Hierarchy of roads
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The hierarchy of roads organizes the functions of different types of roads. While sources differ on the exact nomenclature, in general they describe the same hierarchy.
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[edit] Freeways
At the top of the hierarchy are limited access roads freeways or motorways, including most toll roads. These roads provide largely uninterrupted travel, often using partial or full access control, and are designed for high speeds. Some freeways have collector/distributor lanes (also known as local lanes) which further reduce the number of access ramps that directly interface with the freeway, rather the freeway periodically interfaces with these parallel roadways, which themselves have multiple on and off-ramps. These allow the freeway to operate with less friction at an even higher speed and with higher flow. Often freeways are included in the next category, arterials.
[edit] Arterials
The next level are arterials. In general, arterials are major through roads that are expected to carry large volumes of traffic. Arterials are often divided into major and minor arterials, and rural and urban arterials.
In some places there are 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, dual carriageways in UK ) or they are just too short (superarterials in Nevada). Such roads are usually classified as arterials.
[edit] Collectors
These are followed by collectors (not to be confused with collector/distributor roads, which reduce weaving on freeways), which act to collect traffic from local roads and distribute it to arterials. Traffic using a collector is usually going to or coming from somewhere nearby.
[edit] Local roads
At the bottom of the hierarchy are local roads. These roads have the lowest speed limit, and carry low volumes of traffic. In some areas, these roads may be unpaved.
[edit] History
Roads have been distinguished by function probably since their beginning, and the hierarchy of roads was firmly established by the time of the Roman Empire.
[edit] Access management
The related concept of access management aims to provide access to land development while ensuring traffic flows freely and safely on surrounding roads. Frontage roads are often used to reduce the conflict between the high-speed nature of an arterial and property access concerns.
[edit] United Kingdom
While the above relates to the United States the UK has its own system.
Motorway - Same as freeway designated with an M prefix or (M) suffix. e.g M1, A1(M)
Primary A-road - Green on maps and signs. A main recommended route these can be either single carriageway or dual carriageway. The primary road network is fully connected, meaning you can reach any part from any other without leaving the network
Non-primary A-road - Often exists where the route is important but there is a nearby primary route (A or motorway) which duplicates this roads function. Shown as red on maps and with white signage
B road - Regional in nature and used to connect areas of lesser importance.
C road - Not officially signed or marked, C roads are used as local authority designations for routes within their area.
Unclassified - Local roads with no defined destination.
[edit] See also
[edit] External links
- FHWA - Functional Classification
- Florida Intrastate Highway System, an example of a statewide system of major arterials
