Whenever, in order to serve the public convenience, any street railway or traction company is lawfully operating autobusses in conjunction with its street railway lines, and its autobusses and street railway lines are operated by such company as a co-ordinated system of street transportation, such company as to such system shall be deemed in all respects and for all purposes to be a single public utility furnishing a single service subject to the supervision and regulation, jurisdiction and control of the board of public utility commissioners; provided, that nothing in this section shall in any way change the method of taxation of companies operating street railways and autobusses now provided by law nor in any way change the terms or duration of any franchise or consent to operate or the necessity for municipal consent.