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 adopt traffic regulations which are not in conflict with the provisions of this chapter; provided, that when any local ordinance regulating traffic covers the same subject for which a penalty is provided for in this chapter, then the penalty provided for violation of said local ordinance shall be identical with the penalty provided for in this chapter for the same offense.