Section 3: Functional Classification

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Functional classification is the grouping of roads, streets, and highways into integrated systems, each ranked by its importance to the general welfare, the motorist, and the land‑use structure. Functional classification is used to define the role any particular road should play in serving the principal functions of a road: mobility for through movements and access to adjoining land.

Importance. This functional grouping implies that roads have differing levels of importance based on their functions. Importance is based on economic and social values, which are measured in a variety of ways. However, the basic idea is the same regardless of the method of measurement: more important roads or more critical needs deserve the most attention. In the context of roads, that usually means more funding.

Without a classification system, it is difficult to compare roads fairly. For example, a high-volume through road has different needs than a dead-end street that serves a residential neighborhood. The neighborhood street is important mainly to the local residents, whereas the high-volume street is important to many people. If roads were ranked by importance to the most people, the local street would rarely get attention. With functional classification, the through road would be ranked with similar roads, and the local street would be ranked with other local streets. Both would then be considered for improvements, maintenance, etc. relative to competing projects on similar types of streets. In essence, functional classification allows for equal and equitable treatment where conditions are similar.

Background. Beginning with the passage of the Federal‑aid Act of 1921, functional classification concepts and criteria were used in the selection of the original federal‑aid highway system. This limited-mileage, interconnected system of highways, important to interstate and intrastate motor vehicle travel was later designated the Federal‑aid Primary System (FAP). The selection in the early 1940s of the original Federal‑aid Secondary System (FAS), an interconnected system of principal secondary and feeder roads, with unlimited mileage, was also based on functional concepts. The most significant event in the history of functional classification occurred in the later 1940s with the selection of the National Interstate Highway System. This system of interconnected routes, very limited mileage, and the highest design standards, was created to serve the economic, social, and defense needs of the nation.

In the Federal - aid Highway Act of 1973, Section 148, Congress specified that the classification of all streets and highways and the realignment of the federal-aid systems be based on anticipated functional usage in 1980. All surface transportation legislation passed since that time has included a mandate for use of a functional classification system.

Concepts. The entire concept of functional classification is based on certain key characteristics that can be used to differentiate between different kinds of highway facilities. First, urban and rural areas exhibit different characteristics — including the density and types of land uses, the density of street and highway networks, the nature of travel patterns, and the way that the highway network itself relates to these characteristics. Therefore, the functional classification scheme used throughout the nation provides separate classification systems for urban and rural facilities.

For clarity, urban areas are subdivided into two categories — urban and small urban. Urban areas are defined as population centers of 50,000 or more. Small urban areas begin at a population threshold of 5,000. This latter threshold was established based on observations that rural arterial and collector routes provide an adequate arterial street network in places of less than 5,000 population. Hence, rural classifications apply to roads in all areas of less than 5,000 population.

Second, functional classification differentiates between different types of highway service. The two most general types of highway service are mobility and land-use access. Arterials emphasize a high degree of mobility, high speeds for long trips, which means limited access. Local facilities emphasize the land-use function with low speeds and many access points. Collectors more-or-less serve both functions halfway.

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  • Federal-aid Highway Act of 1973, Section 148
  • Intermodal Surface Transportation Efficiency Act, 1991
  • Transportation Efficiency Act for the 21ST Century, 1998
  • Jack Foster Memo dated May 26, 1998
  • Jack Foster Memo dated June 15, 1998.
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Uses of Functional Classification

Some functional classification uses are to:

  • provide the framework of highways for creating mobility and connecting regions, cities, and ports within a state
  • provide a basis for assigning jurisdictional responsibility according to overall importance of the road
  • provide for minimum design standards according to function
  • provide a basis for evaluation of present and future needs
  • provide a basis for the apportionment of scarce fiscal resources.
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Characteristics of Different Functional Classes

Characteristics of different functional classes are given in detail in excerpts from “Highway Functional Classification Concepts, Criteria and Procedures.” To see the excerpts, click pln_ape. The complete document was last published by the U.S. Department of Transportation, FHWA, as a revision dated March 1989. Credit is also given to the “Statewide Highway Planning Procedures” course (National Highway Institute course #15127).

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Administrative Responsibility and Procedures

TPP has primary responsibility for implementing functional classification responsibilities for the department. This is accomplished by TPP staff working with the district staff who in turn are responsible for coordination with local elected officials and other planning entities (MPO, etc.).

By memos from Jack Foster dated May 26, 1998, and June 15, 1998, TPP furnished Functional Classification Request Guidelines. Requirements included:

  • memorandum from district describing changes
  • specific information:
    • name of facility
    • limits of the change
    • mileage of the change
    • type of change
    • functional map requirements
  • justification and documentation
  • MPO approvals
  • cooperation with local officials
  • urban boundary changes
  • mileages.

To see a PDF file of these Functional Classification Request Guidelines memos for reference and additional information, click pln_apf.

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