§ 1181. Minimum speed regulations. (a) 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 or in compliance with law.

(b) Whenever a minimum speed limit has been established as authorized in sections sixteen hundred twenty or sixteen hundred forty-two, no person shall drive at a speed less than such minimum speed limit except when entering upon or preparing to exit from the highway upon which such a minimum speed limit has been established, when preparing to stop, or when necessary for safe operation or in compliance with law.