D.C. Mun. Regs. tit. 29, § 509
509.1 The following shall be exempt from the provisions of §§500 through 508 of this chapter:
(a) The unexpected use of a privately owned vehicle, not ordinarily used in the business of transporting persons who are sick, injured, wounded, or otherwise incapacitated or helpless in the performance of a lifesaving act;
(b) A vehicle rendering services as an ambulance in the case of a major catastrophe, disaster, or in an emergency when licensed ambulances are or may be insufficient to render the services required, and the Mayor has requested that the vehicle be so used;
(c) A vehicle, such as a Red Cross vehicle, stationed and available at a public event where an emergency is not anticipated by the organizer of the event or by District officials, which vehicle may be used to transport persons away from the event, provided an emergency, as defined in §599, does not exist;
(d) Ambulances owned and operated by the United States government;
(e) Ambulances based outside the District which do not constitute public vehicles for hire; and
(f) Vehicles operated solely for the transportation of non-ambulatory and handicapped patients to and from treatment facilities as out-patients; Provided, that this exemption shall not apply to any vehicle which is in any way held out as an ambulance.
509.2 For the purposes of this section, the following acts shall be deemed to be conclusive proof that a vehicle is held out as an ambulance:
(a) The use of the word "ambulance" on the vehicle, or in any advertising for the vehicle or the company that operates it, or in the company name;
(b) The marking of a vehicle, as with dome lights, sirens, or the like, in a fashion reasonably likely to create the impression that the vehicle is available for emergency transportation;
(c) The advertising of the vehicle or the company which owns it in the "Ambulance" section of the "Yellow Pages," or in any place where ambulance or emergency services are advertised;
(d) Any advertising of the vehicle or the company which is designed to inform the public of the availability of the transportation service for non-ambulatory or handicapped patients which does not state in clear, express terms that the vehicle is not equipped to supply emergency service as an ambulance; and
(e) Other acts that the Mayor may designate.
509.3 The Mayor shall establish rules to ensure that ambulances and ambulance personnel based outside of the District, but receiving patients within the District for transport to a location within the District, shall meet the substantive standards of §§502 through 504 of this chapter.
SOURCE: Rules of the Board of Public Welfare issued July 28, 1950; as amended on September 29, 1950.