Illinois/Highway Classification

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This page will provide guidance to IL mappers in consistently classifying highways according to the 2021 US Highway Classification Guidance standards.

Other Illinois-based editors are encouraged to engage on the discussion page here, on the OSMUS Slack, or anywhere else, in order to move toward a general consensus.

General Guidelines

Detailed Definitions of Highway Classes

For the Chicago metro area, see Chicago_Area/Highway_Classification

Local knowledge is required as a road may have the characteristics for a class, but locally needs to be upgraded or downgraded due to its local use - usually confirmed via IDOT Data.

Motorway

From the US Highway Classification page:

The top category, highway=motorway should only be applied to roadways that are either signed Interstate highways or have ALL of the following characteristics:

  • Grade separation
  • Limited access via on/off ramps
  • No at-grade intersections or traffic signals (although on-ramps may have traffic control devices)
  • Divided carriageways
  • Designed and maintained to support high speeds over long distances as part of an interconnected motorway network

In Illinois, there exist many roadways which exhibit motorway characteristics, but only for shorter distances. See, for example, the US 20 bypass around Freeport.

42°17′58.56″ N, 89°38′08.16″ W

Following the US Classification guidelines:

Roads which are disconnected from the motorway network, but briefly exhibit motorway-like characteristics for short distances (also known as "motorway islands"), should not be tagged as a motorway. In general, a disconnected motorway should have multiple grade-separated, controlled access interchanges over a significant distance, generally at least 2-10 miles, in order to be tagged as a motorway island.

For other roads which exhibit many, but not all, motorway characteristics, it is recommended to add expressway=yes.

Trunk

Trunk roads are critically important routes that provide connectivity between motorways and other trunk roads. Together, with motorways, provide connectivity between the major population centers of the state or adjacent states. Per the 2021 US Classification standards, a motorway/trunk should make a cohesive, sensible network by itself.

These may have "motorway" features in their construction (noted above), but it is not necessary throughout their entirety.

Examples:

  • US 20 between Rockford to Freeport [1]
  • US 51 between Bloomington and Decatur [2]
  • Palatine Road between IL 53 and I-294 [3]
  • Kingery Highway between I-290 to I-55 [4]

Primary

The main non-trunk/non-motorway interconnecting roads between large communities. These are often US highways, but state and county highways may also be classified as primary roads. These are often designed for high volume, high speed traffic over long distances.

Examples:

  • Most parts of US 150
  • Old/Historic Route 66
  • Towanda-Barnes Road in Bloomington
  • US 34
    • Exception: US 34 in Kendall County, between Orchard Road and IL 71, is downgraded to Secondary because speed and local use is severely reduced due to going through the downtown area of Oswego.

Secondary

The most common major intra-urban arterial roads, secondary roads in urban areas tend to extend long distances through multiple neighborhoods and have higher traffic volumes than lower ranked roads.

Examples:

Tertiary

Tertiary roads are generally minor arterial roads and tend to be smaller than secondary roads in volume and/or distance. Functionally, tertiary roads often link neighborhoods/subdivisions to nearby secondary and primary roads or serve as minor interconnecting links between secondary/primary roads. They generally have higher volume than Minor class.

Examples:

Minor/Unclassified

Minor roads do not primarily serve residential dwellings and they are designed for more use than a Service class or have more/higher connections than a service road. This is where local knowledge is imperative.

Examples:

  • Bristol Ridge Road, Kendall County technically has the characteristics of a Tertiary class, however it is downgraded to Minor due to low traffic volume as confirmed by IDOT.
  • The area west of Menards in Yorkville can be a good example. Marketview Drive, Carpenter Street, and Menard Drive have nearly identical physical characteristics. But Marketview Drive is upgraded to a Minor due to more connections and, thus, higher volume.
  • The Oswego Shopping Center on US 34 is a difficult example. The road heading southeast from Pearce's Ford is not named, yet it is 5 lanes wide, is traffic signal controlled, and has a high volume. So it should be upgraded to Minor class, then the roads it connects to should be Service class.

Residential

Residential roads primarily serve residential dwellings and are generally discouraged from being used as thoroughfares.

Service

Service roads can be tricky. They are generally unnamed (though they can have names), lower speed and lower traffic volume than a Minor class, yet provide more connections than a Driveway class. They should not have direct access to residential or business units, nor parking ability - it should be a moving route.

Examples:

  • Consider the area in front of Kendall 11, both roadways head west from 5th Street with similar access and similar physical characteristics. However, the road directly in front of the theater should be classed as a Driveway as it provides direct access and you could encounter stopped cars. The road north of the theater only provides access to various parking lots for multiple businesses, so it should be considered a Service class. Then, as that road continues west, it is downgraded to Driveway class as it is now no longer providing access to other places.

Driveway

Driveway roadways provide direct access to residential or business units. They are roads with very low speed, the potential to pull in to a parking spot, and a high chance of encountering standing, stopped, or parked vehicles.

Examples:

  • The northeast corner of IL 47 and US 34 contains a gas station and access to various businesses. Every access point and drivable area is classed as Driveway due to the reasons mentioned above.

Parking Aisle

This class should be reserved for parking areas where both nodes of the Parking Aisle roadway will end at Driveway classed roadways and do not provide direct access.

Examples:

  • This parking lot is mostly considered Driveway except for the two ways that only provide additional parking.

Drive-Through

This class should be for roadways that serve a commercial purpose via a window, drive up, car wash, or other method where the vehicle remains in use and the path is not intended to serve as a route through a parking lot. This can include pharmacies, fast food restaurants, car washes, banks, etc.

Alley

Important Populations Centers for Trunk/Motorway Network

In no particular order, the following populated places are considered large/important enough to include in Illinois' motorway/trunk network.

  • Chicago Metro Area
  • East Dubuque (for connectivity west to Dubuque, IA)
  • Rockford
  • South Beloit (for connectivity north to Beloit / Janesville, WI)
  • Moline / Rock Island
  • Peoria
  • Bloomington / Normal
  • Springfield
  • Champaign
  • Decatur
  • East St. Louis
  • Terra Haute, IN (not in IL, but the biggest population center between Springfield and Indianapolis, which is an important transportation corridor)
  • Mount Vernon
  • Marion (also Paducah, KY and Mount City to the south, for connectivity w/ KY and MO)
  • Effingham
  • Quincy
  • Galesburg
  • Macomb
  • Hannibal, MO (again, not in IL, but an important node just over the border, and needs to be considered)
  • Kankakee

Chicago Metro Area

For simplicity, we'll consider this to be Cook County and the "collar counties" surrounding it, including DuPage, Will, Lake, Kane, and maybe just a bit of McHenry and Kendall.

Most of this area is quite built up, but around the edges of the metro area, there are distinct centers of importance as well.

  • Chicago itself
  • Aurora
  • Naperville
  • Elgin
  • Waukegan
  • Joliet
  • O'Hare Airport (Not a populated place, but my goodness, if every highway in IL doesn't converge here)

IDOT Data

IDOT (Illinois Department of Transportation) maintains the authoritative datasets on motorways and numbered state routes in Illinois, as well as a host of other datasets about local roadways. While these do not directly translate to the OSM highway classification system, they can be useful in identifying important populations centers, especially those not already served by the interstate system.

IDOT FHWA Classification

IDOT classifies roads in the state according to the FHWA system. Current functional classes can be viewed at IDOT's IROADS web app.

Roads Feature Service

Annual Average Daily Traffic

AADT Feature Service

Traffic Counts viewer

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