The Michigan Vehicle Code sets speed limits for roads even where no speed limit is posted. These unposted speed limits are known as "prima facie" speed limits. The prima facie speed limits identified in the law are:
Residential and Business Streets
Where no speed limit is posted, the prima facia speed limit on paved or gravel platted residential streets and streets in business districts is 25 mph.
Unless a different speed is posted, the prima facie speed limit in parks is also 25 mph.
On highways outside of residential or business districts, if no speed limit is posted, the prima facie speed limit is 55 mph.
Speed limits on gravel roads are not posted (unless in a platted subdivision) since conditions may vary widely from year to year. On gravel roads, if no speed limit is posted, the prima facie speed limit is 55 mph.