Functional classification is the process by which streets and highways are grouped into classes, or systems, according to the character of service they are intended to provide.
Most travel occurs through a network of interdependent roadways, with each roadway segment moving traffic through the system towards destinations.
The concept of functional classification defines the role that a particular roadway segment plays in serving this flow of traffic through the network.
Roadways are assigned to one of several possible functional classifications within a hierarchy according to the character of travel service each roadway provides.
Planners and engineers use this hierarchy of roadways to properly channel transportation movements through a highway network efficiently and cost effectively.
All functional classification categories now exist in both urban and rural areas and include:
A. Principal Arterial
ii. Other freeways and expressways
B. Minor Arterial
i. Major collector
ii. Minor collector
Why Do We Have It?
Federal functional classification began with the passage of the Federal Aid Act of 1921.
It established a federal aid primary system and, more importantly, the foundation for a system of national defense roads, later known as the national interstate system.
The absence of uniformity among states hindered federal efforts to determine national needs.
Subsequently, the Federal Aid Highway Act of 1973 mandated the realignment of federal aid roads on the basis of a standardized functional classification system. This process remains in effect today.
Who Maintains the Functional Classification System?
The Virginia Department of Transportation's (VDOT) Transportation and Mobility Planning Division (TMPD) is responsible for maintaining the commonwealth’s official federal functional classification system.
TMPD determines the functional classification according to federal guidance that takes into account type of trips, expected volume, what systems the roadway connects and whether the proposed functional classification falls within the mileage percentage thresholds established by the Federal Highway Administration (FHWA).
A statewide review of functional classifications typically occurs following the decennial census.
The most recent statewide update was completed and approved by FHWA in 2014.
For more information on functional classification criteria, reference: Functional Classification Comprehensive Guide
How Does VDOT Use Functional Classification?
Functional class impacts several factors including:
- Determining road design features. Applicable geometric design standards of the VDOT Road Design Manual (which adopts the American Association of State Highway Transportation Officials' (AASHTO) 2011 Green Book’s design level-of-service guidance on pages 2 - 66 and 2 - 67), as well as local and / or Subdivision Street Requirements relating to 24 VAC 30-91, collector or arterial standards.
- The eligibility of federal transportation funds for road improvements and maintenance.
- The frequency of VDOT maintenance inspections and prohibitions on vehicle parking on certain roads to reserve through lanes for peak period use.
- Development and /or maintenance of local roads, which are ineligible for federal funding and responsibilities, for this class of roads are private, local and / or state government concerns.
- Access management features (spacing-frequency and / or type of access such as interchanges, intersections, and roadside entrance, exit and / or driveway points).
- Eligibility for traffic calming measures.
- Data-record group types, such as mileage table records for certain road classes.
For questions regarding the Functional Classification System in Virginia contact:
Senior transportation planner
Long-range Planning Section manager