Michigan's State Trunkline System

Most of the state trunklines comprising the 9,720.8-mile system are posted with either Interstate-, US- or M-numbered designations. Even though each of these different types of route designations have different route markers, they are marked and maintained by the Michigan Department of Transportation. Each of these three types of state trunklines are defined below. Following that is a table illustrating Route Mileage by Signed System.

Michigan State Trunkline Record Holders - This PDF document details the record holders for both longest and shortest "regular" state trunkline routes, business connections and unsigned trunklines.

Interstate Highways
Of the entire 46,567-mile Interstate highway system across the United States, 1,241 miles of that total are located in Michigan. Michigan has the place of being one of the first and last states to build portions of the Interstate system! To compliment the Interstate highway system, numerous Interstate Business Loops and Business Spurs help guide motorists from the Interstate highway and into or through the center of cities. Michigan's Interstate highways include:

US Highways
While the US Highway system is also marked with standardized signs across the country, MDOT maintains the approximately 2,400 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 sign 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 state and Canadian province eventually followed suit, as well as most countries around the world.

Other Highways

County-Designated (Intercounty) Highways
A system of county-maintained routes begun in 1970 in an attempt to suppliment the state highway system. While these routes are not a part of the Michigan state highway system, they are (somewhat) statewide in nature and are included for informational purposes. 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 County 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.

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. "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, although all of these are state trunkline highways maintained by MDOT. (Data tabulated August 2006.)