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.
Basic to this process is the recognition that individual roads and streets do not serve travel independently in any major way, but serve as part of an overall network.
Most travel involves movement throughout the network of roadways.
It becomes necessary to determine how this travel can be channelized within the network in a logical and efficient manner.
Functional classification defines the nature of this channelization process by defining the part that any particular road or street should play in serving the flow of trips through a highway network.
Why Do We Have It?
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 of the road by 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).
How Does VDOT Use Functional Classification?
Functional class impacts several factors including:
- Functional classification determines 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.