It is hereby declared by the Legislature of Alabama that city and town streets and roads or portions thereof, including viaducts and bridges, which constitute the route of connection between or extension of state roads in the Alabama state highway system, hereby designated as municipal connecting link roads, have in the past, do now, and will in the future serve a state purpose and are for the general benefit of the state; and that it is a proper and legitimate function of the state to designate such municipal connecting link roads and to provide for the cost and manner and extent of maintenance, repair, construction, and reconstruction of the same by the state independently or in cooperation with the city or town involved.