The Department of Transportation and local authorities shall erect and maintain at appropriate locations official signs on freeways under their respective jurisdictions apprising motorists of the restrictions placed upon the use of such highways by the Nebraska Rules of the Road. When the department or local authority posts such signs, it need not follow the usual rules and procedure of posting signs on or near freeways nor shall the department be required to conform with the formalities of public hearings. When such signs are erected, no person shall violate the restrictions stated on such signs.