The Michigan Vehicle Code sets speed limits for roads even where no speed limit sign 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 a residential subdivision street (as defined by Section 257.627) or street in a business district (as defined by Section 257.627) is 25 mph.
Parks
Unless a different speed is posted (no lower than 15 mph) the prima facie speed limit in parks is also 25 mph.
county roads
On county roads, outside of cities or villages, if no speed limit is posted, the prima facie speed limit is 55 mph.
Gravel Roads
Speed limits on gravel roads are not posted (unless in a residential 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.