Okla. Stat. tit. 66, § 66-204: Operation of buses

Owners of franchises for the operation of electric street

railways propelled by means of tracks and trolleys shall have full

power and authority under such franchises to extend such

transportation system by means of buses or other self-propelled

vehicles, and such transportation shall be and become a part of the

general transportation system of such street railway company,

subject to all regulations imposed on such vehicles by law.