23 CFR § 1215.5 - Exemptions.
(a) Safety belt use laws exempting persons with medical excuses, persons in emergency vehicles, persons in the custody of police, persons in public and livery conveyances, persons in parade vehicles, persons in positions not equipped with safety belts, and postal, utility and other commercial drivers who make frequent stops in the course of their business shall be deemed to comply with 23 U.S.C. 153.
(b) Safety belt use laws exempting vehicles equipped with air bags shall be deemed not to comply with 23 U.S.C. 153.
(c) An exemption not identified in paragraph (a) of this section shall be deemed to comply with 23 U.S.C. 153 only if NHTSA and FHWA determine that it is consistent with the intent of § 1215.4(a), and applies to situations in which the risk to occupants is very low or in which there are exigent justifications.