(1) No motor vehicle shall be driven at a speed less than thirty miles per hour on federal designated highways where no hazard exists. An exception to this requirement shall be recognized when reduced speed is necessary for safe operation, or when a vehicle or combination of vehicles is necessarily, or in compliance with law or police direction, proceeding at a reduced speed. Police officers are hereby authorized to enforce this provision by directions to drivers. In the event of apparent wilful disobedience to this provision and refusal to comply with the direction of an officer in accordance herewith the continued slow operation by a driver shall be a misdemeanor.
(2) In the event a speed limit of seventy miles per hour is established on any portion of the Interstate Highway System or on four-laned U.S. designated highways as is provided in Section 63-3-501, a minimum speed of forty miles per hour shall be established for those vehicles having a maximum speed restriction of seventy miles per hour. Notice of said minimum speed shall be posted on such roads.