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Transportation: Plans & Programs: Federal Aid Functional Classification


Most travel in the United States occurs through a network of interdependent roadways, with each roadway segment moving traffic through the system toward their respective destinations. The concept of functional classification defines the role that a particular roadway segment plays in moving traffic through the network. Roadways are assigned to one of several possible functional classifications within a hierarchy according to the character of travel service that each roadway provides.

Transportation Function of Roadways

Roadways serve two basic transportation functions: mobility and access. These two functions are inherently at each end of the roadway spectrum.

Mobility provides few opportunities for entry and exit of the roadway, therefore limiting travel resistance created from vehicles entering and exiting the system. An example of a high mobility roadway would be the Interstate Highway System or other freeways and expressways.

Accessibility provides many opportunities for entry and exit of the system and therefore creates more travel resistance from an increased amount of vehicles entering and exiting the system. Examples of roadways that provide a high level of accessibility include collectors, and local streets. 

Other factors to be considered when assigning functional classification to a roadway include:

  • Efficiency of Travel
  • Access Points
  • Speed Limits
  • Route Spacing
  • Usage (Average Annual Daily Traffic {AADT} and Vehicle Miles of Travel {VMT})
  • Number of Travel Lanes
  • Regional and Statewide Significance

There are seven Federal Functional Roadway Classifications:

  • Interstate Highways – highest classification of arterials and were designed and constructed to increase mobility and accommodate long-distance travel
  • Other Freeways and Expressways - like Interstates, these roadways are designed and constructed to maximize their mobility function, and abutting land uses are not directly served by them
  • Other Principal Arterials - serve major centers of metropolitan areas, provide a high degree of mobility and can also provide mobility through rural areas. Unlike their access-controlled counterparts, abutting land uses can be served directly
  • Minor Arterials - provide service for trips of moderate length, serve geographic areas that are smaller than their higher Arterial counterparts and offer connectivity to the higher arterial system.
  • Major and Minor Collectors - serve a critical role in the roadway network by gathering traffic from Local Roads and funneling them to the Arterial network. Generally, Major Collector routes are longer in length; have lower connecting driveway densities; have higher speed limits; are spaced at greater intervals; have higher annual average traffic volumes; and may have more travel lanes than their Minor Collector counterparts
  • Local Access Roadways - are not intended for use in long distance travel, except at the origin or destination end of the trip, due to their provision of direct access to abutting land. They are often designed to discourage through traffic.



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The National Highway System (NHS)

The National Highway System consists of roadways important to the nation's economy, defense, and mobility. The National Highway System (NHS) includes the following subsystems of roadways (note that a specific highway route may be on more than one subsystem):

  • Interstate : The Eisenhower Interstate System of highways retains its separate identity within the NHS.
  • Other Principal Arterials: These are highways in rural and urban areas which provide access between an arterial and a major port, airport, public transportation facility, or other intermodal transportation facility.
  • Strategic Highway Network (STRAHNET): This is a network of highways which are important to the United States' strategic defense policy and which provide defense access, continuity and emergency capabilities for defense purposes.
  • Major Strategic Highway Network Connectors: These are highways which provide access between major military installations and highways which are part of the Strategic Highway Network.
  • Intermodal Connectors: These highways provide access between major intermodal facilities and the other four subsystems making up the National Highway System. A listing of all official NHS Intermodal Connectors is available here

The National Highway System (NHS) includes the Interstate Highway System as well as other roads important to the nation's economy, defense, and mobility. The NHS was developed by the Department of Transportation (DOT) in cooperation with the states, local officials, and metropolitan planning organizations (MPOs).

Pennsylvania NHS Map

Pittsburgh Urbanized Area NHS Map

Monessen Urbanized Area Map

Uniontown-Connellsville Urbanized Area Map

Maintenance and Updating of the Functional Classification System

Typically in southwestern Pennsylvania, the functional classification system is reviewed and updated every ten years to coincide with the decennial census and the adjusted urban boundary update cycle. However, in situations when a major land use change takes place or a new roadway is constructed, conditions are reviewed and updated as needed. The review and update of the functional classification system involves close coordination with PennDOT and local planning partners.

For more information on highway functional classification concepts, criteria and procedures for designating and changing a roadway’s functional classification, please refer to the U.S. DOT’s Highway Functional Classification Concepts, Criteria and Procedures Guide Book (2013)

Federal Functional Classification Maps for the SPC Region and the Commonwealth as a whole can be found here: http://www.dot.state.pa.us/Internet/Bureaus/pdPlanRes.nsf/infoBPRfunctionalclassmaps

Non-State Federal Aid Network

The U.S. DOT Federal-Aid Highway Program supports state highway systems by providing financial assistance for the construction, maintenance and operations of a 3.9 million-mile highway network throughout the nation. This network of roads is commonly referred to as the “Federal Aid System” and comprises approximately 5,840 miles in the SPC region.  The Federal aid system includes the Interstate Highway System, primary highways, and some secondary/local roads. Roads on this system are eligible to utilize funds from the Federal-Aid Highway Program to reimburse roadway owners for construction, operation, and maintenance projects. 

The overwhelming majority of the roads on the federal aid system in the SPC region are owned by PennDOT, however there is significant mileage that is not owned by PennDOT, which is referred to as the Non-State Federal Aid System.  SPC maintains a web portal to provide resources, data, and mapping pertaining to the non-state federal aid system. Portal found here: http://www.spcregion.org/trans_plan_nonstate.asp

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Southwestern Pennsylvania

Two Chatham Center Suite 500
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