The State Trunkline Highway System is made up of all the highways designated as Interstates, U.S. Highways and State Highways in the US state of Michigan. The system is maintained by the Michigan Department of Transportation (MDOT) and comprises of trunklines in all 83 counties of Michigan on both the Upper and Lower peninsulas (UP, LP), linked by the Mackinac Bridge. The system ranges in size from the unsigned Business Spur Interstate 375 (BS I-375) at and signed M-212 at to Interstate 75 (I-75) at . Some trunklines in Michigan are maintained by MDOT but bear no signage along the route to indicate this. These unsigned trunklines are mostly segments of former highway designations that have been moved or had the designations . These segments remain under state control until the appropriate city or county accepts jurisdiction of the roadway from the state.