Michigan Highways: Michigan's Route Systems (2024)

The majority of the signed highway routes in Michigan belong to the state trunkline highway system: the 9,655-mile network of roads posted with Interstate-, US- or M-numbered route designations. Even though these three types of routes have different route markers, they are all part of the state trunkline highway system as designated by and the responsibility of the Michigan Department of Transportation (MDOT).

Beyond the state highway system, numbered-and-posted routes of various types exist. The three most prominent ones are the Intercounty Highway system, individually-designated county route systems, and the Forest Highways in the state's four National Forests. In addition, other highway designations exist which primarily overlay onto one of these numbered-highway systems, such as the Great Lakes Circle Tours, the Pure Michigan Byways (Heritage Routes), and other similar routes.

Michigan State Trunkline Record Holders – This PDF document details the record holders (as of December 2005) for both longest and shortest "regular" state trunkline routes, business connections and unsigned trunklines.

Interstate Highways
Of the entire 46,726.36-mile (47,908.07 route-mile) Interstate Highway System across the United States, 1,240.77 miles of that total (or 1,258.025 route-miles) are located in Michigan. Michigan has the place of being one of the first and last states to build portions of the original Interstate system! To compliment the Interstate Highway System, numerous Interstate Business Loops and Business Spurs help guide motorists from the Interstates and into or through the center of cities. Michigan's Interstates include:

US Highways
While the 157,724-mile US Highway system is also marked with standardized signs across the country, MDOT maintains the 2,528.6 miles of US Highways (including Business Connections) within the state of Michigan. Thirteen US Highways currently call Michigan home, but historically, that number has been as high as 18. As with the Interstates, numerous US Business Connections (Business Routes) are designated to provide marked loop or spur routes through or into cities. The US Highways in Michigan include:

State Highways
Somewhat of a misnomer as all Interstate-, US- and "M"-marked routes within Michigan are "State Highways," these routes bear the "M-nn" designation and route markers with the familiar diamond shape and block-letter "M" at the top. Michigan was the second jurisdiction in the world to both designate and post a numbered system of state trunkline highways in 1918–19. Wisconsin, Michigan's neighbor to the west, was the first place anywhere to have a numbered, signposted state highway system. After Wisconsin and Michigan marked their state highway systems, every other U.S. state and Canadian province eventually followed suit, as well as nearly every country around the world.

Intercounty Highways
A system of county-maintained routes begun in 1970 in an attempt to suppliment the state highway system. These routes are not a part of the state trunkline highway system, but are (somewhat) statewide in nature and loosely coordinated by MDOT. The system was begun to provide a consistent, statewide county numbering system for identifying primary county roads which retained their designations across county lines. More in-depth and historical information on these routes can be found on the Intercounty Highways page.

County-Numbered Roads
A more traditional system of county-numbered roads is currently in use by approximately 28 of Michigan's 83 counties, although some choose not to sign these routes in the field. In recent years, a few counties have shied away from the regular county road numbering system, relegating it to historical status on old road maps. These systems are not included within the scope of this website, although more information and/or links to additional information may be provided on them down the road. More information on these routes in general is found on the County Routes page.

Forest Highways
According to the Federal Government, "the Forest Highways Program provides funding to resurface, restore, rehabilitate, or reconstruct designated public roads that provide access to or are within a National Forest or Grassland. The program is administered by the Federal Highway Administration’s (FHWA) Federals Lands Highway Office, in partnership with the USDA Forest Service (FS) and 41 State Departments of Transportation, in accordance with tri-agency agreements in each state." There are approximately 20 designated Forest Highways in Michigan, although many of them are unsigned. See the Forest Highways page for more details.

Additional types of "other" highways in Michigan are detailed in the Other Highways section of this website.

Route Mileage by Signed System

The table at right displays route mileage by signed system (currently only state trunkline highways are included in this table). "Route mileage" will always be higher than system mileage, as the hundreds of miles of concurrent route designations will count for both systems, e.g. the 75 mile concurrent stretch of I-75/US-23 will count 75 miles toward the Interstate total and the US Highway total. Thus, the route mileage in this table should not be totaled, as it will add up to more than the actual state trunkline system (and give you a rather meaningless "total.") "Signed system" indicates the type of system, such as Interstate, US and State ("M"), although all of these are state trunkline highways under the jurisdiction of MDOT. (Data tabulated January 2022.)