All authority, power, and duties conferred by law upon the commission as to steam railways, express and telegraph lines in this State, steamboat lines, and truck lines doing business as common carriers within this State are extended and conferred upon the commission as to all interurban railways, whether steam, electricity, or other power is used by them and whether or not the roads are partly without the corporate limits of towns or cities. The commission may not fix or approve the rates, fares, or charges for interurban railways.