The department is authorized to maintain the rights-of-way, pavement, and structures of streets over which interstate highway traffic is routed within municipalities and designated by the commissioner as part of the interstate and defense system of highways as defined by the Federal Highway Act of 1956; provided, that the department shall have no authority to maintain or operate lighting systems for or on the streets, but cities and municipalities may maintain and operate the systems in accordance with standards prescribed by the commissioner; and provided, further, that they shall be maintained and operated at the expense of the cities and municipalities.