What is the difference between California and federal vehicles? Why do automakers make cleaner and dirtier versions of the same model?
California has more health protective vehicle emissions standards than the US government. Thus, a typical vehicle sold in California is cleaner than its federal counterpart. Because our 1985-2000 Auto Asthma Index values were developed using data from California-certified vehicles only, they represent a best-case scenario in terms of smog chemical pollution. For newer cars the Auto Asthma Index takes into account where you live, as well as available emissions data. If you select California, New York, Maine or Vermont–all states that require that vehicles sold within their borders meet California’s emissions standards–your vehicle Auto Asthma Index will be based on the cleanest vehicle sold. However, if only Federal models were tested, your Index is based on these records and may be elevated. In addition to difference between cars sold in “clean” states, automakers often produce different versions of the same model vehicle, which are certified to meet different emissions standards. Wh
