Hierarchy of roads

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The hierarchy of roads.

The hierarchy of roads categorizes roads according to their functions and capacities. While sources differ on the exact nomenclature, the basic hierarchy comprises freeways, arterials, collectors, and local roads. In reality, streets (named or natural) are found to demonstrate scaling hierarchy, implying statistically that there are far more short (or less-connected) streets than long (or well-connected) ones, and subsequently a minority of streets account for a majority of traffic [1] The hierarchy can be simply derived through applying Head/tail Breaks, a new clustering scheme for data with a heavy-tailed distribution such as power laws and lognormal. The head/tail breaks is implemented in the free software Axwoman: http://fromto.hig.se/~bjg/axwoman/

The related concept of access management aims to provide access to land development, while ensuring traffic flows freely and safely on surrounding roads.

United States and Canada[edit]

Freeways[edit]

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.

Arterials[edit]

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 Britain) or they are just too short (superarterials in Nevada). Such roads are usually classified as arterials.

Frontage roads are often used to reduce the conflict between the high-speed nature of an arterial and property access concerns.

Collectors[edit]

Collectors (not to be confused with collector/distributor roads, which reduce weaving on freeways), collect traffic from local roads, and distribute it to arterials. Traffic using a collector is usually going to or coming from somewhere nearby.

Local roads[edit]

At the bottom of the hierarchy are local streets and roads. These roads have the lowest speed limit, and carry low volumes of traffic. In some areas, these roads may be unpaved.

United Kingdom[edit]

Motorway[edit]

Similar to freeways, these high-speed roads are designated with an M prefix or (M) suffix. e.g. M1, A1(M). The speed limit is generally 70 miles per hour (110 km/h) and there is a hard shoulder, an often slightly narrower lane next to lane 1, which is usually only to be used in cases of an emergency. Emergency telephones are located every mile along the route so motorists with broken-down vehicles can contact the authorities, although this is increasingly being done using mobile phones. Signs are blue with white text for both destinations and motorway numbers. In general, junctions are given numbers which are displayed prominently, sometimes with a letter suffix, in a small black box on all the signs for any given junction. Junctions are generally signed one mile before they exit, with three or four further signs as the junction is reached, although on busy urban stretches this first warning can reduce to about ⅓mile. Cyclists, pedestrians, mopeds, very slow vehicles and certain other traffic is banned.

Primary A-road[edit]

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. Some of the major dual carriageway primary routes have numbered junctions or hard shoulders in the style of the Continental semi-motorways. Many Primary Routes are largely or wholly subject to clearway restrictions, and in major cities they may be classed as red routes. Emergency telephones, if present at all, are usually infrequent - there may be some additional telephones operated by the UK's two main motoring organisations, the RAC and the AA, but these are becoming rarer.

Non-primary A-road[edit]

Often exists where the route is important but there is a nearby primary route (A or motorway) which duplicates this road's function. Shown as red on maps, and has white signage with black lettering. Some non-Primary A-class roads are partially subject to clearway restrictions.

B road[edit]

Regional in nature and used to connect areas of lesser importance. Usually shown as brown or yellow on maps and have the same white signs as non-Primary A-Class routes.

C road[edit]

C roads are used as local authority designations for routes within their area for administrative purposes. These routes are not shown on road maps, but have occasionally been known to appear on road signs.

Unclassified[edit]

Unclassified roads are local roads with no defined destination. Local destinations may, however, be signed along them.

France[edit]

Autoroutes[edit]

Along with the rest of Europe, France has Motorways or Autoroutes similar to the British network. Unlike in the UK, the network is mostly accessible on payment of a toll, which is usually distance-dependent; there are generally more Toll (péage) Motorways in the South of France. However, sections passing through or close to major towns and cities are usually free. As in the UK, destinations reached via a motorway are shown with white text on a blue background. Junctions are usually numbered, the numbers being shown on signs in a small oval in the corner of the sign.

Route Nationale[edit]

Before the building of the Autoroutes, the Routes Nationales were the highest classification of road. They are denoted by a route number beginning N, or occasionally, RN. Going back to a Napoleonic road classification system, these are main roads comparable with British Primary Routes. They are maintained directly by the state and are usually the shortest route between major centres. Many N-Class roads are dual carriageway for some or all of their length, with a few also being given the designation of semi-motorway, where junctions are grade-separated and there is a central reservation with crash barrier. The hard shoulder, or bande d'arrêt d'urgence, is often narrower than on full motorways and there are fewer emergency telephones.

Routes Départementales[edit]

France (including overseas territory) is split into 100 Départements, the second-highest tier of local government, similar to a UK county or US state. The Départements have responsibility for all roads beginning with a letter D, or occasionally RD. These roads vary in quality, from newly built local dual carriageways and downgraded Routes Nationales to winding roads that are barely wide enough for traffic to pass. Generally, they are quieter than the Routes Nationales, and of a reasonable standard.

Routes Communales[edit]

In general, each settlement in France is a Commune - akin to a British Civil Parish. This most local level of government is responsible for maintaining all the local roads, which are numbered with a letter C prefix. Except in major towns and cities, where their numbers are usually not marked on signs, they are usually single-track and may be in a state of poor repair due to the large number of roads covered by populations as small as 10.

Romania[edit]

In Romania the roads are classified as:

  • Autostrăzi (A) - Motorways
  • Dumuri naționale și europene (DN, E) - National and European roads
  • Dumuri naționale (DN) - National roads
  • Dumuri județene (DJ) - County roads
  • Dumuri comunale (DC) - Communal roads

Elsewhere in Europe[edit]

Most of Europe has adopted Motorways (Autoroutes/Autobahns/Autopistas/Autostrada), usually similar to those in France and the UK. The idea was originally developed in Germany, where all motorways are toll-free, and has spread widely. All major through routes in the EU and neighbouring countries have a European E-Road number in addition, or in the case of some countries' motorways, instead of a national number. In the UK these numbers are not displayed.

Otherwise, most other European countries have some form of differentiating between national routes, regional and inter-regional roads and other local routes.

References[edit]

  1. ^ Jiang, Bin 2009. "Street hierarchies: a minority of streets account for a majority of traffic flow",International Journal of Geographical Information Science, 23(8), 1033-1048.

See also[edit]

External links[edit]