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Highway Functional Classification Concepts, Criteria and Procedures

Section 1. Introduction

The Highway Functional Classification: Concepts, Criteria and Procedures, 2013 Edition, describes the procedures and processes for assigning functional classifications to roadways and adjusting urban area boundaries. This document builds upon and modifies prior guidance documents.

Our nation's roadway system is a vast network that connects places and people within and across national borders. Planners and engineers have developed elements of this network with particular travel objectives in mind. These objectives range from serving long-distance passenger and freight needs to serving neighborhood travel from residential developments to nearby shopping centers. The functional classification of roadways defines the role each element of the roadway network plays in serving these travel needs.

Over the years, functional classification has come to assume additional significance beyond its purpose as a framework for identifying the particular role of a roadway in moving vehicles through a network of highways. Functional classification carries with it expectations about roadway design, including its speed, capacity and relationship to existing and future land use development. Federal legislation continues to use functional classification in determining eligibility for funding under the Federal-aid program. Transportation agencies describe roadway system performance, benchmarks and targets by functional classification. As agencies continue to move towards a more performance-based management approach, functional classification will be an increasingly important consideration in setting expectations and measuring outcomes for preservation, mobility and safety.

As a result of the decennial census, the US Census Bureau issues urban area boundary maps. Transportation agencies should review these census boundaries and either accept them as is or adjust them for transportation planning purposes.

This guidance document provides recommended practices for assigning functional classifications and adjusting urban area boundaries concerning roadways that Federal, State and local transportation entities own and operate. Assigning functional classifications and adjusting urban area boundaries requires work elements common to many large-scale business enterprises: there are technical methods and tools to create an efficient and cost-effective end product; there are also procedural elements that require coordination and negotiation across agencies and individuals. This guidance document encompasses both of these elements.

This guidance document also recognizes and describes the implications of how our roadway systems are configured, used and planned for today:

1.1 Overview

This guidance document builds upon and updates the two most recent guidance documents circulated by FHWA, namely:

  1. All functional classification categories will now exist in both urban and rural areas. Specifically, all Principal Arterial sub-categories and all Collector sub-categories will be recognized in both urban and rural forms. The following revised functional classification categories should be used:
    1. Principal Arterial
      1. Interstate
      2. Other Freeways & Expressways (OF&E) (Figure 1-1)
      3. Other (OPA)
    2. Minor Arterial

      Photograph showing a two-lane expressway in an urban area

      Figure 1‑1: Principal Arterial - Other Freeways & Expressways

      Source: Ohio Statewide Imagery Program

    3. Collector
      1. Major Collector
      2. Minor Collector
    4. Local
  1. States should assign functional classifications according to how the roadway is functioning in the current year only. With regard to future routes, roads should be functionally classified with the existing system if they are included in an approved Statewide Transportation Improvement Program (STIP) and are expected to be under construction within the STIP timeframe of 4 years or less. Use the current classification for roadways, even replacement roadways that will upgrade the roadway, until construction is complete. Reclassify the new roadway once it has been constructed.

    Figure 1-2: HOV Lane on Interstate 95 in Woodbridge, VA

    Photograph of a three lane interstate facility with a barrier separated two-lane HOV facility.


Roadways that fall into the Principal Arterials- Other Freeways & Expressways category are limited-access roadways that serve travel in a similar way to the Interstates.

  1. Ramps and other non-mainline roadways are to be assigned the same functional classification as the highest functional classification among the connecting mainline roadways served by the ramp. (Figure 1-2)
  2. Principal Arterial roadways (Figure 1-3) serve a large percentage of travel between cities and other activity centers, especially when minimizing travel time and distance is important. For this reason, Arterials typically are roadways with high traffic volumes and are frequently the route of choice for intercity buses and trucks. The spacing of Arterials in urban areas is closely related to the trip-end density characteristics of activity centers in urban areas. The spacing of these facilities (in larger urban areas) may vary from less than 1 mile in highly developed central business areas to 5 miles or more in the sparsely developed urban fringes.

Figure 1-3: Other Principal Arterial in California

Photograph of an at-grade, two lane urban arterial, with sidewalks, shoulders and a signed bike lane.

Source: Akos Szoboszlay

Transportation agencies apply a variety of treatments to preserve mobility and increase the person throughput of Urban Arterials, including ramp metering, high-occupancy-vehicle (HOV) lanes and high-occupancy toll lanes.

Principal Arterials play a unique role in providing a high degree of mobility and carrying a high proportion of travel for long distance trips. These facilities carry the major portion of trips entering and leaving an activity center, as well as the majority of through movements that either go directly through or bypass the area.

Updated: 10/20/2015
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