42 U.S.C. § 7543 — State standards

(a) A State^* or political subdivision may not adopt or enforce a standard controlling emissions from new motor vehicles or engines covered by this part. A State also may not require certification, inspection, or other approval concerning emissions as a condition before initial retail sale, titling, or registration. (b)(1) After notice and a public-hearing opportunity, the Administrator^* must waive this section for a State that adopted non-crankcase emissions standards before March 30, 1966, if the State determines its standards are, overall, at least as protective of health and welfare as Federal standards. The Administrator may not grant a waiver if the State determination is arbitrary or capricious, the State does not need its standards for compelling and extraordinary conditions, or the standards and enforcement procedures conflict with section 7521(a). (2) A State standard at least as strict as the comparable Federal standard is deemed at least as protective. (3) For a vehicle or engine covered by a waiver, compliance with the State standard counts as compliance with the Federal standard. (c) When a regulation under section 7541(a)(2) covers a vehicle or engine part, no State or political subdivision may impose an emissions standard or certification, inspection, or approval requirement covering the same aspect of that part. This does not apply to a State with a waiver under (b). (d) This part does not take away a State or subdivision's otherwise existing power to control, regulate, or restrict the use, operation, or movement of registered or licensed vehicles. (e)(1) A State may not set or enforce emissions requirements for new nonroad engines or vehicles that are (A) construction or farm engines or vehicles under 175 horsepower or (B) new locomotives or locomotive engines. The waiver rule in (b) does not apply to this paragraph. (2)(A) For other nonroad vehicles or engines, after notice and a public-hearing opportunity, the Administrator must authorize California to adopt and enforce emissions standards if California determines its standards are overall at least as protective as Federal standards. Authorization must be denied if that determination is arbitrary or capricious, California does not need the standards for compelling and extraordinary conditions, or the standards and enforcement conflict with this section. (B) Another State with an approved part D, subchapter I plan may, after notifying the Administrator, adopt and enforce for any period identical standards and related actions if they are identical for that period to California standards authorized under (A), and California and that State adopt them at least 2 years before the period begins. The Administrator must issue regulations implementing this subsection.