SACRAMENTO, Calif. -- The Caifornia Air Resources Board will vote in March whether to repeal the current diesel-bus option and require state transit agencies to buy only natural gas and other alternate-fuel buses, venturing yet again into the sticky issue of diesel vs. natural gas.

The question is similar to one that Southern California's South Coast Air Quality Management District (SCAQMD ) answered last year by forcing schools to purchase alternative-fueled vehicles, typically natural gas, when adding or replacing buses. Many in the school transportation industry argued for the agency to preserve the choice of clean diesel (so-called "Green Diesel") or natural gas busses. But the agency decided, largely based on a now-debunked National Resources Defense Council report that said diesel exhaust was a cancer risk for children, to require natural gas.

The California Air Resources Board almost followed suit last year. The board considered banning diesel buses in favor of cleaner-burning natural gas - and ultimately hydrogen fuel cells - but, unlike SCAQMD, lobbying from transit operators and engine manufacturers persuaded the board to give transit agencies the choice of which bus type to purchase.

Some operators complained that converting to natural gas only to have to convert later to hydrogen was a waste of money. Natural-gas buses cost $40,000 more than a $280,000 diesel bus. Others argued that cleaner-burning diesel fuel and more efficient diesel engines could be developed that would reduce harmful emissions.

A compromised was reached wherein the board allowed diesel buses to live, but required agencies to create plans outlining how they eventually will curb diesel pollution.

The compromise has come to be known as the "Bay Area Exemption," as the San Francisco-Oakland vicinity is among the few regions where transit agencies have not elected to dump diesel and utilize cleaner-burning fuels. Five of six transit agencies in San Diego and 11 of 18 in the Los Angeles area moved to alternative-fuel buses. Progress has been much slower, and the source of much consternation for the board, in the Bay Area, however, where 13 of 15 transit agencies still use diesel buses.

Among Bay Area agencies, only Sonoma County Transit and Union City Transit embraced the non-diesel buses. The Bay Area bus fleet is 88 percent diesel, whereas Los Angeles is 50 percent.

Particularly frustrating for the board is that some agencies have failed to submit the required plans in reducing diesel emissions, which health officials claim is the worst source of air pollution. And now manufacturers say producing cleaner-burning diesel buses by the 2007 state requirement is not feasible, as research and development to satisfy stringent California rules are not cost effective while federal rules are more lax.