California Code, Health and Safety Code - HSC § 44250

(a) Existing programs to ensure that new motor vehicles sold in California emit less pollution may not be adequate to allow attainment of ambient air quality standards. Continued use of older high-emission motor vehicles, inadequate vehicle maintenance practices, and increases in vehicle miles traveled may overwhelm the gains from more stringent standards for new motor vehicles, and defeat state and local efforts to improve air quality.

(b) Substantial additional reductions in vehicle emissions can be achieved by retrofitting existing motor vehicles, enhancing vehicle maintenance practices, and installing additional pollution control equipment on new motor vehicles operated in nonattainment areas. Existing state programs are an impediment to the use of retrofits and additional equipment to reduce vehicle emissions and should be streamlined.

(c) Information on vehicle emissions should be provided to the driving public to encourage the manufacture and purchase of clean burning vehicles, to encourage retrofits of motor vehicles to reduce emissions, to encourage the application of enhanced motor vehicle maintenance practices on a routine basis, and to encourage reductions in vehicle miles traveled.