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:
See United States Highway Classification for the most up to date information on this topic.
The primary language and terms of OSM is UK English, which can be confusing. Use the table below to properly categorize streets in the area. Some effort has been made to cross-reference the National Functional Classification (NFC) numbers found using the State of Michigan NFC Map to the equivalent OpenStreetMap highway type. Please edit any errors, or start a discussion accordingly.
|State's NFC name (#)||OSM Type||Description|
|Interstate (1), Other freeways (2)||highway=motorway||Limited access freeway with interchanges. Access via on/off ramps with merge lanes, divided road of at least 2 lanes each direction. Called "Freeway." Speed limits generally 55 MPH or higher. Examples; 127, I96, I69, 496|
|Other Principal Arterials (3)||highway=trunk||
Rural: Nearly a freeway. Example, 127 North of St Johns.
Urban: May have cross traffic, but traffic flow on the trunk always has the right of way (except at red traffic lights). Speed limits usually 45 MPH or higher. Example, Saginaw Highway east of East Lansing.
Note, this is unrelated to our similarly named "State Trunkline" which the State of Michigan defines as, "all roads under MDOT jurisdiction, including all Interstate routes, US routes, M routes, Interstate business loops and spurs, US business routes, M business routes, connector routes, and unsigned state trunkline in Michigan."
|Minor Arterials (4)||highway=primary||
Rural: When tempted to tag a rural road as "trunk", it is probably an OpenStreetMap "primary" highway. Examples; M 52, M 99, M 100, M 115.
Urban: Three lanes or more each traffic direction. 35 MPH or faster. Handles large volumes of traffic. (Any or all of these). Examples Saginaw and Oakland through Lansing.
|Major Collectors (5)||highway=secondary||
Rural: The next class of roadway off a primary.
Urban: Two lanes of traffic each direction. 35 MPH or faster. Medium-high traffic volumes. Examples; Cedar Street and MLK in Lansing.
|Minor Collectors (6)||highway=tertiary||
Rural: If not sure, consider "unclassified", "residential", or "service".
Urban: Lower traffic volumes on wide streets, or higher traffic volumes on narrow ones. Examples; Mt. Hope, Jolly, Okemos, Willow, Creyts, Meridian
|Local (7)||highway=unclassified||The least most important through roads in a country's system – i.e. minor roads of a lower classification than tertiary, but which serve a purpose other than access to properties. For instance, minor country roads, often linking villages and hamlets. (The word 'unclassified' is a historical artifact of the UK road system and does not mean that the classification is unknown; you can use highway=road for that). Examples; Washington, College, Farm Lane, Freiermuth, Dobie.|
|Local (7)||highway=residential||Roads which serve as an access to housing, without function of connecting settlements. Often lined with housing. Single traffic lane each direction, may also be oneway=yes. Usually 25 MPH or slower. May have traffic bumps and other "traffic calming" measures. Examplesl apartment complexes, neighborhood roads|
to define a service way in more detail add service=*
|For access roads to, or within an industrial park, camp site, business park, car park etc. Can be used in conjunction with service=* to indicate the type of usage and with access=* to indicate who can use it and in what circumstances.|
|Highway link||Short connecting ways, like highway or round-a-bout entrances and exits and "Michigan turns".|
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:
- 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 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
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
All tier 1 cities should generally be connected by motorway and/or trunk roads.
- Ann Arbor
- Battle Creek
- Bay City
- Port Huron
- Traverse City
- Sault Ste Marie
- St. Ignace
- Toledo, OH
- Duluth, MN
- South Bend, IN
- Green Bay, WI
Long-distance routes classified as trunk (Lower Peninsula)
|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)
|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.|
- 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)