Section 31. The registrar may make rules and regulations governing the use and operation of motor vehicles or trailers and the conduct of operators and chauffeurs and may establish regulations to govern operators’ licenses, permits and identification cards and any other products the registrar is authorized to issue or which are provided by general or special law. A copy of the rules and regulations, attested by the registrar, shall be prima facie evidence that they have been adopted as provided by law. This section shall not be construed as giving the registrar power to regulate the speed at which motor vehicles may be operated on public ways.