49 U.S.C. § 32511: Relationship to other motor vehicle standards

(a) Preemption.—Except as provided in this section, a State or a political subdivision of a State may prescribe or enforce a bumper standard for a passenger motor vehicle or passenger motor vehicle equipment only if the standard is identical to a standard prescribed under section 32502 of this title. (b) Enforcement.—This chapter and chapter 301 of this title do not affect the authority of a State to enforce a bumper standard about an aspect of performance of a passenger motor vehicle or passenger motor vehicle equipment not covered by a standard prescribed under section 32502 of this title if the State bumper standard—(1) does not conflict with a standard prescribed under chapter 301 of this title; and (2) was in effect or prescribed by the State on October 20, 1972. (c) Additional and Higher Standards of Performance.—The United States Government, a State, or a political subdivision of a State may prescribe a bumper standard for a passenger motor vehicle or passenger motor vehicle equipment obtained for its own use that imposes additional or higher standards of performance than a standard prescribed under section 32502 of this title.