1. A person shall not 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 or in compliance with law.
2. Whenever a public authority determines on the basis of an engineering and traffic investigation that slow speeds on any part of a highway consistently impede the normal and reasonable movement of traffic, such authority may establish a minimum speed limit below which no person shall drive a vehicle except when necessary for safe operation or in compliance with law.
3. Such speed limit shall be in effect after the erection of appropriate signs.