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Motorway mark in Europe
Motorway mark in Europe

A motorway (in the United Kingdom, Ireland, New Zealand and some Commonwealth nations) is both a type of road and a classification. Motorways are 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.

Equivalent terms in other countries include autoroute, Autobahn, freeway, autostrada, autopista, motorvej, motorväg and autoput.



A Sunday in April 2004 at 5 pm local time on Britain's busy M25
A Sunday in April 2004 at 5 pm local time on Britain's busy M25

For a road to be classified as motorway a number of conditions must be fulfilled. The following conditions generally apply:

  • Motorways must be accessed at junctions by slip roads off the sides of the main carriageway;
  • 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 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).

In the UK and the Republic of Ireland there are further restrictions:

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 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 (110 km/h) limit (the limit in Ireland and New Zealand is the regular 100 km/h (65 mph) limit). They may be subject to a lower speed limit (e.g. in urban areas).

Queues after an accident on Britain's M4
Queues after an accident on Britain's M4

In Ireland and the UK, motorways are denoted by blue signage and an M-prefixed or suffixed road number. Speed limits are generally higher than on ordinary roads, with an overall limit of 70 mph (110 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. Some vehicles, notably heavy goods vehicles, are not permitted to use the rightmost lane on a three (or more) lane motorway.

Roads in the Republic of Ireland have had metric speed limits since 20 January 2005 to conform 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).

In New Zealand motorways were historically distinguished from other roads with green signage. This changed with the establishment of Transit New Zealand which extended the use of green signs to the entire state highway network. The speed limit on motorways is fixed at the top limit for state highways, 100 km/h (65 mph). This rule is most in evidence in Wellington where Centennial Highway in the Ngauranga Gorge is not designated as a motorway because of the steep gradient, general usage and slow-speed junctions, despite leading directly into the Johnsonville-Porirua motorway.

The Conservative Party had proposed increasing the UK motorway speed limit to 80 mph (130 km/h), should they gained power at the past 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 further from the median) unless traffic in the 'faster' lanes is stationary. With a touch of black humour, the practice is popularly known as undertaking.


Diagram showing lanes and road layout, with Irish road markings.
Diagram showing lanes and road layout, with Irish road markings.

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 maneuvers. 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), as in the UK it is illegal to overtake on the left (commonly known as undertaking) except in emergencies, when signs indicate drivers may do so, or when traffic is moving slowly.

Traffic should always use the lefthandmost lane possible. Generally this means a vehicle should use the lefthand lane next to the hard shoulder, and use the other two lanes only for overtaking manouvers, moving back into the left lane once they have passed the slower vehicle(s). In heavy traffic, it is acceptable to cruise in the middle lane to pass slower vehicles to avoid constant lane changes.

A significant problem on motorways is the 'middle lane hog', a driver who drives in the middle lane when there is no reason to do so. This can be very frustrating for other drivers. Faster vehicles approaching in the left hand lane have to manouver across four lanes of the motorway rather than two to pass such a vehicle, since undertaking is forbidden. Drivers of heavy goods vehicles can be especially frustrated by a middle lane hog, as their vehicles are not permitted to use the righthandmost lane under normal circumstances. Since undertaking is forbidden, a heavy goods vehicle cannot legally pass a slower moving vehicle in the centre lane.

In the UK lanes in a given direction are numbered from left to right as lane 1, lane 2, lane 3, etc. Lane 1 is the lane next to the hard shoulder.

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.

Toll charges for Britain's M6 Toll
Toll charges for Britain's M6 Toll

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 tolled sections of motorway on the M4 and M48, where they cross the the River Severn at the Severn crossings.


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; for example 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 motorway 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 mi (2 km) long single-carriageway road, which are classified as such since they lead inescapably to the motorway (in this case, the M60).

Route numbering

In the United Kingdom, motorways sometimes adopt the number of the nearest "A" road heading in broadly the same direction. However this is just for convenience, and about half of motorways don't bypass the A road with the same number - Motorways follow their own zonal pattern, similar to the A+B road zones, but with the boundarys formed by the 1-digit motorways (and various A roads where there are gaps), as opposed to the one-digit A roads (NB, the 4 zone seems to be hourglass shaped and motorways west of the M5 but south of the M4 have 4-zone numbers). The A road usually continues to also use that number, thus allowing both an "A1" road and "M1" motorway to exist as full complementary routes.

In the Republic of Ireland, motorway and national route numbering does not follow the same convention. As of 2005, all motorways in the Republic are part of, or form, National Primary Routes. These routes are numbered in series, using numbers from 1 to 33 (and separately from the series - 50), which apart from on motorways, carry an "N" prefix.

In the Republic of Ireland, motorways use this route number (of the national route they form part of) with an M prefix rather than N. In most cases, the motorway has been built as a bypass of a road previously forming the national route (e.g. M7 bypassing roads previously forming the N7) - the bypassed roads are reclassified as Regional Roads, although updated signposting may not be provided for some time, and adherence to signage colour conventions is lax (regional roads have black-on-white directional signage, national routes use white-on-green).

The M50, an entirely new national route, is an exception to the normal inheritance process - as it does not replace a road previously carrying an "N" number. The M50 was nevertheless legislated as the "N50" route (despite having no non-motorway sections). The M50's designation was chosen as a recognisable unique number (As of 2005 N34 is the next unused National Primary Route designation).

See also

External links

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