National Functional Classification (NFC) is a planning tool which federal, state and local transportation agencies have used since the late 1960's. The Federal Highway Administration (FHWA) developed this system of classifying all streets, roads and highways according to their function. The FHWA publication, Highway Functional Classification: Concepts, Criteria and Procedures, provides the basis for much of the following information.

Principal arterials are at the top of the NFC hierarchical system. Principal arterials generally carry long distance, through-travel movements. They also provide access to important traffic generators, such as major airports or regional shopping centers.
EXAMPLES: Interstate and other freeways; other state routes between large cities; important surface streets in large cities.

Minor arterials are similar in function to principal arterials, except they carry trips of shorter distance and to lesser traffic generators.
EXAMPLES: State routes between smaller cities; surface streets of medium importance in large cities; important surface streets in smaller cities.

Collectors tend to provide more access to property than do arterials. Collectors also funnel traffic from residential or rural areas to arterials.
EXAMPLES: County, farm-to-market roads; various connecting streets in large and small cities.

Local roads primarily provide access to property.
EXAMPLES: Residential streets; lightly-traveled county roads.

All questions can be sent to: mdot-nfc@michigan.gov