Table of Contents

Background

Functional classification identifies the role a highway or street plays in the transportation system. Some highways are intended to emphasize mobility for longer-distance trips, while other roads are intended to primarily provide access to land. Planners and engineers have developed functional classification categories based on access and mobility, the types and lengths of trips that are accommodated, and surrounding development intensity – rural or urban.  

Functional classification informs roadway design decisions that affect the road’s function like roadway speed, width, and intersection spacing and control. Functional classification can also be considered when identifying the multimodal role of a road, including truck, bus transit, bicycle, and pedestrian use and accommodation. Highway and street projects should implement designs (including multimodal accommodations) that are compatible with a road’s functional classification and surrounding land uses. 

The main functional classes used in the metropolitan area are used nationwide and described in the Federal Highway Administration’s (FHWA) Highway Functional Classification Concepts, Criteria and Procedures, 2023 Edition. They consist of urban and rural designations for four main classes of roads: principal arterials, minor arterials, collector roads, and local roads. Although the FHWA designations are officially used at the state and federal level, the Met Council also applies sub-designations to minor arterials within the seven-county metropolitan planning area based primarily on land use type. The regionally identified sub-designations for the minor arterial network further refine the role the route makes within the Twin Cities region. 

Federal guidance allows use of federal funds on roads classified down to minor collectors in urban areas and major collectors in urban areas, but our region has chosen to use these scarce funds on the most important regional highways, which include the principal and minor arterials. 

Summary of Contents

This section of the Transportation Policy Plan identifies criteria and characteristics for use in assigning roadway functional classification. Criteria are the primary tool for identifying roadway function. Characteristics are intended to be guidelines if a roadway does not clearly fall into a single category. They are also useful when plans are being developed for constructing a new roadway or reconstructing a classified route.  

Functional classification system criteria are presented in Tables 5.1, 5.3, and 5.6. Functional classification system characteristics are shown in Tables 5.2, 5.4, 5.5, and 5.7. 

This section also includes a summary of Minnesota Department of Transportation (MnDOT) intersection spacing and control guidelines for federal, state, and interstate highways in the metropolitan area. The MnDOT access management guidelines were developed for the entire state; MnDOT’s functional classification category for the metropolitan area is summarized in Table 5.8 and on MnDOT’s Access Management web page. 

Figure 5.1: Map of functionally classified roadways

Functional Classifications

Principal arterials

The emphasis of principal arterials is on moving large volumes of traffic over long distances rather than providing direct access to land. They connect the region with other areas in the state, the nation, and North America. Principal arterials connect regional job concentrations and freight terminals within the metropolitan area. Principal arterials should support the longest trips in the region, including intercity bus, express bus, and highway bus rapid transit services.

Principal arterials consist primarily of interstate freeways, other freeways, and highways. Most principal arterials are owned and operated by MnDOT, but some are under the jurisdiction of Anoka, Dakota, Ramsey, and Scott counties or the City of Saint Paul. The Metropolitan Highway System, as defined in the Imagine 2050 Transportation Policy Plan, comprises all principal arterials in Anoka, Carver, Dakota, Hennepin, Ramsey, Scott, and Washington counties.

Principal arterial spacing and access spacing vary based on the density of surrounding development. Table 5.1 shows principal arterial spacing varies from 2 to 3 miles in the most densely developed parts of the region, to 6 to 12 miles in rural areas. Where an urban or suburban level of development is planned, spacing of principal arterials or future principal arterials may be two to three miles. Table 5.1 also shows access spacing to principal arterials; non-interstate freeways provide land access somewhat more frequently than interstate freeways. Principal arterials primarily connect to other principal and minor arterials. In the future, new connections to principal arterials should be limited to other principal and minor arterials.

Principal arterials are not intended to provide on-road facilities for pedestrian and bicycle travel. However, in cases where principal arterials are built through wide rights-of-way, shared-use paths separated from the roadway can be designed to safely accommodate pedestrian/bicycle travel along the principal arterial. Such parallel facilities can provide more efficient connections between major destinations for these modes. Where long, continuous rights-of-way are not available, even short trail segments can help to close system gaps. 

Principal arterials often act as barriers to bicycle and pedestrian travel in the centers and neighborhoods through which they pass. For nonfreeway principal arterials where bridge or underpass crossings are not feasible, roadway at-grade crossings must be carefully designed to safely accommodate pedestrians and bicyclists of all ages and abilities.

Minor arterials

The minor arterial system supplements the principal arterial system and provides connections to the principal arterial system. Minor arterials support access to major traffic generators, including regional job concentrations and freight terminals, and between rural centers within and just outside the region. Minor arterials should serve medium-to-short trips, including arterial bus rapid transit, limited-stop bus, and local bus service.

In the urban area the emphasis of minor arterials is on supplementing principal arterial mobility as opposed to providing direct access to land, and only concentrations of commercial, industrial, or residential land uses should have direct access to them. Minor arterials should connect to principal arterials, other minor arterials and collectors, although connections to some local streets are acceptable.

The spacing of minor arterials and access along them vary based on the density of surrounding development. Table 5.3 shows minor arterial spacing varies from one-fourth mile to three-fourths mile in the most densely developed parts of the region, to every one to two miles in the emerging suburban areas. Where an urban or suburban level of development is planned, minor arterials should be spaced every one-half mile to two miles. The criteria and characteristics in Table 5.3 and Table 5.5 apply to all minor arterials. The minor arterials are further assigned a sub-designation into one of the following four categories: Augmentor, Reliever, Expander, and Connector, and are described in Table 5.4. 

Minor arterials are designed to carry higher volumes of general traffic than other local roads and these design characteristics can create a barrier for bicycle and pedestrian travel. Priority should be placed on addressing these barriers in areas with pedestrian traffic, such as within regional job concentrations, within local centers, and along major transit routes.

Collector Roads

Mobility and land access are equally important on the collector road system. The collector system provides connections between neighborhoods and from neighborhoods to regional job concentrations and local centers. Collector roads also provide supplementary connections between major traffic generators within regional job concentrations. Direct land access should primarily be to development concentrations. Connectors typically serve short trips of one to four miles. Collectors connect primarily to minor arterials, other collectors, and local streets.

Major and minor collectors should be identified. Major collectors offer more mobility and minor collectors offer more access. Major collectors serve higher-density residential areas (often penetrating residential neighborhoods for significant distances), job and activity centers and freight terminals that are not on the arterial system, and they serve longer local trips, including local bus service. Minor collectors serve shorter local trips and lower-density land uses (often penetrating residential neighborhoods only for a short distance).  

Spacing of collectors in regional job concentrations and local centers may vary from one-eighth to one-half mile. In urban and urban edge communities, collectors are generally needed one-fourth to three-fourths a mile apart. In communities with suburban designations, spacing may range from one-half to one mile and may service existing development, but one-fourth to three-fourths mile spacing may be required in the future. Major collectors should be spaced farther apart than minor collectors.

Collector roads can be good candidates for bicycle routes because they serve shorter trips that bicyclists make and generally have more compatible traffic speeds and volumes as compared to arterials. Collectors in the urban area should include pedestrian accommodations and may be candidates for traffic calming, especially where pedestrian traffic is greatest, such as within regional job concentrations and local centers and along transit routes.

Local roads

Local roads connect blocks and land parcels, and the primary emphasis is on land access. In most cases, local roads connect to other local roads and collectors. In some cases, they connect to minor arterials. Local roads serve short trips at low speeds. In the urban center, local roads could be spaced as close as 300 feet, while in the rural area, one-mile spacing may be adequate. 

Local roads also serve travel for pedestrians and bicyclists. Transit is occasionally a consideration for local roads, depending on the surrounding land uses. 

Functional Classification System Criteria and Characteristics

Table 5.1: Functional Classification System criteria for principal arterials 

Table 5.2: Functional Classification System typical characteristics for principal arterials 

Table 5.3: Functional Classification System criteria for minor arterials 

Table 5.4: Minor arterial sub-designation characteristics 

Table 5.5: Functional Classification System typical characteristics for minor arterials 

Table 5.6: Functional Classification System criteria for collectors and local streets 

Table 5.7: Functional Classification System typical characteristics for collectors and local streets 

MnDOT Access Guidance

Table 5.8: Summary of MnDOT public street spacing access guidelines for interstate, U.S., and state highways in the Twin Cities metropolitan area

This table summarizes characteristics for existing roadways to be used in evaluating functional classification and should not be used as design guidelines. This table summarizes MnDOT Access Guidance for the metropolitan area and does not reflect all MnDOT guidance. Agencies should work with MnDOT, the appropriate county highway authority, and the local land use authority when planning new or modified access. Community designations are from Imagine 2050; they are not MnDOT designations.