Michigan/highway classification

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This is a proposal for standardized road classifications in Michigan as part of a larger discussion about classification standards nationwide (United States/Highway classification). You're free to add on and edit the contents of this page.


There has been no thorough effort to determine which highways in Michigan should be classified "trunk", "primary", etc. The following has been located on Michigan for much of the recent past:

However, this does not provide details on which particular routes should be tagged with certain classifications. Recent country-wide discussions for the US have established that trunk classification should be used for:[1]

  • urban expressways that have restricted access (but are not fully limited-access, so are not freeways)
  • roads that serve as the main connection between regionally-important population centers

Additionally, "spurs" and isolated sections of trunk road should be avoided, except when due to geographical limitations.

Michigan-specific considerations

Michigan effectively has two separate road networks, in the Upper and Lower Peninsulas, with only a single road connection between them (the Mackinac Bridge, which as part of I-75 is tagged motorway). The "regional importance" of cities varies vastly across the state; Marquette has 20k people and is the largest and most important city in the Upper Peninsula, while a suburb of Detroit with 20k people is not nearly as important.

City "importance" classifications

Tier 0

The largest and most prominent cities across all of Michigan, these also are potentially worthy of considering having a different road classification system within their greater urban boundaries.

  • Detroit metro area
  • Grand Rapids metro area

Tier 1

All tier 1 cities should generally be connected by motorway and/or trunk roads.

Lower Peninsula
  • Lansing
  • Ann Arbor
  • Flint
  • Kalamazoo
  • Battle Creek
  • Saginaw
  • Midland
  • Muskegon
  • Holland
  • Bay City
  • Jackson
  • Port Huron
  • Traverse City
Upper Peninsula
  • Marquette
  • Sault Ste Marie
  • Houghton
  • St. Ignace
  • Escanaba
Out-of-state cities
  • Toledo, OH
  • Duluth, MN
  • South Bend, IN
  • Green Bay, WI

Tier 2

  • TBD

Trunk routes

Long-distance routes classified as trunk (Lower Peninsula)

Corridor Endpoints Reason
US-31 US-10 to I-75 Connection from Holland and Muskegon to Traverse City, and from Traverse City to Mackinac Bridge.
US-131 end of freeway segment to US-31 Connection from Grand Rapids to Traverse City (via M-113 and M-37) and Upper Peninsula.
M-113 and M-37 US-131 to US-31 Connection from Grand Rapids to Traverse City.
M-72 I-75 to US-31 Connection from southeastern MI to Traverse City.
M-46 I-75 to US-131 Connection from Saginaw and Bay City to Grand Rapids, Muskegon, etc.
M-20 US-10 and US-127 Connection from Midland to Grand Rapids, Muskegon, etc.
M-46 US-131 to BUS US-31 Connection from tri-cities to Muskegon.
M-96 and BL I-94 and M-89 and M-40 I-94 to US-31 Connection from Battle Creek to Grand Rapids and from Kalamazoo to Holland.
US-223 and US-127 US-23 to I-94 Connection from Toledo to Jackson and Lansing
US-127 St. John's and Ithaca Freeway gap
US-31 Holland to Grand Haven Freeway gap

Long-distance routes classified as trunk (Upper Peninsula)

Corridor Endpoints Reason Current status
M-28 I-75 to US-2 (entire length) Major east-west route across UP. Connects Sault Ste. Marie, Marquette, Ironwood. Trunk. Route should be checked for any mapping errors.
US-2 I-75 to Wisconsin border Major east-west route across southern UP. Between I-75 and M-77 especially important for connecting LP to Marquette; also connects Escanaba to points west. Trunk.
M-77 US-2 to M-28 Part of ideal route between LP and Marquette. Trunk.
M-35 US-41 (Menominee) to US-41 (Escanaba) Route between Marquette and Green Bay. Trunk.
US-41 Wisconsin border to M-35; M-35 to US-2 Route between Marquette and Green Bay. Trunk.
US-41 M-28 to M-26 Route between Marquette and Houghton. Trunk.
US-45 and M-26 M-28 to US-41 Route between Duluth and Houghton. Trunk.
US-141 Entire route. Trunk route between Houghton and Green Bay. Trunk.

Urban trunks


  • M-102 from I-94 to M-5 and M-5 until it becomes a freeway
    • currently mapped as a trunk route
  • US-24 from I-75 (near Taylor) to I-75 (north of Pontiac), and connector from I-75 to US-24 south of Pontiac
    • major route for traffic through suburbs, also serves as a thru route for traffic from southwest (Ann Arbor, Canton, etc) to Pontiac area
  • M-153 from US-24 to I-94
    • major route for traffic, built to mostly expressway standard with some free-flowing interchanges
    • partially tagged as a trunk route (currently trunk-tagged section doesn't start/end at other freeways/trunk routes)
    • problem: unclear exactly which parts of intersection with I-94 and US-12 to tag as trunk
    • problem: if we tag this as trunk, maybe a section of US-12 is also worthy of trunk status? would this be over-tagging?
  • Detroit-Windsor Tunnel, Ambassador Bridge, and Sault Ste. Marie International Bridge
    • major international connections. Detroit-Windor Tunnel and Ambassador Bridge could potentially be downgraded once the Gordie Howe International Bridge is finished. currently, both Windsor border crossings should be trunk (tunnel is better for cars than the bridge, but hgv can only use bridge)