§ 1684. State highways maintained by the state. No local authority
shall place or maintain any traffic-control device on any state highway
maintained by the state, or at any location so as to prohibit, restrict
or limit the movement of traffic proceeding along, entering or crossing
such highway, nor shall any ordinance, rule or regulation affecting
traffic or stopping, standing or parking on state highways maintained by
the state be effective unless or until approval in writing has been
obtained from the department of transportation, and the department of
transportation may at any time rescind or modify such approval.