Editing Road hierarchy (section)

== United States  ==
[[File:Us-vmt-by-functional-system.png|thumb|440px|[[Vehicle miles of travel]] by highway functional system in the US]]

The U.S. [[Federal Highway Administration]] defines the following [[functional classification]] hierarchy:{{efn |Highway Functional Classification Concepts, Criteria and Procedures,<ref name="fhwa-functional-classification">{{cite book |author=FHWA |author-link=Federal Highway Administration |date=February 2023 |location=Washington, D.C. |title=Highway Functional Classification Concepts, Criteria and Procedures |url=https://www.fhwa.dot.gov/planning/processes/statewide/related/hwy-functional-classification-2023.pdf |edition=2023 |publisher=FHWA |archive-url=https://web.archive.org/web/20231025033059/https://www.fhwa.dot.gov/planning/processes/statewide/related/hwy-functional-classification-2023.pdf |archive-date=25 October 2023 |access-date=20 April 2025}}</ref> pp. 2, 19, 23, 24.}}

* '''Arterials'''
** '''Principal''' arterials
*** '''[[Controlled-access highway]]s'''
**** '''Interstate''' highways
**** '''Other''' freeways and expressways
*** '''Other''' principal arterials (with [[Limited-access road|partial]] or no access control)
** '''Minor''' arterials
* '''Non-arterials'''
** '''Collectors'''
*** '''Major''' collectors
*** '''Minor''' collectors
** '''Local''' roads and streets

The [[American Association of State Highway and Transportation Officials]] defines the following functional [[Geometric design of roads|design types]]:{{efn |"Functional Classification as a Design Type". A Policy on Geometric Design of Highways and Streets.<ref name="aashto-functional-classification">{{cite book |author=AASHTO |author-link=American Association of State Highway and Transportation Officials |date=2018 |chapter=Functional Classification for Motor Vehicles |location=Washington, D.C. |title=A Policy on Geometric Design of Highways and Streets |edition=7th |isbn=978-1-56051-676-7}}</ref>}}
* Freeways
* Arterials
* Collectors
* Local roads and streets

[[arterial road|Arterials]] are major through roads that are expected to carry large volumes of traffic. At the top of the mobility-access continuum, they include [[freeway]]s, whose on- and off-ramps enable operating with less friction at a high speed with high flow. In some places, arterials include large divided roads with few or no driveways that cannot be called freeways because they have occasional at-grade intersections with [[traffic lights]] that stop traffic (expressways in [[California]], which are [[limited-access roads]]) or they are just too short (superarterials in [[Nevada]]). [[Frontage road]]s are often used to reduce the conflict between the high-speed nature of an arterial and property access concerns.

[[collector road|Collector]]s, collect traffic from local roads, and distribute it to arterials. Traffic using a collector is usually going to or coming from somewhere nearby. They should not to be confused with [[collector lane]]s, which reduce [[Grade separation#Weaving|weaving]] on freeways.

At the bottom of the mobility-access continuum are local [[Street|streets]] and [[road]]s. These roads have the lowest speed limit, and carry low volumes of traffic. In some areas, these roads may be unpaved.