The term "street railroad" when used in this act includes every railway and each and every branch or extension thereof, by whatsoever power operated, being mainly upon, along, above or below any street, avenue, road, highway, bridge or public place within any city or county, or city or town, together with all real estate, fixtures and personal property of every kind and description used in connection therewith, owned, controlled, operated or managed for public use in the transportation of persons or property; but the term "street railroad" when used in this act shall not include a railway constituting or used as a part of a commercial or interurban railway.