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 Highway System covers about in the state and consists of four primary highways and nine auxiliary highways. There are additional 29 business routes associated with the system in Michigan. The longest segment of Interstate Highway in the state is Interstate 75 (I-75) at just under ; the shortest is I-375 at . The length of I-75, the longest highway of any kind in the state, includes the Mackinac Bridge, which is maintained by the MBA, the only section of state highway not under MDOT jurisdiction. The Mackinac Bridge is one of three monumental bridges in the state used by I-75; the others are the Zilwaukee and International bridges. A fourth, the privately owned Ambassador Bridge connects I-75 and I-96 in Detroit to Canada.