The control of signs in areas adjacent to state highways of this state is hereby declared to be necessary to promote the public health, safety, welfare, convenience and enjoyment of public travel, to protect the public investment in the interstate system and other state highways, and to attract visitors to this state by conserving the natural beauty of areas adjacent to the interstate system, and of scenic areas adjacent to state highways upon which they travel in great numbers, and to insure that information in the specific interest of the traveling public is presented safely and effectively.