Michigan Highways: Since 1997.

Michigan Highways website header graphic
M-22 & M-109 junction route signage in Glen Arbor, Michigan

National Highway System in Michigan

The National Highway System (NHS) is, as the name implies, a nationwide system of primary highways and, although designated on a national basis, maintained by each of the states. Unlike the Interstates or US Highways, the NHS is not designated by a type of route designation or highway sign. Rather, the system was selected from existing highways by transportation officials in each state with assistance by county and local authorities. These officials were charged with selecting the streets, roads, highways and freeways with, according to MDOT, "the greatest state, regional and national significance."

The NHS was created as a part of the National Highway System Designation Act of 1995, signed into law on November 28, 1995 and expanded a few years later as a part of the Transportation Equity Act of the 21st Century (TEA-21), signed on June 9, 1998. For many years, the system stood at approximately 160,000 miles of Intestates, other freeways and various other principal highways. From MDOT, the stated objective of the National Highway System is to:

"Provide an interconnected system of principal arterial routes which will serve major population centers, international border crossings, ports, airports, public transportation facilities, and other intermodal transportation facilities and other major travel destinations; meet national defense requirements; and serve interstate and interregional travel."


MAP-21, the Moving Ahead for Progress in the 21st Century Act, was signed into law by President Obama on July 6, 2012 and contained many sweeping changes to Federal highway, bridge and transit programs and funding mechanisms. One of those changes was that MAP-21 expanded the National Highway System (NHS) to incorporate urban and rural principal arterials that were not included in the NHS before October 1, 2012. The "enhanced NHS" is a term used to refer to the National Highway System that was expanded or enhanced by MAP-21. (The term "enhanced NHS" is a general descriptive term and is not specifically cited as such in the statutory language.) The system was expanded from about 160,000 to about 230,000 total miles with these additions.

Investment at the Federal level targets the "enhanced NHS," with more than half of highway funding going to the new program devoted to preserving and improving the most important highways—the National Highway Performance Program. Under MAP-21, the enhanced NHS is composed of approximately 220,000 miles of rural and urban roads serving major population centers, international border crossings, intermodal transportation facilities, and major travel destinations. It includes the Interstate System, all principal arterials (only some of which had been designated as part of the NHS prior to 2012) and border crossings on those routes, highways that provide motor vehicle access between the NHS and major intermodal transportation facilities, and the network of highways important to U.S. strategic defense (STRAHNET) and its connectors to major military installations. Also effective October 1, 2012, there are no longer any restrictions on maximum number of miles of highway or street on the NHS.


As for mileage breakdowns, both the national and Michigan statistics from 2012 are presented below:

  Total Interstates Other State
County Roads
& City Streets
National 223,668 miles 47,328 miles 176,340 miles
Michigan 6,476 miles 1,244 miles 4020 miles 1,212 miles


Additional Information