Cal. Health and Safety Code § 39667

Based on its determinations pursuant to Section 39662, the state board shall consider the adoption of revisions in the emission standards for vehicular sources and regulations specifying the content of motor vehicle fuel, to achieve the maximum possible reduction in public exposure to toxic air contaminants. Except for regulations affecting new motor vehicles which shall be based upon the most advanced technology feasible for the model year, regulations developed pursuant to this section shall be based on the utilization of the best available control technologies or more effective control methods, unless the state board determines, based on an assessment of risk, that an alternative level of emission reduction is adequate or necessary to prevent an endangerment of public health. Those regulations may include, but are not limited to, the modification, removal, or substitution of vehicle fuel, vehicle fuel components, or fuel additives, or the required installation of vehicular control measures on new motor vehicles.