(a)(1) No person shall drive a motor vehicle at such a slow speed as to impede the normal and reasonable movement of traffic, except when reduced speed is necessary for safe operation.

(2) On roads, streets, or highways with two or more lanes allowing for movement in the same direction, no person shall continue to operate a motor vehicle in the most left-hand lane at less than the maximum lawful speed limit once such person knows or should reasonably know that he is being overtaken in such lane from the rear by a motor vehicle traveling at a higher rate of speed, except when such motor vehicle is preparing for a left turn.

(b) Whenever the commissioner of public safety or the commissioner of transportation or local authorities determine on the basis of any engineering and traffic investigation that slow speeds on any part of a road under their respective jurisdictions impede the normal and reasonable movement of traffic, such commissioners jointly, or such local authorities, may determine and declare a minimum speed limit below which no person shall drive a vehicle except when necessary for safe operation, and that limit shall be effective when posted upon fixed or variable signs.