![Welcome sign along M-99](http://upload.wikimedia.org/wikipedia/commons/thumb/7/74/M-99_welcome_sign_cropped.jpg/150px-M-99_welcome_sign_cropped.jpg)
The State Trunkline Highway System consists of all the state highways in Michigan, including those designated as Interstate, United States, or State Trunkline highways. Maintained by the Michigan Department of Transportation, the system comprises 9,716 miles (15,636 km) of trunklines in all 83 counties of the state. Its components range in scale from 10-lane urban freeways to two-lane rural undivided highways to a non-motorized highway on Mackinac Island, where cars are forbidden. The longest highway is nearly 400 miles (640 km) long, while the shortest is about three-quarters of a mile (about 1.2 km). On May 13, 1913, the State Reward Trunk Line Highways Act was passed, creating the system. Highway numbers were first posted on signs in 1919, making Michigan the second state to do so. Michigan's first freeways were built during the 1940s. Construction on Michigan's Interstates started in the late 1950s and continued until 1992. Few additional freeways have been built since 1992, and in the early years of the 21st century, projects are underway to bypass cities with new highways.
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