In 2000, the California Air Resources Board (CARB) adopted new standards that reduced emissions limits to 0.2 gram NOx for all new transit buses in the state beginning in 2007.
Now CARB, which is the only air quality regulating organization in the U.S. other than the EPA, is considering rolling back the standards to 1.2 grams NOx emissions or six times the pollution that the current rules would allow.
The current rules were enacted to help address California's worst-in-the-nation air pollution problems.
Since the rules were adopted, sound progress has been made in developing bus-engine technologies that pollute less.
Cummins Westport and John Deere Power Systems, for example, have already announced engines that will meet the 2007 standard.