49 CFR 374.201: Prohibition against smoking on interstate passenger-carrying motor vehicles.

(a) All motor carriers of passengers subject to 49 U.S.C. subtitle IV, part B, shall prohibit smoking (including the carrying of lit cigars, cigarettes, and pipes) on vehicles transporting passengers in scheduled or special service in interstate commerce.

(b) Each carrier shall take such action as is necessary to ensure that smoking by passengers, drivers, and other employees is not permitted in violation of this section. This shall include making appropriate announcements to passengers, the posting of the international no-smoking symbol, and the posting of signs in all vehicles transporting passengers in letters in sharp color contrast to the background, and of such size, shape, and color as to be readily legible. Such signs and symbols shall be kept and maintained in such a manner as to remain legible and shall indicate that smoking is prohibited by Federal regulation.

(c) The provisions of paragraph (a) of this section shall not apply to charter operations as defined in § 374.503 of this part.