Federal Aid Network

The Federal Aid Network includes the roads that are eligible for federal funding.  Sources of federal funding, including the Surface Transportation Block Grant (STBG), restrict eligibility to roads that are within the federal aid network.  These restrictions also extend to other state funding programs, such as the ADOT Highway User Revenue Fund (HURF).

Funding eligibility varies based on a road's federal functional classification and whether it is located within an urban or rural area.

• Urban Roads: Roads that are classified as urban minor collectors or higher (federal functional class 1-6) are eligible for federal aid

• Rural Roads: Roads that are classified as rural major collectors or higher (federal functional class 1-5) are eligible for federal aid

To learn more about federal functional classification, view its glossary page.  To learn more about urban and rural designations, scroll down to the Urban vs Rural Areas section of this page.

Urban areas are defined by the U.S. Census Bureau.  According to their definition, an urban area is comprised of a densely settled core of census blocks that, in addition to other criteria, have a minimum of 2,000 housing units or have a population of 5,000 people.  Visit the U.S. Census Urban and Rural website for more details.  As of 2023, Arizona has 57 Census urban areas.

The U.S. Census releases new urban area boundaries every 10 years, soon after they release the results of their decennial census.  Since the census urban boundaries do not account for features important for transportation planning, the Federal Highway Administration (FHWA) allows states to expand, or smooth, the census urban boundaries.  These smoothed boundaries are used by ADOT to determine whether a road is urban or rural for funding eligibility.