Iowa Code § 321.235 : TRANSPORTATION — VEHICLES — Motor vehicles and law of the road —OBEDIENCE TO AND EFFECT OF TRAFFIC LAWS — Provisions uniform

The provisions of this chapter shall be applicable and uniform throughout this state and in all political subdivisions and municipalities therein and no local authority shall enact or enforce any rule or regulation in conflict with the provisions of this chapter unless expressly authorized herein. Local authorities may, however, adopt additional traffic regulations which are not in conflict with the provisions of this chapter.