Other vehicles not herein defined by this chapter shall not be used for transportation of patients who must be carried on a stretcher or who may require medical attention en route, except that such transportation may be used when:
(1) A disaster creates a situation that cannot be served by licensed ambulances; or
(2) The use of a stretcher is necessary because an individual's personal mobility aid cannot be adequately secured in the nonambulance vehicle and the individual has written authorization from his or her physician that it is safe to transfer the individual from a personal mobility aid to a stretcher.