Colorado/Highway Classification

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This page describes Colorado-specific determinations for implementing 2021 Highway Classification Guidance values. Before making major changes based on this guidance, please discuss with the local mappers and those who made the determinations in the first place.

Colorado Data Sources and References

CDOT Links

Other Sources

Colorado functional classification definitions

Colorado DOT defines several functional classifications based on how roads are used. The definitions are closely aligned with the US Highway Functional Classification but may vary depending on local context.


  1. Principal Arterials - Principal Arterials serve a large percentage of travel between cities and activity centers. Principal arterials are typically roadways with high traffic volumes and are the frequent route for intercity busses and trucks.
    1. Interstates
    2. Other Freeways and Expressways - Roadways in this category with full access control look similar to Interstates. By definition, Freeways are characterized by full access control with access points limited to on/off ramps and no at grade intersections. Expressways are more common in rural settings where at grade intersections are permitted to varying degrees depending on context. In general, these types of roadways favor mobility over access with this being truer for Freeways than Expressways.
    3. Other Principal Arterials - These roadways serve activity centers and provide a high degree of mobility. These roadways provide additional access to parcels and have at-grade intersections. Other Principal Arterials provide similar service in both urban and rural areas; the primary difference in urban areas is the quantity of arterials serving a particular urban area and radiate out from the urban center. Rural areas would typically be served by one Arterial.
  2. Minor Arterials
    1. Minor Arterials provide service for moderate length trips, serve geographic areas that are smaller than the Principal Arterial roadways, and have higher connectivity to the Principal Arterials. In urban settings, they interconnect and supplement the Principal Arterial system, connect communities, and may carry many bus routes. In rural settings, they are typically designed to provide higher travel speeds with minimum interference to the through movement.

Collector Roads and Streets

  1. Collector Roads and Streets. Collectors provide the connection from Local Roads to the Arterial systems. Collectors may be subdivided into Major and Minor Collectors in both the urban and rural areas. A major part of the rural highway system consists of two-lane collector highways. The rural collector routes generally serve travel of primarily intra-county rather than statewide importance and constitute those routes on which predominant travel distances are shorter than on arterial routes. An urban collector street is a public facility that includes the entire area within the right of way. The urban collector street also serves pedestrian and bicycle traffic and often accommodates public utility facilities within the right of way.
    1. Major Collector. Major Collectors are typically longer in length, have lower connecting driveway density, higher posted speeds, higher traffic volumes and may have more travel lanes than the Minor Collector.
    2. Minor Collector. Minor Collectors serve both land access and traffic circulation, penetrate residential neighborhoods for short distances, operate at lower posted speeds, and have signalized intersections, provide service to smaller communities not served by Arterials, and link locally important traffic generators with rural surroundings.

Local Roads and Streets

  1. Local Roads and Streets. Local Roads account for the largest percentage of roadways in terms of mileage and are typically designed to discourage through traffic. A local road or residential street primarily serves as access to a farm, residence, business, or other abutting property. Some such roads properly include geometric design and traffic control features more typical of Collectors and Arterials to encourage the safe movement of through traffic. On these roads, the through traffic is local in nature and extent rather than regional, intrastate, or interstate. Local Roads are typically classified by default; once all other roads have been classified as Arterial or Collector, the remainder are Local Roads.

Important Population Centers

Colorado DOT divides the state into "transportation planning regions" that share common transportation characteristics and are anchored by a limited number of communities that rely on the same transportation resources. There are 5 urban regions, and 10 rural regions. The regions are grouped below, with major cities or towns indicated.

Urban Regions
Region Major Communities
Pikes Peak Area Colorado Springs
Greater Denver Area Denver

Central City

North Front Range Fort Collins


Pueblo Area Pueblo
Grand Valley Grand Junction
Rural Regions
Region Major Communities
Eastern Limon


Southeast La Junta


San Luis Valley Alamosa


Gunnison Valley Gunnison


Southwest Durango

Pagosa Springs

Intermountain Glenwood Springs


Northwest Craig

Steamboat Springs

Upper Front Range Fort Morgan
Central Front Range Fairplay

Cañon City

South Central Walsenburg



Motorways should be tagged using the criteria set in United_States/Highway_classification. In Colorado, roads with a CDOT-designation of Interstate or Freeway, and some Expressways will meet the definition of a highway=motorway.

Aligns with the CDOT designations of:

  • Interstate
  • Principal Arterial - Freeways and Expressways (if the road includes ALL of the characteristics of a highway=motorway)
Interstate Highways
Name Length (mi) Location Route Relation
I-70 449 East-west across the state WB:


I-25 299 North-south across the state NB:


I-76 187 Northeast from Arvada to NE state line
I-225 12 Auxiliary route to I-25 in southeast Denver and Aurora, from I-25 to I-70
I-270 7 Runs concurrently with US 36 in Denver
CO and US Highways with Motorway Construction
Name Length Location Route Relation Notes
US 6 / West 6th Avenue Freeway West Denver/Lakewood
US 285 / West Hampden Avenue Freeway Southwest Denver/Littleton only, roughly I-25 to C470 and slightly beyond Most of this highway S/SW of C470 is not a motorway
C-470, E-470 and the Northwest Parkway (toll) Denver "beltway" C-470 (SH 470):


NW Parkway:

Parts of NW Parkway do not meet motorway construction, but most does.
CO 58 / Golden Freeway Spur connecting Golden to I-70
US 36 / Denver/Boulder Turnpike Denver to Boulder (concurrent with I-270 for part of the highway)
Peña Boulevard I-70 to E-470 and Denver International Airport (DEN)
CO 21 / North Powers Boulevard Colorado Springs Evaluate? Looks like it is turning into a motorway, but where does it connect to the network?
US 24 / East Fountain Boulevard Colorado Springs Evaluate? Looks like a too-small stub for a motorway?
South Academy Boulevard, Milton E. Proby Parkway and CO 115 Air Force Academy in Colorado Springs Evaluate? These are very small stubs, though the construction is motorway-like?
CO 47 East of Pueblo Evaluate? Small stub?

Trunk Roads

See United States/Highway classification#Trunk.

Trunk road (US 50) maintaining its tagging as it passes through a town, due to the high importance of the road. maxspeed=*, lanes=*, and other descriptive tags are used to indicate the change in road features inside the town.

"As the top non-motorway classification, highway=trunk should be applied in the following cases:

  • In areas of high population density, to expressways that meet most, but not all, of the requirements for highway=motorway, and provide connectivity between motorways and other trunk roads. These roads should also be tagged expressway=yes.
  • In areas of medium to low population density, to the most important non-motorway roads that provide principal, long-haul connections between population centers of regional importance."

The following roads are the principal routes between pairs of important population centers, and not serviced by highway=motorway, and thus should be tagged highway=trunk. If the road, or portions of the road have the physical characteristics of an expressway, then expressway=yes may be added to indicate the method of construction.

The trunk classification of these roads should terminate either at a motorway or at another trunk-classified road to ensure network continuity. The only exception to this rule is in the case of cities of regional importance where the sole principal trunk route terminates at a city due to terminal topography.

When a trunk road passes through a town or community, its importance to the road network means it should retain the trunk tag. Use other descriptive tags such as maxspeed=*, lanes=*, width=* to indicate the changes to the physical road construction inside the town. Exception: If there is a trunk or motorway level bypass that through-traffic is expected to use, then the portion of the original trunk that passes through down may be downgraded to primary.

Aligns with the CDOT designations of:

  • Principal Arterial - Freeways and Expressways (if not already a highway=motorway)
  • Principal Arterial - Other (unless parallel to another Principal Arterial or trunk)
Route From To Transportation Region Current Tagging Links Notes on Recent Changes
US 40 Dinosaur (UT state line) Kremmling Northwest trunk Trunk from state line to Kremmling. See below for decision on continuing trunk on CO 9 rather than US 40 south of Kremmling.
CO 9 Kremmling Silverthorne (I-70) Intermountain trunk CO 9 from Silverthorne to Kremmling has been proposed as a more important trunk route than US 40 from Empire to Granby. CODOT signage and the use of CO 9 as the I70 bypass over the last summer closures seems to support this, while traffic counts remain higher on US 40 - these higher traffic counts are likely due to Winter Park local traffic, rather than through traffic which stays on CO 9.
US 40 Limon (I-70) Kit Carson (US 287) Eastern trunk Upgraded to trunk.
CO 13 WY state line Rifle (I-70) Northwest primary Continue on WY 789 to I-80?
US 287 Laramie, WY Longmont Upper Front Range Mixed primary/trunk Upgrade whole section to trunk, including thru-connectivity in Fort Collins.
US 34 Estes Park Wiggins (I-76) Upper Front Range trunk Estes to Loveland/US 287 has been updated to trunk. US 34 from Fort Morgan to the Nebraska border has been downgraded to primary.
US 36 Estes Park Boulder Upper Front Range primary After reviewing the traffic data, it looks like it should be a trunk (serving many east-west corridors). Currently in discussion
CO 82 Glenwood Springs Aspen Intermountain trunk Trunk ends at Aspen, see below.
CO 82 Aspen US 24 Intermountain secondary Agreed that it should stay secondary - left here for discussion. Move to Exceptions later. Winter closures, length restrictions, etc. make it not suitable as a trunk.
US 50 KS state line Grand Junction Gunnison / Central Front Range / Southeast trunk
US 24 Buena Vista Minturn (I-70) Intermountain primary Up for discussion - Possibly trunk, though CO 115 has been proposed as the more important route out of CO Springs. East of CO Springs is a good candidate for trunk.
US 285 Denver Through Alamosa to Espanola, NM Central Front Range / San Luis trunk/primary Upgraded to trunk south of Alamosa and into NM, based on agreement with NM mapping community. North to Denver upgraded (phidauex). Up for Discussion - Salida to Alamosa - use US 285 or CO 17? Good argument for CO 17 (faster, more traffic).
US 550 Aztec, NM Montrose Southwest trunk/primary SB NB Construction south of Durango indicates expansion. 550 considered an important route by NM mappers.
US 160 Durango Walsenburg Southwest / San Luis trunk Upgraded to trunk (phidauex)
US 491 Cortez Monticello (UT) Southwest trunk
Consensus with UT and NM mappers is that this route qualifies as a trunk and has been upgraded.
US 287 Limon OK state line Eastern / Southeast trunk/primary Upgraded to trunk from Limon to Lamar, should extend to Boise City, OK.
US 24 Colorado Springs Limon Eastern / Pikes Peak trunk
US 385 Kit Carson / Cheyenne Wells Julesburg Eastern primary Possibly extend up to I-80?
CO 71 Limon Kimball, WY Eastern primary
CO 145 and 62 Cortez Ridgway Southwest primary

Lesser Road Classifications

highway=primary is used for the following roads not otherwise tagged as a higher classification (i.e. motorway or trunk):

highway=secondary is used for the following roads not otherwise tagged as a higher classification:

  • CDOT-designated Major Collectors
  • US and CO Highways not already tagged above

highway=tertiary is used for the following roads not otherwise tagged as a higher classification:

  • CDOT-designated Minor Collectors
  • Local roads which provide access to residential and/or industrial areas. As a rule of thumb, these roads are normally striped with a dividing center line, unless they are one-way. For roads which are striped for a portion of their length, mappers should use common sense in determining whether the road should be tagged tertiary. In the more rural areas of the state, it may be appropriate to tag un-striped or unpaved through-roads as tertiary if they provide through-connectivity through otherwise sparsely settled areas.
  • Tertiary and above would all be considered suitable for passenger cars. Lower classifications are often suitable for passenger cars, but certain smoothness=* or surface=* tags may imply 4WD-only conditions.
  • Example of an unpaved tertiary road: Kebler Pass Road

highway=residential is used for:

  • Minor, often un-striped or unpaved roads which provide terminal access to residential areas and do not provide primary through connectivity to the larger road network.

highway=unclassified is used for:

  • Minor, often un-striped or unpaved roads which provide terminal access to non-residential areas, do not meet any of the criteria for highway=service, and do not provide primary through connectivity to the larger road network.

highway=track is used for:

  • Minor land access roads that are not part of the general-purpose road network. Colorado track roads are typically unpaved, unmaintained or infrequently maintained, and do not serve homes, businesses or populated areas. The most common uses are forestry access, agricultural roads, old or historic mining access roads, and outdoor recreation access.
  • Important: Just because a road is dirt, or even two-track in construction, roads should still be tagged by their function first.
    • If the road serves homes, then it may be better tagged as highway=residential and surface=unpaved.
    • Likewise a road service an operating business or regularly operating mine or oil site may be better tagged as highway=service.
    • A road serving a single home or farmstead should not be tagged as a track, but instead as highway=service, service=driveway, surface=*. If the road continues beyond the home to general purpose agricultural buildings or just general access to the land, then that portion may be tagged as a track.
  • When tagging track roads, use physical attribute tags to better define the road. In CO some track roads may be generally passable by all vehicles, but some may be extreme 4WD trails. These tags help differentiate road quality:
    • surface=* specifies the surface material (paved, unpaved, gravel, dirt, etc).
    • tracktype=<grade1-grade5> specifies roadway firmness.
    • smoothness=* specifies physical usability by different types of wheeled vehicles.
      • Passenger car: intermediate or bad.
      • High clearance or light duty four wheel drive: very_bad.
      • Four wheel drive: horrible or very_horrible
    • width=* specifies the width of the track.
  • Track roads may be found on public or private land, and even those on public land may not be accessible to motor_vehicles. Usually these need to be tagged as motor_vehicle=no. Avoid the use of access=no unless all access (including foot travel) is prohibited. Use appropriate access=* tags to indicate whether the track is accessible to the public, or is private or otherwise restricted. Do not assume that a track is accessible simply because it is on State or Federal land. The Forest Service roads map layer and Motor Vehicle Use Maps may be useful for determining access rights. Please do not add a new track on public land with out first verifying it's access status and tagging it appropriately.
  • Some old double-track roads may now be in use exclusively for hiking, biking or equestrian activities, and are permanently closed to vehicular traffic. Judgement may be required on whether these should remain track roads, or be tagged as highway=path. Until further consensus develops on the topic, the recommendation is to stay with the existing classification. If a mapper believes a change is warranted on a particular segment, pay special attention to the physical attribute tags such as width so that the ability for a vehicle to traverse the road in an emergency is not obscured.
  • Please refer to the official wiki page on track roads, as well as the current 3rd draft of revised track language based on input from Colorado and other US mappers.

List of Exceptions

Statewide special cases

  • None identified yet.