49 CFR § 355.25 - Adopting and enforcing compatible laws and regulations.
(a) General. No State shall have in effect or enforce any State law or regulation pertaining to commercial motor vehicle safety in interstate commerce which the Administrator finds to be incompatible with the provisions of the Federal Motor Carrier Safety Regulations.
(b) New state requirements. No State shall implement any changes to a law or regulation which makes that or any other law or regulation incompatible with a provision of the Federal Motor Carrier Safety Regulations.
(c) Enforcement. To enforce compliance with this section, the Administrator will initiate a rulemaking proceeding under part 389 of this subchapter to declare the incompatible State law or regulation pertaining to commercial motor vehicle safety unenforceable in interstate commerce.
(d) Waiver of determination. Any person (including any State) may petition for a waiver of a determination made under paragraph (c) of this section. Such petition will also be considered in a rulemaking proceeding under part 389. Waivers shall be granted only upon a satisfactory showing that continued enforcement of the incompatible State law or regulation is not contrary to the public interest and is consistent with the safe operation of commercial motor vehicles.
(e) Consolidation of proceedings. The Administrator may consolidate any action to enforce this section with other proceedings required under this section if the Administrator determines that such consolidation will not adversely affect any party to any such proceeding.