Vehicle manufacturers in the US fear an appeals court ruling on Southern California regulations could lead to other cities and states there demanding costly alternative fuel technologies.

In a decision that could set a precedent for local governments across the United States, the US Ninth Circuit Court of Appeals ruled that rubbish haulers, school and city bus lines and other publicly funded fleets in Southern California can be required to buy low-polluting vehicles run on natural gas or other alternative fuels, according to the Los Angeles Times (LAT).

The state of California is usually the US leader on environmental issues. Its largest city, Los Angeles, is especially prone to smog, and it was first to impose stringent pollution controls on vehicles several decades ago. Its current emissions rules, nowadays shared with several east coast states, are more stringent than the federal regulations. Southern California cities, in particular also have strict rules governing new building energy use and waste recycling.

The Los Angeles Times said private and federal [government] fleets such as Federal Express and the US Postal Service might not be covered under such rules requiring low-pollution vehicles, because the federal Clean Air Act might trump local regulation, and added that the appeals court had sent that portion of the case back to district court to decide separately.

Last April, the state of California won a major victory in its campaign to regulate greenhouse gases at the US Supreme Court, prompting a vigorous response from automakers' and environmental groups and the deferal Environment Protection Agency (EPA).

Southern California air regulators and environmental groups expressed satisfaction with Monday's appeal court ruling, the LAT reported on its website.

"We're thrilled," Barbara Baird, principal deputy counsel for the South Coast Air Quality Management District, was quoted as saying on Tuesday (21 August). "We really need the emissions reductions from these rules, and this case may set an important precedent for other state and local governments that want to adopt clean fleet provisions."

"The natural gas buses and garbage trucks on the streets every day aren't there by chance. They exist because of our victories in this litigation," David Pettit, a senior lawyer with the Natural Resources Defence Council and director of its Southern California Air Programme, told the Los Angeles Times. The paper noted that an estimated 6,000 new vehicles, mostly powered by compressed natural gas, have been purchased by agencies in the region since the rules were put in place.

It also cited regulators as saying that old school buses and other diesel vehicles are among the dirtiest on area roads, contributing to both diesel soot [ie particle emissions] and smog and that purchasing new, alternative-technology vehicles might initially be more costly than buying diesel equipment, but saves lives and costs in the long run.

According to the LAT, petroleum and engine manufacturing groups said the battle wasn't over, and noted that diesel technologies are becoming equally clean.

"Clearly we're disappointed that the Ninth Circuit ruled this fleet rule does apply to purchases by state and local government, but the appeals court . . . remanded it back to district court to decide whether or not this can apply to private fleets," Tupper Hull, spokesman for the Western States Petroleum Association, told the paper.

Joe Suchecki, spokesman for the Engine Manufacturers Association, whose organisation, the LAT said, has vigorously fought Southern California's regulations because they could spread to other states and cities, creating a "patchwork of different regulations" that would make it difficult and costly to manufacture different equipment for different localities, said: "They do get to continue to enforce rules on local governments."

According to the report, Suchecki and Jed Mandel, president of the engine manufacturers group, said AQMD's rules are out of date because they ban diesel engines and fuels, both of which have made huge strides toward cleaner technology in recent years due to US federal and state laws.

But AQMD spokesman Sam Atwood reportedly countered that claim by saying natural gas engines are years ahead of diesel technologies on meeting federal and local standards - he added that the district's regulations had put pressure on diesel manufacturers to clean up their act or lose a lot of business.

"If and when diesel engines are as clean as natural gas," then agencies will no longer be banned from purchasing them, he was quoted as saying.