49 U.S.C. § 32511

(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—

(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 .