The State Trunkline Highway System of the US state of Michigan is a network of roads owned and maintained by the Michigan Department of Transportation (MDOT). The most prominent of these roads are part of one of three numbered highway systems in Michigan: Interstates Highways, US Highways, and the other State Trunklines. Other systems of roads are operated by the 83 counties in the state as well as each city.
Interstate Highways and US Highways are assigned at the national level. Interstate Highways are numbered in a grid—even-numbered highways are east–west highways (but the lowest numbers are along Mexico and the Gulf of Mexico), and odd-numbered highways are north–south highways (with the lowest numbers along the Pacific Ocean). US Highways are also numbered in a grid—even numbered for east–west highways (with the lowest numbers along Canada) and odd numbered for north–south highways (with the lowest numbers along the Atlantic Ocean). For this reason, mainline (two-digit) Interstate Highways in Michigan all have numbers above 69 and mainline US Highways all have numbers below 45. Three-digit Interstate and U.S. Highways, also known as "child routes," are branches off their main one- or two-digit "parents". The Interstate and US Highways are maintained by MDOT. Interstate 75 (I-75) and US Highway 23 (US 23) are the longest examples in the state.
State Trunklines are the other state highways maintained by MDOT. These highways are completely owned and maintained by the state. Michigan highways are properly referred to using the M and never as "Route 28" or "Highway 115", but as M-28 or M-115. The marker used for state trunklines is a diamond with a block-letter "M" at the top. Roads that are maintained by the state but not assigned a state trunkline designation carry an unsigned highway designation.
County-Designated Highways are assigned numbers in a zone system by MDOT, but maintained by the counties. Each zone is indicated by a letter A–H which is followed by a number based on a grid inside that zone. Each county also maintains any other roadway that is not a state trunkline or a city street. The numbering and signing practices vary from county to county, as does the size of each county's system. Numerical designations typically do not carry over from one county to the next; a CDH that crosses county lines keeps its designation in each county however. County road designations are typically abbreviated "CR" or "Co Rd" followed by the number, and CDHs are abbreviated to just their letter and number assignment.
I-94 enters the state south of New Buffalo and runs eastward through several metropolitan areas in the southern section of the state. The highway serves Benton Harbor–St. Joseph near Lake Michigan before turning inland toward Kalamazoo and Battle Creek on the west side of the peninsula. Heading farther east, I-94 passes through rural areas in the middle of the southern Lower Peninsula and runs through Jackson, Ann Arbor, and portions of Metro Detroit, connecting Michigan's largest city to its main airport. Past the east side of Detroit, I-94 angles northeasterly through farmlands in The Thumb to Port Huron, where the designation terminates on the Blue Water Bridge at the Canadian border. The first segment of what later became I-94 within the state, the Willow Run Expressway, was built near Ypsilanti and Belleville in 1941, with an easterly extension to Detroit in 1945. By 1960, the length of I-94 was completed from Detroit to New Buffalo. Subsequent extensions in the 1960s completed most of the rest of the route, including the remaining sections between Detroit and Port Huron which superseded the routing of US 25. The last segment opened to the public in 1972 when Indiana completed its connection across the state line. Since completion, I-94 has remained relatively unchanged; a few interchanges have been rebuilt, a second span was constructed for the Blue Water Bridge, and in 1987, a plane crashed on the freeway during take off from the airport in Detroit. (more...)
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