NCHRP Report 855, An Expanded Functional Classification System for Highways and Streets, presents an expanded functional classification system for highways and streets that builds upon the current system to provide a better basis for the preliminary engineering of a design project, including developing the purpose and need. In particular, it provides additional contexts beyond urban and rural, facilitates accommodation of modes other than personal vehicles, and adds overlays for transit and freight. Two case studies illustrating application of the expanded system to actual projects are included. The report will be useful to planners and designers and could be useful when developing preliminary designs. A careful agency review is recommended to ensure that the system is well suited to the agency’s particular circumstances.

 

Since 1984, the AASHTO “Green Book” (A Policy on the Geometric Design of Highways and Streets) and other roadway design criteria have been based on a functional classification system of a hierarchical network composed of arterials, collector roads, and local roads. This classification is further broken out by an urban or rural designation. This system is described in Highway Functional Classification Concepts, Criteria and Procedures (FHWA-PL-13-026). This system of highway classification has been under increasing scrutiny and discussion because of some incompatibilities with context-sensitive design, practical design, and other innovative approaches. The following are some concerns:

·         Designation as urban or rural is insufficient to adequately account for the range of contexts for a highway or street.

·         The current system is focused on the needs of vehicle drivers and does not help in serving the needs of other types of users (e.g., transit riders, pedestrians, bicyclists). In particular, it does not help with design decisions that must balance benefits for one mode against disbenefits for another (e.g., narrower lanes that benefit pedestrians but make it harder for trucks to use the road).

·         Classification leads to recommended or limited design choices that may not be optimal for the particular facility. These restrictions promote “designing to standards” rather than a careful consideration of the safety, operational, and other impacts of design decisions.

·         The public often questions the use of these classifications as the basis for design decisions.

 

In NCHRP Project 15-52, the University of Kentucky and Nelson\Nygaard reviewed the current functional classification system as well as alternative systems that have been used by transportation agencies internationally. Strengths and weaknesses were assessed to inform the development of a composite system that better meets the needs of planners and designers. Lastly, possible impacts on other uses of the current functional classification system were assessed (e.g., project funding, federal reporting) to prevent unintended consequences. For more information on the research performed, please see NCHRP Web-Only Document 230: Developing an Expanded Functional Classification System for More Flexibility in Geometric Design.