Introduction

The 9,649-mile state trunkline system in Michigan is laid-out, designed, and marked by the Michigan Department of Transportation (MDOT), which is also responsibile for the system's maintenance, either directly or through contracting with local units of government. Michigan is regarded as being the second state in the U.S. to set up a numbered and posted state trunkline system. While Wisconsin is given the credit for creating the first such system in 1917, Michigan's was organized within a year after that. Even before that point, however, in 1913 the Michigan State Legislature passed the "State Trunk Line Act," which authorized the designation of a state highway network totalling almost 3,000 miles of roadway. The act stipulated the State Highway Department would design, build and maintain highway bridges 30 feet in length or longer, if the county or local government improved three miles of adjacent road.

As of 2021, there are 122,040 miles of roads in Michigan, with responsibility for these roads divided by the state (9,649 miles), counties (90,281miles), cities and villages (21,396 miles), and some in the federal jurisdiction (714 miles). According to MDOT, in 2010, Michigan ranked 48th in the U.S. in percentage of roads under the jurisdiction of the state as compared to all roads system in the state (7.9%). Also, 84% of Michigan's population currently resides within two miles of a road on the state highway system.

As for the highway route designations itself, Michigan generally does not have any special "practices," such as clustering of route numbers, with the exception of what could be termed a "minimalist" strategy. This is shown when a freeway or expressway is opened along a new alignment and the former route is generally turned back to local control. However, the mileage of the state trunkline system has, itself, remained relatively constant over the last several decades, with only 500 miles separating the minimum and maximum during that time peroid. The table below illustrates this:

	Total Mileage
Year	State Trunklines	County Roads	Municipal Streets	Total*
1960	9,308	86,145	15,203	110,656
1970	9,221	87,723	17,847	114,791
1980	9,502	88,799	19,070	117,371
1985	9,498	88,514	19,540	117,552
1989	9,527	88,634	19,820	117,981
1990	9,538	88,705	19,877	118,120
1991	9,615	88,770	19,945	118,330
1992	9,629	88,755	20,007	118,391
1993	9,607	88,742	20,118	118,467
1994	9,591	88,836	20,155	118,582
1995	9,602	88,890	20,239	118,731
1996	9,583	89,129	20,401	119,113
1997	9,630.0	89,128.2	20,402.0	119,160.2
1998	9,725.3	89,173.8	20,500.1	119,399.2
1999	9,725.3	89,344.1	20,569.9	119,639.3
2000	9,711.4	89,498.8	20,666.9	119,877.1
2001	9,714.1	89,606.2	20,737.0	120,057.3
2002	9,711.0	89,757.0	20,784.2	120,252.2
2003	9,721.7	89,876.6	20,841.4	120,439.7
2004	9,720.8	89,898.9	20,971.1	120,590.8
2005	9,695	88,961	20,914	119,570
2009	9,695	90,162	20,914	120,771
2010	9,655	90,208	21,247	121,110
2017**	9,669 14	89,444 764**	21,198 49**	120,256 854**
2021	9,649 20	90,281 837	21,396 198	122,040 1784
**Assumedly, a new method of calculating roadway mileage was implemented sometime between 2000 and 2017, which would account for the drastic decrease in the amout of roadway mileage, especially on the county road network.
Source: MDOT, Bureau of Transportation Planning, Asset Management Division, (517) 335-2608 *Totals do not include federally-owned mileage, such as forest roads and roads in federal installations.

MDOT does correctly note that "the density of development varies considerably throughout Michigan, with the heaviest concentration existing in the southeast portion of the lower peninsula." Even with this obvious disparity in settlement density, there has always been a level of "geographic equity" in the organization of the state highway system. MDOT notes their aim has been to "provide everyone with reasonable access to a state highway, regardless of where they live." Over the nearly 100-year history of the signed state highway system, MDOT and its predecessors have done a excellent job of adhearhing to their goal. With the changes coming to Michigan's state highway system, the Department of Transportation is committed to maintaining this balance. However, they state "the definition of 'reasonable access' may change, more or less proportionately, for everyone in Michigan."

Additional Information

For more in-depth information about the Michigan state trunkline system, please feel free to explore the many pages on this site using the drop-down menus at the top of each page or select from any of the items below:

• Michigan's Route Systems - information about the various types of signed highway route systems.
• Michigan's Route Markers - all about the diamond state trunkline marker in use since 1918, as well as the many other types of route markers used on and off the trunkline system ever since.
• Master List: 1913-Present - the comprehensive listing of every route designation ever used in Michigan.
• Highway Listings - every highway is listed here with facts. details and history about each.
• Historical Overview - historical highlights about the Michigan state trunkline system.
• The History of Roads in Michigan - a special section relating the history of roads from prehistoric Indian Trails to modern times.
• In Depth: News & Articles - in-depth stories, histories and information.