The provisions of this title relating to vehicles shall be applicable and uniform throughout this state and in all incorporated cities and towns and all political subdivisions therein and no local authority shall enact or enforce any law, ordinance, rule or regulation in conflict with the provisions of this title except and unless expressly authorized by law to do so and any laws, ordinances, rules or regulations in conflict with the provisions of this title are hereby declared to be invalid and of no effect. Local authorities may, however, adopt additional vehicle and traffic regulations which are not in conflict with the provisions of this title.