1. Except under subsections 2 and 3, a street, road, or highway in the state highway system or any other township, county, or state road or highway may not be posted in a manner which reduces the maximum speed limit on the street, road, or highway by more than twenty miles [32.19 kilometers] per hour between two signs posted in a speed zone.

2. The maximum speed limit reductions between two fixed or variable signs in a variable speed limit adjustment zone may exceed twenty miles [32.19 kilometers] per hour when speed limits are lowered temporarily by the director due to unsafe conditions.

3. The maximum speed limit reduction between two signs posted in a highway construction zone may not exceed thirty miles [48.28 kilometers] per hour.