Functional Classification

Functional classification is an ordering system that defines “the part that any particular road or street should play in serving the flow of trips through a highway network.” Functional classification categorizes streets according to their ability to 1) move traffic and 2) provide access to adjacent properties. Street types under functional classification include “local streets,” medium-sized “collectors,” and highway-type “arterials.”

Many city streets predated the advent of the Federal Highway System of functional classification, making the system unsuitable for the diversity of land uses and travel characteristics throughout an urban area. While certain types of classification make streets eligible for highway aid, once a street is given a class, federal design standards that do not consider local context may be assigned to that street, and any variation requires a design exception.

Discussion

City streets are complex places where functional classification schemes—whether from a state agency or from the Federal Highway Administration—are generally too limiting as a basis for design capable of achieving social and economic goals for quality of life, mobility, and urban vitality. Such state or federal standards must be adapted to the urban environment before adoption so that city leaders maintain their flexibility to make streets a supportive element of a socially and economically thriving public realm.

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Many cities use some form of street classification to provide stakeholders and developers with a set of standard street cross-sections to guide new development and rehabilitation. These set requirements for the construction of the street as well as dimensions for sidewalks, curbs, and setbacks. Federally defined functional classes, which are generally applied to National Highway System streets, have associated design guidelines used by some cities as well.

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Even when they are completely updated, classification schemes, in and of themselves, are rarely adequate as a design tool for the diversity of situations to be encountered on city streets. Each project should also be approached with sound case-by-case professional judgment. In certain cases, cities may choose to alter a street’s classification level to better align with a community’s vision for its future.

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Updated street design standards should be consistent with citywide goals for safety, economic growth, development, and urban design. These standards should attempt to capture the unique local relationship between the built realm and the surrounding streetscape, encapsulating the varying scales at which motorists, bicyclists, and pedestrians interact with individual corridors as well as the overall street network. This entails requiring sidewalks on urban arterials, enhancing the quality of street construction for special districts, and controlling access points to the property to reduce conflicts between driveway traffic and pedestrians.

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Many cities have developed street classification systems specific to their local needs. These classification systems generally combine 2–3 variables that guide decision making:

• Street type and usage
• Urban design context and built environment
• Overlays, including modal priorities, special uses, and historic designations

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