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Home >Maine's Transportation Systems >Classification of Highways >Federal Functional Classification of Highways

Federal Functional Classification of Highways

In simplistic terms, "functional classification" reflects a highway’s balance between providing land access versus mobility. Functional classification is the process by which public streets and highways are grouped into classes according to the character of service they are intended to provide. Generally, highways fall into one of four broad categories: principal arterials, minor arterials, collector roads, and local roads. Arterials provide longer through travel between major trip generators (larger cities, recreational areas, etc.); collector roads collect traffic from the local roads and also connect smaller cities and towns with each other and to the arterials; and local roads provide access to private property or low volume public facilities.

View the complete FHWA Functional Classification Guidelines, Concepts, Criteria and Procedures. (Offsite)


This is a picture of scales showing highway classification

Principal Arterial - Interstate

A series of continuous routes that have trip lengths and volumes indicative of substantial statewide or interstate travel. This classification is for highways designated as interstate and include I-95, I-195, I-295 and I-395. There are approximately 367 miles of Interstate highway in Maine.

Principal Arterial - Other Freeways and Expressways

These roads must be divided highway with partial (freeway) or full (expressway) control-of-access. They primarily serve through traffic and major circulation movements within federally-defined urban areas. An example is Route 1 in Brunswick between Main Street and Cooks Corner. There are 18 miles of this classification in Maine.

Other Principal Arterial

These are highways which provide long distance connections, but do not fit the two categories above. There are 962 miles in Maine and there are two subcategories: rural and urban.

  • Rural: Corridor movement suitable for substantial statewide or interstate travel between larger population centers (e.g., Route 3, Augusta to Belfast). Of the total mileage, there are 787 rural miles.
  • Urban: Routes which carry through traffic and most of the trips entering/leaving a federally-designated urban area. They provide continuity for all rural arterials that intercept the urban boundary (e.g., Western Ave. in Augusta or Brighton Avenue in Portland). There are 175 miles of this type.

Minor Arterial

This refers to a series of continuous routes (1,315 miles in Maine) that should be expected to provide for relatively high overall travel speeds with minimum interference to through movement, and are defined as two distinct types:

  • Rural: Form a network of 1,039 miles in Maine, in conjunction with the rural principal arterial system, with service characteristics that:
    • Link cities, large towns and other traffic generators (e.g., major resort areas) that are capable of attracting travel over long distances;
    • Integrate interstate and intercounty service;
    • Have spacing consistent with population density so all developed areas are within a reasonable distance from the arterial system;
    • Provide service to corridors with trip lengths and travel densities greater than those served by rural collector or local systems (e.g., Rt. 27 from Farmington to Sugarloaf Mtn. and to the intersection of Route 16 in Eustis or  Rt. 3 between Ellsworth and Bar Harbor).
  • Urban: Within a federally-designated urban area, these roads interconnect with and augment the urban principal arterial system. They distribute travel to geographic areas smaller than those of higher systems and there are 276 miles in Maine.  Examples are Hogan Road in Bangor, or Stone St. in Augusta from the East side rotary to Eastern Ave. (Rt. 17).


There are 5,955 miles of urban and rural collectors in Maine.

  • Rural: Generally serve travel of primarily intracounty rather than statewide importance and travel distances are shorter than arterial routes.
    • Major Collector Roads: (a) Serve county seats not on arterial routes, larger towns not directly served by higher systems, (b) link nearby larger towns, or cities, or with route of higher classifications, and (c) serve more important intracounty travel corridors which could connect consolidated schools, shipping points, important agricultural areas, etc. Of the total mileage, there are 3,247 miles in Maine. An example is Rt. 9 in Augusta from intersection of Rt. 17 to the intersection of Rt. 126 in Randolph.
    • Minor Collector Roads: Spaced consistent with population density to accommodate local roads within reasonable distance of collector roads. Provide service to smaller communities. Link locally important traffic generators with the arterial system. There are 2,229 miles in Maine. An example is Pond Road/Neck Road between Manchester and Litchfield.
  • Urban: Provide both land access and traffic circulation within urban residential neighborhoods and commercial and industrial areas in federally designated urban areas. Route density is much higher than in rural areas. There are 479 miles in Maine. Examples include Buck Street in Bangor next to the racetrack, or Hotel Rd. in Auburn from Rt. 122 near the L/A airport to the West Auburn Rd.

Local Roads

Provide access to adjacent land and provide service to travel over relatively short distances as compared to the higher systems (13,619 miles in Maine).

  • Rural: All rural roads not classified as principal arterial, minor arterial, or collector roads. There are 12,034 miles in Maine, e.g., Caribou Lake Road between Washburn and Caribou, or Flag Pond Rd. in Saco from Rt. 1 west to Rt. 112.
  • Urban: All urban streets in a federally-designated urban area that are not in one of the other higher systems. They permit direct access to land, route density is higher than in rural areas, and they connect to the higher systems. They also offer lower mobility and service and through-traffic movement is deliberately discouraged. There are 1,585 miles in Maine. Examples are Purington Avenue in Augusta between North Belfast Avenue and South Belfast Avenue, or Longfellow Ave. in Brunswick from Rt. 123 to Maine St.

Characteristics of Rural Arterial Highways

  • Long Distance
  • Higher Speeds
  • Higher Volumes of traffic - Mutlilane Facilities
  • Interstate Travel - Interstate System
  • Link Major Cities
  • Statewide and Intercounty Travel.
  • Area Service Coverage

Characteristics of Rural Collector Highways

  • Shorter Trips
  • Moderate Speeds
  • Lower Volumes of Traffic - Two Lane Facilities
  • Intracounty Travel
  • Serves:
    • County Seats

    • Larger Towns not on Higher System

    • Consolidated Schools

    • Shipping Points

    • Larger Manufacturing Areas

Characteristics of Rural Local Highways

  • Adjacent Land is Primary Function
  • Shortest distances
  • Low Speeds
  • Low Volumes
  • Roads not Falling into Higher Systems





6 - 12
15 - 25

20 - 25
5 - 10

65 - 75
65 - 80

This is an example of a highway classification

This page last updated on 6/27/13