Science Fair Project Encyclopedia
A motorway (United Kingdom, Republic of Ireland, New Zealand, and some Commonwealth nations) is both a type of road and a classification. Motorways may also be regarded as highways designed to carry a large volume of traffic where a normal road would not suffice or would be unsafe, usually between cities. In the UK they are predominantly dual-carriageway roads, usually with three lanes in each direction although four-lane and two-lane carriageways are also common, and all have grade-separated access.
For a road to be classified as motorway a number of conditions must be fulfilled. The following conditions apply in the UK and the Republic of Ireland (though most of these rules are occasionally broken):
- Motorways must be accessed at junctions by slip roads off the sides of the main thorough-fare;
- Separate motorways are joined by link-roads at an interchange, the object of which is to allow traffic to change route without stopping or slowing significantly;
- Traffic lights are not permitted (except at toll booths and certain small interchanges);
- The central reservation must remain unbroken (a noted exception being the Aston Expressway in Birmingham, which has none);
- Emergency phones must be provided at a regular distance;
- The start and end of a motorway must have signposted entry and exit points;
- Certain types of transport are banned, typically: pedestrians, bicycles, learner drivers, horses, agricultural vehicles, underpowered vehicles (e.g. small scooters, invalid carriages).
- A 'minimum speed limit' may apply.
Note that these only apply to roads directly designated as motorways. Roads may also be indirectly designated as such, see #Inheritance below.
The construction and surfacing of motorways is generally of a higher standard than conventional roads, and maintenance is carried out more frequently; in particular, motorways drain water very quickly to reduce hydroplaning. Many roads in the UK and the Republic of Ireland are of near-motorway quality, but are not classified as such (generally for breaking one or more of the above rules). These are referred to as dual carriageways, which in Britain usually have the same 70 mph limit (the Irish limit is the regular 100 km/h (62.5 mph) limit). They may be subject to a lower speed limit (e.g. in urban areas).
In both countries, motorways are denoted by blue signage (and an M-prefixed road number). Speed limits are generally higher than on ordinary roads, with an overall limit of 70 mph (113 km/h) for cars in the UK. Some types of vehicle may be subject to a lower limit, while often sections of motorway are subject to lower speed limits due to local driving conditions. Lanes closest to the edge of the road are intended for general driving – these are hence the "inside" lanes, while the lanes closest to the median are intended for overtaking (passing) slower moving vehicles – hence they are termed "outside" lanes.
Roads in the Republic of Ireland have had metric speed limits since 20 January 2005 to conform both to European convention and to existing directional signage (which has long shown metric distances). The new speed limit introduced for motorways is 120 km/h (~75 mph).
The Conservative Party have proposed increasing the UK motorway speed limit to 80 mph, should they get into power at the next election. Many road safety groups feel this would be a good idea, as it more closely represents the normal (and, they claim, safe) driving practice of the majority of motorway users.
As in Germany but unlike in some other countries, drivers are not permitted to pass on an inside lane (a lane farther from the median) unless traffic in the 'faster' lanes is stationary. With a touch of black humour, the practice is popularly known as undertaking.
The road surface is generally asphalt ('black top') or concrete ('white top'). White dashed lines denote the lane separation, while an unbroken white line is painted alongside the median (usually known as the 'central reservation'). A white line (or in the Republic of Ireland, a yellow line) on the edge of the slow lane marks the edge of the hard shoulder. The hard shoulder is not used for traffic and is reserved for breakdowns or emergency manoeuvres. Generally lanes closer to the centre of the road (outer lanes) are used for overtaking, while lanes near the edge of the road (inner lanes) are used for slower traffic (see diagram on right). In the UK lanes in a given direction are numbered from left to right as lane 1, lane 2, lane 3, etc.
Other features are crash barriers , cat's eyes and increasingly, textured road markings (a similar concept to rumble-strips). In the UK it is a requirement that all motorways have emergency telephones at regular (usually one-mile) intervals which connect directly to the police.
The most basic motorway junction is a two-lane flyover with four slip-roads, two on each side of the motorway to exit or enter. A simple crossroads or roundabout is present on either end of the flyover. A rather large version of a roundabout, using two curved flyovers is sometimes used to present a single large junction for users of the slip-roads or crossing road. The slip roads leading off the motorway are known as 'exit sliproads', those leading onto the motorway as 'entry sliproads'. The precise sliproad at any junction may be identified by reference to the direction of the carriageway, for example 'northbound entry slip'.
An Irish invention is the signal-controlled roundabout which is often used in these situations. A further degree of complexity is present in Britain with varying types of Spaghetti Junction style interchanges.
Location and construction
Major intercity or national routes are often built or upgraded to motorway standard. Motorways are also commonly used for ring roads around cities or bypasses of built-up areas. Examples of ring-road motorways are the M25 around London and the M50 around Dublin.
In Britain there are plans to improve many motorways as well as to upgrade some roads to motorway status. In the Republic of Ireland, the National Roads Authority has been connecting main cities with motorways as part of a six-year National Development Plan. The European Union has part-funded many motorway projects in the past, as part of a Trans-European Transport Networks, and there are plans to invest billions of euro in such projects in the next ten years.
The newest UK motorway is the M6 Toll bypassing Birmingham and Wolverhampton, which opened in 2004 and is the only completely toll motorway in England. There are two other tolled sections of motorway (on the M4 and M48), but only where these motorways cross the Severn Bridges.
In the UK, certain types of traffic are not permitted on motorways. Thus, to avoid people being forced to travel illegally, there are a number of rules about stretches of road which must be designated as motorways.
In all cases, there must be an escape route for traffic not wishing or not permitted to enter the motorway. As a result, the motorway technically begins as soon as the escape route has diverged from it; e.g. at a grade-separated junction, the motorway starts at the junction with the exiting slip road, and the opposite slip road is also part of the motorway for this and the following reason.
As a result, this creates a less-restrictive set of rules for the standard of the road. Roads whose only destination is a motorway must be assigned motorway status, notwithstanding the possibility of them not being built to normal motoway standards. For example, the A48(M) motorway outside Cardiff begins after the last exit to St Mellons, since by staying on the dual carriageway you cannot get anywhere other than the M4 eastbound; however, the A48(M) is a motorway-grade highway. On the other hand, there are roads such as the A6144(M) , a 1.2-mile long single-carriageway road, which are classified as such since they lead inescapably to the motorway (in this case, the M60).
- List of motorways in the United Kingdom
- Roads in Ireland
- Freeway (includes links to motorways around the world)
- UK topics
- Department of Transport (United Kingdom)
- National Roads Authority (Republic of Ireland)
- European Union Transport Policy
- CBRD Motorway Database
- UK Roads Portal
- Pathetic Motorways
- New concept in motorway design
- Example of unclassified route "inheriting" motorway status
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