page_title: List of Interstate Highways in Michigan
section_title: History
hierarchical_section_title: List of Interstate Highways in Michigan / History
caption_attribution_description: Michigan portion of Interstate Highway plan approved June 27, 1958
context_page_description: The Interstate Highways in Michigan are the segments of the national Dwight D. Eisenhower System of Interstate and Defense Highways that are owned and maintained by the U.S. state of Michigan, totaling about 1,239 miles. The longest of these, Interstate 75, is also the longest highway of any kind in the state. On a national level, the standards and numbering for the system are handled by the Federal Highway Administration and the American Association of State Highway and Transportation Officials, while the highways in Michigan are maintained by the Michigan Department of Transportation and the Mackinac Bridge Authority. The Interstates in Michigan have their origins in World War II-era expressways built in the Detroit area. After the system was created in 1956, the state highway department completed its first border-to-border Interstate in 1960. The last highway was completed in 1992, giving Michigan a total of 13 Interstate freeways. The original allotment of mileage to Michigan which would receive federal funding was expanded in 1968, and the United States Congress designated an additional highway in the 1990s that has not yet been built.
context_section_description: Construction of the first expressways in Michigan predates the Interstate Highway System. During World War II, the Michigan State Highway Department (MSHD) built the Willow Run and Detroit Industrial expressways (now part of I-94) to carry workers from Detroit to the defense plants at Willow Run Airport. The state created the Michigan Turnpike Authority (MTA) in 1951, which proposed the construction of a toll freeway to run north–south in the state. The original termini for the Michigan Turnpike were Bridgeport and Rockwood. Interagency politics stalled progress on any proposed turnpikes while MSHD had three freeways under planning or construction.
  The Interstate Highway System was authorized by the Federal Aid Highway Act of 1956, and the state had already designed several freeways for its portion of that system. Seizing the opportunity brought by a 1957 state law, the department sold $700 million in bonds (equivalent to $4.88 billion in 2011) in the late 1950s and early 1960s to finance land purchases and construction of the new freeways. The goal was to connect every city with a population over 50,000 with four-lane freeways that could accommodate rural traffic traveling at 70 mph (110 km/h). The MSHD delayed numbering these freeways as part of the Interstate Highway System until the federal government had finalized the designations to be assigned to Michigan's freeways. The first highway to be signed as an Interstate in Michigan was I-75, which received signage in late 1959, along a section near the Ohio state line that opened to traffic in October 1957. I-94 was the first of the Interstates to be completed border to border in a US state. In 1974, the state implemented mileage-based exit numbers along the Interstates in Michigan.
  The MSHD asked for 600 miles (970 km) in additions to the state's Interstate mileage in 1968. Included in these requests were the extension of the Davison Freeway (now M-8), the extension of I-69 from Marshall to Port Huron, and the conversion of the northern sections of US Highway 23 (US 23) and US 131. Of these, the I-69 proposal was approved when the United States Congress extended it to terminate in at I-75 in Flint. The highway was lengthened twice more: to I-475 in 1973 and to Port Huron on February 10, 1987. These last two extensions were classified non-chargeable mileage, or segments not financed through the Interstate Highway fund. The federal government paid 90 percent of the cost of the chargeable mileage originally approved.
  The last of Michigan's Interstates to be completed was I-69, the last segment of which opened in 1992. Since then, the United States Congress has designated an additional primary Interstate, I-73 in the state. All studies by MDOT on that highway were cancelled in 2001 over funding concerns. Press reports state there is a "lack of need" for the freeway in the state, and the department has no plans to revive I-73 as of 2011.
  If built as designated, I-73 would cross into Michigan near Toledo, Ohio, and connect Jackson, Lansing, and Clare to I-75 at Grayling.
caption: 1958 planning map for Michigan's Interstate Highways
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