California Code, Health and Safety Code - HSC § 39617

(a) The measurement of actual air emissions from those motor vehicles repaired or retired as a result of the rule, regulation, or control measure, pursuant to the methodology and criteria established pursuant to Section 39607.5, or, prior to adoption of the methodology by the state board, by any alternate methodology approved by the agency which has adopted the rule, regulation, or control measure, if that methodology is consistent with federal law and with subdivision (b) of Section 39607.5.

(b) The use of a statistically representative sample of the motor vehicles repaired or retired as a result of the rule, regulation, or control measure, utilizing the methodology and criteria established pursuant to Section 39607.5, or, prior to adoption of the methodology by the state board, by any alternate methodology approved by the agency which has adopted the rule, regulation, or control measure, if that methodology is consistent with federal law and with subdivision (b) of Section 39607.5.

(c) The use of vehicle fleet average emissions, as determined by the state board.

(d) This section does not apply to any motor vehicle specified in subdivision (a), (b), (f), or (k) of Section 34500 of the Vehicle Code.