625 ILCS 5/11-207

Provisions of this Chapter uniform throughout State. 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 ordinance 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, but such regulations shall not be effective until signs giving reasonable notice thereof are posted.