of its anti-pollution efforts.

"There have been lots of studies, and I don't think there is any question that natural gas outperforms clean diesel over the long haul," said Mr. Zimmerman, Arlington Democrat.

He said natural-gas buses are cleaner and quieter than diesel.

But at least one board member disagreed with Mr. Zimmerman's assessment.

"I think, unfortunately, the symbolism of the natural-gas buses carries more weight than their actual effectiveness in cutting down on smog-producing emissions," said Dana Kauffman, Fairfax Democrat and the only dissenting vote on the Metro board for diesel over natural gas.

The day the Metro board decided to purchase more natural-gas buses, the California Air Resources Board (CARB) released a study showing that clean-diesel buses performed better than natural-gas buses in all but one category - the production of nitrogen oxide gases.

"The diesel bus equipped with a particulate filter ... produced lower emissions than either the [normal] diesel and the natural gas 'baseline' buses," the study said.

But the filtered-diesel bus produced more nitrogen dioxide emissions - the chemical most attributed to increasing smog. Manufacturers of the clean-diesel engines say those emissions can be reduced.

Jerry Martin, a CARB spokesman, said it is fair to say the clean-diesel outperforms the natural-gas bus. …