Mich. Comp. Laws § 247.655
All roads, streets and highways included in the county primary road system of any county shall be officially known as county primary roads, and all roads, streets and highways included in the county local road system of any county shall be officially known as county local roads. For a period of 2 years after the effective date of this act, the primary road system and the local road system in each county, and the mileage in each such system used for all purposes under the provisions of this act, shall be as determined by the state highway commissioner, and thereafter the local road system and the primary road system in each county, and the mileage in each such system used for all purposes under the provisions of this act, shall be as established by certification to and approved by the state highway commissioner pursuant to the provisions of this act.
MCL 247.655