The
State Trunkline Highway System consists of all the
state highways in
Michigan, including those designated as
Interstate,
United States Numbered (US Highways), or State Trunkline highways. In their abbreviated format, these classifications are applied to highway numbers with an
I-,
US, or
M- prefix, respectively. The system is maintained by the
Michigan Department of Transportation (MDOT) and comprises of trunklines in all
83 counties of the state on both the
Upper and
Lower peninsulas (UP, LP), which are linked by the
Mackinac Bridge. Components of the system range in scale from 10-lane urban
freeways with
local-express lanes to two-lane rural
undivided highways to a non-motorized highway on
Mackinac Island where cars are forbidden. The longest highway is nearly long, while the shortest is about three-quarters of a mile (about 1.2 km). Some roads are
unsigned highways, lacking signage to indicate their maintenance by MDOT; these may be remnants of highways that are still under state control whose designations were
decommissioned or roadway segments left over from realignment projects.