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.