In order to promote public safety, health, welfare, convenience and enjoyment of public travel, to protect the public investment in public highways and to preserve and enhance the scenic beauty of lands bordering public highways, it is the public policy of this state to regulate the erection and maintenance of outdoor advertising and the establishment, operation and maintenance of junkyards in areas adjacent to the interstate and primary systems in accordance with the Highway Beautification Act. The legislature finds that regulation of outdoor advertising and junkyards is for a highway purpose.