Established in 1967 to define air quality standards for California's unique topography, CARB set forth guidelines for low-emission and zero-emission cars in 1990 that have since been adopted by NY State and served as the back-bone of the strict Federal EPA "Tier 2" auto emissions regulations. Observers now expect that the pollution reduction course California has laid for its 8,500 transit buses will similarly lead to nation-wide standards and regulatory action.

CARB's board - made up of 11 industry, public health and government members - also see wider implications. CARB Executive Officer Michael Kenny told the Sacramento Bee he believes bus emissions innovations will smooth the way for future rules regarding school bus, garbage truck and eventually commercial truck and construction equipment emissions.

The CARB regulations set clear and ambitious goals for reducing particulate and NOx emissions with incremental deadlines while offering two paths for transit fleets to reach them. The "alternative fuel" path requires 85% of all new buses to burn compressed or liquefied natural gas, propane or methanol. The "diesel" path allows fleets to buy diesel buses, but beginning in July 2002, all buses must use low sulfur diesel fuel and be fitted with particulate-catching filters and other control devices (the rule may drive commercial availability of some of this technology, which is mainly experimental now). The emission standard may be so tight that agencies will have to retire the oldest, most polluting buses. By the turn of 2004 both particulate and NOx emissions from diesels must be down by 80% and 75% respectively. "Diesel" path agencies must participate in early tests of zero-emission fuel cell buses, and attain a 15% share of zero-emission bus purchases two years ahead of "alternative fuel" agencies (2008).

In both cases, all diesel buses must be retro-fitted with pollution control technology by 2002, the first time in the history of the nation's air pollution regulation that a new requirement will apply to vehicles already on the road. All agencies with fleets larger than 200 must have fuel cell or electric zero-emissions buses as 15% of all new purchases by 2010.

CA transit agencies called the reduction goals fair, but had a variety of views about which path to take. Sacramento officials said they favored CNG buses due to their lower operating costs.