Section 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.