Section 39-09-09 - Minimum speed limits1. An individual may not drive a motor vehicle at a reduced speed so 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. If the director and the superintendent of the highway patrol, acting jointly, or a local authority within the authority's jurisdiction, determines on the basis of an engineering and traffic investigation that slow speeds on any highway or part of a highway impede the safe, normal, and reasonable movement of traffic, the director and superintendent or the local authority may determine and declare a minimum speed limit below which an individual may not drive a vehicle except when necessary for safe operation or in compliance with law, and that limit is effective when posted upon appropriate fixed or variable signs.