List of Interstate Highways
There are 70 primary Interstate Highways in the Interstate Highway System, a network of controlled-access freeways in the United States. They are assigned one- or two-digit route numbers, whereas their associated "auxiliary" Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south-north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west-east, with lower numbers in the south and higher numbers in the north. Highways whose route numbers are divisible by "5" usually represent major coast-to-coast or border-to-border routes (ex. I-10 travels from Santa Monica, California, to Jacksonville, Florida, traveling from the Pacific to Atlantic oceans). Additionally, auxiliary highways have their numbering system where a different number prefixes the number of its parent highway.
List of Interstate Highways in Michigan
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 . The longest of these, Interstate 75 (I-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 (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO), while the highways in Michigan are maintained by the Michigan Department of Transportation (MDOT) and the Mackinac Bridge Authority (MBA). 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.