The M4, originally the London-South Wales Motorway, is a

motorway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms ...

in the United Kingdom running from west London to southwest

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. The English section to the Severn Bridge was constructed between 1961 and 1971; the Welsh element was largely complete by 1980, though a non-motorway section around

Briton Ferry Briton Ferry ( cy, Llansawel) is a town and community in the county borough of Neath Port Talbot, Wales. The Welsh name may indicate that the church, ''llan'', is protected from the wind, ''awel''. Alternatively, ''Sawel'' may be a derivati ...

bridge remained until 1993. On the opening of the Second Severn Crossing in 1996, the M4 was rerouted over it. The line of the motorway from London to Bristol runs closely in parallel with the A4. After crossing the

River Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...

, toll-free since 17 December 2018, the motorway follows the A48, to terminate at the

Pont Abraham services Pont, meaning "bridge" in French, may refer to: Places France * Pont, Côte-d'Or, in the Côte-d'Or ''département'' * Pont-Bellanger, in the Calvados ''département'' * Pont-d'Ouilly, in the Calvados ''département'' * Pont-Farcy, in the Calv ...

Carmarthenshire Carmarthenshire ( cy, Sir Gaerfyrddin; or informally ') is a county in the south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. The county is known as ...

. The M4 is the only motorway in Wales apart from its two spurs: the A48(M) and the M48. The major towns and cities along the routea distance of approximately include

Slough Slough () is a town and unparished area in the unitary authority of the same name in Berkshire, England, bordering west London. It lies in the Thames Valley, west of central London and north-east of Reading, at the intersection of the ...

Reading Reading is the process of taking in the sense or meaning of letters, symbols, etc., especially by sight or touch. For educators and researchers, reading is a multifaceted process involving such areas as word recognition, orthography (spell ...

Swindon Swindon () is a town and unitary authority with borough status in Wiltshire, England. As of the 2021 Census, the population of Swindon was 201,669, making it the largest town in the county. The Swindon unitary authority area had a population ...

Bristol Bristol () is a City status in the United Kingdom, city, Ceremonial counties of England, ceremonial county and unitary authority in England. Situated on the River Avon, Bristol, River Avon, it is bordered by the ceremonial counties of Glouces ...

, Newport,

Cardiff Cardiff (; cy, Caerdydd ) is the capital city, capital and List of urban areas in the United Kingdom, largest city of Wales. It forms a Principal areas of Wales, principal area, officially known as the City and County of Cardiff ( cy, Dinas a ...

Bridgend Bridgend (; cy, Pen-y-bont ar Ogwr or just , meaning "the end of the bridge on the Ogmore") is a town in Bridgend County Borough in Wales, west of Cardiff and east of Swansea. The town is named after the medieval bridge over the River Og ...

Port Talbot Port Talbot (, ) is a town and community in the county borough of Neath Port Talbot, Wales, situated on the east side of Swansea Bay, approximately from Swansea. The Port Talbot Steelworks covers a large area of land which dominates the south ...

and

Swansea Swansea (; cy, Abertawe ) is a coastal city and the second-largest city of Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the C ...

History

A new road from London to South Wales was first proposed in the 1930s. In 1956 the

Ministry of Transport A ministry of transport or transportation is a ministry responsible for transportation within a country. It usually is administered by the ''minister for transport''. The term is also sometimes applied to the departments or other government ...

announced the plans for the first major post-war road improvement projects. The

Chiswick flyover The Chiswick flyover is a short elevated section of the M4 motorway in the western approaches to London, United Kingdom. The flyover in the west London suburb of Chiswick, was opened in 1959 with the intention of reducing congestion and the im ...

, a short section of elevated dual-carriageway, not originally classed as a motorway, opened in 1959 to reduce the impact of traffic travelling between central London and the west. M4 River Neath Crossing

The

Maidenhead Maidenhead is a market town in the Royal Borough of Windsor and Maidenhead in the county of Berkshire, England, on the southwestern bank of the River Thames. It had an estimated population of 70,374 and forms part of the border with southern Bu ...

bypass (J7-J9) opened in 1961, the section from Slough to Maidenhead (J5-J7) opened in 1963 and J1-J5 opened on 24 March 1965 incorporating the Chiswick Flyover. The stretch from J18 to the west of Newport was opened in 1966, including the Severn Bridge. The

by-pass, also built in the 1960s and now part of the M4, was originally the A48(M) motorway, a number now allocated to a short section of motorway near Cardiff. The Ministry of Transport originally intended that the M4 would terminate at

Tredegar Park Tredegar Park ( cy, Parc Tredegar) is a public park situated in the western Coedkernew area of the city of Newport, South Wales. It lies close to junction 28 of the M4 motorway connecting London and West Wales. History It formerly forme ...

west of Newport, and following the creation of the

Welsh Office The Welsh Office ( cy, Swyddfa Gymreig) was a department in the Government of the United Kingdom with responsibilities for Wales. It was established in April 1965 to execute government policy in Wales, and was headed by the Secretary of State f ...

that the Government became committed to a high-standard dual carriageway to

. The English section of the motorway was completed on 22 December 1971 when the stretch between junctions 9 and 15 (

and

) was opened to traffic. The Welsh section was largely completed between 1970 and 1980, though a non-motorway section remained across the

bridge until 1993, when a second motorway-only bridge opened. In 1996, the Second Severn Crossing opened with new link motorways on either side of the estuary to divert the M4 over the new crossing. At the same time, the original route over the Severn Bridge was redesignated the M48, and the M49 was opened to link the new crossing with the M5 at

Avonmouth Avonmouth is a port and outer suburb of Bristol, England, facing two rivers: the reinforced north bank of the final stage of the Avon which rises at sources in Wiltshire, Gloucestershire and Somerset; and the eastern shore of the Severn Es ...

. The new M49 shortened the route between South Wales and the South West, and reduced traffic at the busy M4/M5 junction at Almondsbury.

After completion

In April 2005, speed checks carried out by police camera vans between junction 14 and junction 18 led to a public protest, involving a "go-slow" of several hundred vehicles along the affected sections of the motorway. Between 2007 and January 2010, the section from Castleton (junction 29) to Coryton (junction 32) was widened to six lanes. The scheme was formally opened on 25 January 2010 by

Ieuan Wyn Jones Ieuan Wyn Jones (born 22 May 1949) is a Welsh politician who was the Deputy First Minister in the Welsh Government from 2007 to 2011. He was the Member of the Senedd for the Ynys Môn constituency from 1999 to 2013, and he was also leader of P ...

the Deputy First Minister for Wales. During 2009, the Newport section of the motorway between junctions 23a and 29 was upgraded with a new concrete central barrier. In February 2010 it was proposed that the M4 in South Wales would become the first

hydrogen highway A hydrogen highway is a chain of hydrogen-equipped public filling stations, along a road or highway, that allows hydrogen powered cars to travel. It is an element of the hydrogen infrastructure that is generally assumed to be a pre-requisite for m ...

with

hydrogen station A hydrogen station is a storage or filling station for Hydrogen. The hydrogen is dispensed by weight. There are two filling pressures in common use. H70 or 700 bar, and the older standard H35 or 350 bar. As of 2021 around 550 filling stations were ...

s provided along the route, with an aspiration for further stations to be provided along the M4 into

South West England South West England, or the South West of England, is one of nine official regions of England. It consists of the counties of Bristol, Cornwall (including the Isles of Scilly), Dorset, Devon, Gloucestershire, Somerset and Wiltshire. Cities ...

over time. Between 2008 and 2010, junction 11 was extensively remodelled with a new four-lane junction, two new road bridges and other works. The £65m scheme included work on the Mereoak roundabout and part of the A33 Swallowfield Bypass near

Shinfield Shinfield is a village and civil parish in the English county of Berkshire, just south of Reading. It contains and is administered by the unitary authority of Wokingham District. Shinfield Park is the northern part of the parish, becoming ph ...

, and also the conversion of the two existing bridges, one of which is available only to pedestrians and cyclists and the other to buses. It also involved the movement of the local

Highways Agency National Highways, formerly the Highways Agency and later Highways England, is a State-owned enterprise, government-owned company charged with operating, maintaining and improving Roads in England, motorways and major A roads in England. It al ...

and

Fire Service A fire department (American English) or fire brigade (Commonwealth English), also known as a fire authority, fire district, fire and rescue, or fire service in some areas, is an organization that provides fire prevention and fire suppression se ...

offices, and the construction of a long footbridge network, a new

bus lane A bus lane or bus-only lane is a lane restricted to buses, often on certain days and times, and generally used to speed up public transport that would be otherwise held up by traffic congestion. The related term busway describes a roadwa ...

and a new

gyratory A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford Eng ...

. Sound barriers for nearby residential areas were also installed. In April 2008, the decision to preserve a rare

Vickers machine gun The Vickers machine gun or Vickers gun is a water-cooled .303 British (7.7 mm) machine gun produced by Vickers Limited, originally for the British Army. The gun was operated by a three-man crew but typically required more men to move and o ...

pillbox Pillbox may refer to: * Pill organizer, a container for medicine * Pillbox hat, a woman's hat with a flat crown, straight upright sides, and no brim * Pillbox (military) A pillbox is a type of blockhouse, or concrete dug-in guard-post, norm ...

and turn it into a

bat roost Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

was announced by the developers.

Former bridge tolls

Tolls were charged on the Severn Bridge(s) from opening until 2018. In 1966 the toll was 12.5p each-way for cars, rising to 1 pound in the late 1980s. Around 1991 the toll was doubled but charged in the westbound direction only, to reduce queuing. After 1996 the tolls were equal westbound-only on both bridges, and rose steeply after 2000 to a peak of 6.70 for cars in 2017, leading to protests from Welsh businesses. Tolls on both bridges over the

River Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...

were eliminated on 17 December 2018, and the former toll booths were removed in 2019.

Timeline of construction

Maintenance

Maintenance of the Second Severn Crossing and the of motorway in England is the responsibility of

National Highways National Highways, formerly the Highways Agency and later Highways England, is a government-owned company charged with operating, maintaining and improving motorways and major A roads in England. It also sets highways standards used by all f ...

. The in Wales is the responsibility of the

South Wales Trunk Road Agent The South Wales Trunk Road Agent (SWTRA; cy, Asiant Cefnffyrdd De Cymru) is one of the two trunk road agents in Wales. It is responsible for managing motorways and trunk roads in South Wales on behalf of the Welsh Government. Established on 1 A ...

Features

Speed limits

For the majority of its length, the national speed limit applies. Exceptions include the following: * on the Chiswick Flyover within London in both directions. * between junction 4 and the Chiswick Flyover, eastbound only. * on the Port Talbot elevated section between junction 40 and junction 41. The fixed speed camera was removed in 2006 as it was believed to be causing tailbacks. In July 2014, an average speed camera system was installed; it generated around £500,000 in fines in the first six months. * between junctions 24 and 28 at Newport.

Smart motorway

The M4 has one section of smart motorway, between junctions 19 (M32) and 20 (M5) north of Bristol, where there are variable speed limits and a part-time hard-shoulder. Completion was in summer 2014. Another section between junctions 24 and 29 in Newport had variable speed limits until 2021, when it was changed to a permanent 50 mph limit with average speed cameras. In 2010, it was announced that the motorway would be changed to a smart motorway between junctions 3 and 12. With a length of , this will be the longest smart motorway scheme in the United Kingdom. Work started in autumn 2018 and is expected to be completed in March 2022 at a cost of £848 million.

Brynglas tunnels

The

Brynglas Tunnels The Brynglas Tunnels carry the M4 under Brynglas Hill in Newport, Wales. The tunnels are the first and only twin–bored tunnels in the UK motorway network. The tunnels and adjacent M4 motorway Usk bridge were originally planned by Newport ...

carry the M4 under

Brynglas Brynglas is an area of the city of Newport, South Wales, United Kingdom. Location Brynglas is situated above the M4 motorway in Newport and famous on traffic reports of congestion at the Brynglas Tunnels. Amenities & history Brynglas ...

Hill in

Newport, Wales Newport ( cy, Casnewydd; ) is a city and county borough in Wales, situated on the River Usk close to its confluence with the Severn Estuary, northeast of Cardiff. With a population of 145,700 at the 2011 census, Newport is the third-larges ...

. The tunnels are the first and only twin–bored tunnels in the UK motorway network (the Dartford Tunnel is not classified as part of the

M25 motorway The M25 or London Orbital Motorway is a major road encircling most of Greater London. The motorway is one of the most important roads in the UK and one of the busiest. Margaret Thatcher opened the final section in 1986, making the M25 the lon ...

). In July 2011, a lorry fire in one tunnel closed the motorway. Although there were no injuries and no deaths, the tunnel remained closed and a contraflow system was in place in the remaining tunnel for about one month, causing major travel delays.

Bus lane

In June 1999, the M4 bus lane was created on the third lane between junctions 2 and 3, initially as a pilot scheme and then a permanent arrangement from 2001. A lower speed limit was introduced along this section at the same time. The bus lane was on the eastbound carriageway; from the western end of the Chiswick Flyover near

Brentford Brentford is a suburban town in West London, England and part of the London Borough of Hounslow. It lies at the confluence of the River Brent and the Thames, west of Charing Cross. Its economy has diverse company headquarters buildings wh ...

to junction 3 (A312), covering part of the journey between

Heathrow Airport Heathrow Airport (), called ''London Airport'' until 1966 and now known as London Heathrow , is a major international airport in London, England. It is the largest of the six international airports in the London airport system (the others be ...

and central London. The lane which had no intermediate exits was for use by buses, coaches, motorcycles, emergency vehicles and licensed taxis but not mini-cabs. In December 2010, the bus lane was suspended for 18 months. It was reinstated temporarily for the

2012 Summer Olympics The 2012 Summer Olympics (officially the Games of the XXX Olympiad and also known as London 2012) was an international multi-sport event held from 27 July to 12 August 2012 in London, England, United Kingdom. The first event, th ...

and then permanently decommissioned.

Porous road surface

Near Junction 35 of the M4, there is a stretch of the motorway that has a surfacing of porous

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

that improves drainage and reduces noise. When driving in heavy rain drivers notice a reduction in

road spray Road debris, a form of road hazard, is debris on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment. Debris may be produced by vehicular or non-vehicular sources, but in all ...

from other vehicles and improved visibility. This special surface was publicised in an episode of the BBC's ''

Tomorrow's World ''Tomorrow's World'' is a former British television series about contemporary developments in science and technology. First transmitted on 7 July 1965 on BBC1, it ran for 38 years until it was cancelled at the beginning of 2003. The ''Tomorro ...

'' programme. This was the site of the first trial of the new road surface when it was laid down in 1993.

Elevated and heated section

The elevated section of the M4 in West London, built in the 1960s, is mostly directly above the A4 and extends over parts of

's Golden Mile. This section was designed to have a heated road surface to reduce icing in winter.

Four level stack interchanges

The M4 has two of the three four-level

stack interchange A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges e ...

s in the UK, including the first UK example at junction 20, the " Almondsbury Interchange" with the M5. The other is junction 4b with the M25. Junction 4b has to make provision for the railway line passing beneath the M4. Due to the nature of these junctions, one cannot make a U-turn at either of them.

Notable junctions

Junction 8/9 near

Berkshire Berkshire ( ; in the 17th century sometimes spelt phonetically as Barkeshire; abbreviated Berks.) is a historic county in South East England. One of the home counties, Berkshire was recognised by Queen Elizabeth II as the Royal County of Ber ...

, and

High Wycombe High Wycombe, often referred to as Wycombe ( ), is a market town in Buckinghamshire, England. Lying in the valley of the River Wye, Buckinghamshire, River Wye surrounded by the Chiltern Hills, it is west-northwest of Charing Cross in London, ...

Buckinghamshire Buckinghamshire (), abbreviated Bucks, is a ceremonial county in South East England that borders Greater London to the south-east, Berkshire to the south, Oxfordshire to the west, Northamptonshire to the north, Bedfordshire to the north-e ...

is the only one in the UK with dual numbers. This arose at the time when the M4 turned north near junction 8, where it met the A308, and headed for the original junction 9, where the motorway ended at a

roundabout A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford Eng ...

interchange with the A4. When the westward extension was opened, junction 8 was closed and a new junction built a little to the west, taking both numbers. The road to the A4 became A423(M) and later A404(M), and the junction with the A4 became 9B. Junction 9A is the exit for Cox Green and

White Waltham White Waltham is a village and civil parish, west of Maidenhead, in the Royal Borough of Windsor and Maidenhead in Berkshire, England. It is crossed briefly by the M4 motorway, which along with the Great Western Main Line and all other roads c ...

. To the west of junction 13 on the eastbound carriageway there are a set of sliproads signposted "Works Unit Only". The signs have red borders, implying a military exit. It is a back entrance to

RAF Welford Royal Air Force Welford or more simply RAF Welford is an active Royal Air Force station in Berkshire, England. The station is located approximately northwest of Newbury; about west-southwest of London Opened in 1943, it was used during the Se ...

, a Second World War airfield and now an RAF/

USAF The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...

military installation mainly used for storing munitions. The M4 entrance allows easier access for the large vehicles used to carry the munitions. Plans for the "missing" Junction 31, also known as the Thornhill interchange, for which

planning permission Planning permission or developmental approval refers to the approval needed for construction or expansion (including significant renovation), and sometimes for demolition, in some jurisdictions. It is usually given in the form of a building per ...

was originally granted in September 1991 (but subsequently expired), were rekindled after proposals for a new business park on a site north of the M4 were submitted in 2007 to

Cardiff Council Cardiff Council, formally the County Council of the City and County of Cardiff ( cy, Cyngor Sir Dinas a Sir Caerdydd) is the governing body for Cardiff, one of the Principal Areas of Wales. The principal area and its council were establishe ...

. The developers of the business park, St Modwen Developments, would likely fund the new junction, which would be on the A469. A freedom of information request in 2010 to Cardiff Council shows that whilst the land that would enable this junction should continue to be strategically protected, the decision to formally abandon the proposed Junction 31 Thornhill was made in October 2007 and there had been no subsequent mention of it in Cardiff Council Strategic or Planning meetings since. In South Wales, the M4 has to thread its way through mountainous terrain and built-up areas, so there are some unusual junction layouts. Junction 27 (

High Cross A high cross or standing cross ( ga, cros ard / ardchros, gd, crois àrd / àrd-chrois, cy, croes uchel / croes eglwysig) is a free-standing Christian cross made of stone and often richly decorated. There was a unique Early Medieval tradit ...

) is a normal grade-separated roundabout junction, but has severe space constraints: traffic joining the motorway must initially travel in the opposite direction to the intended direction of travel, before making a sharp left-hand turn from the slip road onto the motorway. At the time of construction, junction numbers 30 and 31 were reserved for future intermediate interchanges. Junction 30 (

Cardiff Gate Cardiff Gate is a business park development, located on the junction 30 of the M4 motorway and the A4232 north east of Cardiff, South Wales. Development In light of the development of farmland into housing at Pontprennau in the east of Cardiff i ...

) has since been added, but there are no current plans to construct Junction 31 (

A469 road The A469 is a road in south Wales. It links Cardiff and Caerphilly with Rhymney and the Heads of the Valleys Road (A465). See also * Transport in Cardiff * Transport in Wales Transport in Wales is heavily influenced by the countr ...

). Junction 39 can only be used to access the motorway from a single slip road onto the westbound carriageway from the A48 at junction 38. There is no exit from the motorway at this junction. Junction 41 comprises two different junctions; one for local traffic to and from the west and one from the east. The former leads to and from a spur leading to the roundabout in

, formerly known as junction 41a, and the original bridge over the

River Neath River Neath ( cy, Afon Nedd) is a river in south Wales running south west from the point at which its headwaters arising in the Brecon Beacons National Park converge to its mouth at Baglan Bay below Briton Ferry on the east side of Swansea Bay. ...

, which would allow access onto the stretch of the M4 from junction 43 westward. The second, eastern junction leads to and from the A48 towards

. As a result, one can travel for almost on the motorway in either direction, both joining and then leaving the motorway at junction 41. Junction 44 is unusual in that the eastbound entrance dives under the inside of the junction, effectively creating a "right-turn" on a roundabout. Similarly, slip roads pass under or over the main motorway at junctions 41 and 42. There have been calls to close the

slip road In the field of road transport, an interchange (American English) or a grade-separated junction (British English) is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, usin ...

s at junctions 40 and 41 to improve traffic flow. The motorway has only two lanes on this stretch and is a major traffic congestion blackspot. The short slip roads have not been modernised. A small-scale trial of closing the westbound on-slip of junction 41 between 7 am and 9 am and from 4 pm to 6 pm on weekdays started on 4 August 2014 but following heavy criticism from local businesses and residents, was stopped on 29 May 2015.

Relief road

On 5 June 2019, the

Welsh Government The Welsh Government ( cy, Llywodraeth Cymru) is the Welsh devolution, devolved government of Wales. The government consists of ministers and Minister (government), deputy ministers, and also of a Counsel General for Wales, counsel general. Minist ...

scrapped the proposal for a proposed motorway south of Newport. The

Welsh Assembly Government Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peopl ...

had revived the scheme as a tolled bypass in 2007 and later abandoned it for financial reasons. An extension to the Newport

Southern Distributor Road The Southern Distributor Road (SDR) is a principal distributor road in Newport that runs from the Coldra roundabout ( M4 junction 24) in the east of Newport to Tredegar Park M4 Junction 28) in the west of Newport and includes City Bridge, a ...

through the old Corus steel works was considered. This road is already a dual carriageway. A public consultation exercise on options for improving the capacity of the

M4 corridor The M4 corridor is an area in the United Kingdom adjacent to the M4 motorway, which runs from London to South Wales. It is a major high-technology hub. Important cities and towns linked by the M4 include (from east to west) London, Slough, Brackne ...

around Newport opened on 5 March 2012. Its website states that: "the motorway around Newport does not conform to today’s motorway standards. It lacks continuous hard shoulders, has closely spaced junctions with sub-standard slip road visibility and narrows to a restricted two lane section through the Brynglas Tunnels. Heavy congestion occurs along this stretch and either side of it at peak hours."

List of junctions

{, style="margin-left:1em; margin-bottom:1em; color:black; font-size:90%;" class="wikitable" , - style="background:#0080d0; text-align:center; color:white; font-size:120%;" , colspan="5" , M4 motorway , - !scope=col, mile !scope=col, km !scope=col abbr="Eastbound", Eastbound exits (B carriageway) !scope=col, Junction !scope=col abbr="Westbound", Westbound exits (A carriageway) , - style="text-align:center;" , 7.3 , 11.8 , ''Road continues as A4 to

Central London Central London is the innermost part of London, in England, spanning several boroughs. Over time, a number of definitions have been used to define the scope of Central London for statistics, urban planning and local government. Its characteris ...

'' , J1
Eastern end of M4 , ''Start of motorway'' , - style="text-align:center;" , 8.3
8.5 , 13.4
13.7 ,

North Circular The North Circular Road (officially the A406 and sometimes known as simply the North Circular) is a ring road around Central London in England. It runs from Chiswick in the west to Woolwich in the east via suburban North London, connecting ...

A406 The North Circular Road (officially the A406 and sometimes known as simply the North Circular) is a ring road around Central London in England. It runs from Chiswick in the west to Woolwich in the east via suburban North London, connecting ...

South Circular A205

Chiswick Chiswick ( ) is a district of west London, England. It contains Hogarth's House, the former residence of the 18th-century English artist William Hogarth; Chiswick House, a neo-Palladian villa regarded as one of the finest in England; and F ...

A315 , J2 , Staines,

Hounslow Hounslow () is a large suburban district of West London, west-southwest of Charing Cross. It is the administrative centre of the London Borough of Hounslow, and is identified in the London Plan as one of the 12 metropolitan centres in ...

A4 , - style="text-align:center;" , 12.5
12.8 , 20.1
20.6 , ''

Heston services Heston services is a motorway service station on the M4 motorway in the London Borough of Hounslow, built on land that once formed part of the now defunct Heston Aerodrome. History It is owned by Moto. The 11-mile £19m Chiswick-Langley sect ...

'' , ''Services'' , ''Heston services'' , - style="text-align:center;" , 13.4
13.7 , 21.5
22.1 ,

Heathrow Heathrow Airport (), called ''London Airport'' until 1966 and now known as London Heathrow , is a major international airport in London, England. It is the largest of the six international airports in the London airport system (the others bei ...

(Terminals 4, 5 & Cargo),

Hayes Hayes may refer to: * Hayes (surname), including a list of people with the name ** Rutherford B. Hayes, 19th president of the United States * Hayes (given name) Businesses * Hayes Brake, an American designer and manufacturer of disc brakes * Hay ...

, Harrow,

A312 , J3 ,

(Terminals 4, 5 & Cargo), Hayes, Harrow, Hounslow A312 , - style="text-align:center;" , 15.2
15.7 , 24.5
25.2 , Heathrow 20 airtransportation

(Terminals 2 & 3) (A4)
Uxbridge A408 , J4a ,

(Terminals 2 & 3) (A4)

Uxbridge Uxbridge () is a suburban town in west London and the administrative headquarters of the London Borough of Hillingdon. Situated west-northwest of Charing Cross, it is one of the major metropolitan centres identified in the London Plan. Uxb ...

A408 , - style="text-align:center;" , 16.8
17.7 , 27.0
28.5 ,

(Terminals 4, 5 & Cargo) 20 airtransportation

Gatwick Airport Gatwick Airport (), also known as London Gatwick , is a major international airport near Crawley, West Sussex, England, south of Central London. In 2021, Gatwick was the third-busiest airport by total passenger traffic in the UK, after ...

Watford Watford () is a town and borough in Hertfordshire, England, 15 miles northwest of Central London, on the River Colne. Initially a small market town, the Grand Junction Canal encouraged the construction of paper-making mills, print works, and ...

(M3), (M23), (M40), (M1) M25 , J4b
''Harmondsworth Interchange'' Intersection of M25 and M4 , Heathrow (Terminals 4, 5&Cargo), Gatwick, Watford (M3), (M23), (M40), (M1), M25 , - style="text-align:center;" , , , style=background:skyblue , ''Entering

Greater London Greater may refer to: *Greatness Greatness is a concept of a state of superiority affecting a person or object in a particular place or area. Greatness can also be attributed to individuals who possess a natural ability to be better than al ...

'' , , style=background:skyblue , ''Entering

'' , - style="text-align:center;" , 19.1
19.5 , 30.7
31.4 ,

Colnbrook Colnbrook is a village in the Slough district in Berkshire, England. It lies within the historic boundaries of Buckinghamshire, and straddles two distributaries of the Colne, the Colne Brook and Wraysbury River. These two streams have their co ...

, Langley, Slough (East) A4
Eton,

Datchet Datchet is a village and civil parish in the Royal Borough of Windsor and Maidenhead in Berkshire, England, located on the north bank of the River Thames. Historically part of Buckinghamshire, and the Stoke Hundred, the village was eventual ...

B470 , J5 ,

, Langley, Slough (East) A4,

B470 , - style="text-align:center;" , 22.9
23.2 , 36.8
37.4 , Slough (Central) A355

Windsor Windsor may refer to: Places Australia * Windsor, New South Wales ** Municipality of Windsor, a former local government area * Windsor, Queensland, a suburb of Brisbane, Queensland **Shire of Windsor, a former local government authority around Wi ...

A322 , J6 , Slough (Central) A355

A322 , - style="text-align:center;" , , , style=background:skyblue , ''Entering

'' , , style=background:skyblue , ''Entering

'' , - style="text-align:center;" , 24.7
25.0 , 39.8
40.3 , Slough (West) A4 , J7 , Slough (West) A4 , - style="text-align:center;" , , , style=background:skyblue , ''Entering

'' , , style=background:skyblue , ''Entering

'' , - style="text-align:center;" , 27.8
28.2 , 44.7
45.4 ,

Henley Henley may refer to: Places United Kingdom * Henley, Dorset, a location * Henley, Gloucestershire, a location * Henley-on-Thames, a town in South Oxfordshire, England ** Henley (UK Parliament constituency) ** Henley Rural District, a former ru ...

A404(M)

A308(M) , J8/9 ,

A404(M)

A308(M) , - style="text-align:center;" , 35.0
35.8 , 56.4
57.6 , Reading (East),

Wokingham Wokingham is a market town in Berkshire, England, west of London, southeast of Reading, north of Camberley and west of Bracknell. History Wokingham means 'Wocca's people's home'. Wocca was apparently a Saxon chieftain who may ...

Bracknell Bracknell () is a large town and civil parish in Berkshire, England, the westernmost area within the Greater London Urban Area and the administrative centre of the Borough of Bracknell Forest. It lies to the east of Reading, south of Maiden ...

A329(M) , J10 , Reading (East),

A329(M) , - style="text-align:center;" , 40.6
41.2 , 65.4
66.3 ,

Basingstoke Basingstoke ( ) is the largest town in the county of Hampshire. It is situated in south-central England and lies across a valley at the source of the River Loddon, at the far western edge of The North Downs. It is located north-east of Southa ...

, Reading (Central & South) A33 , J11 ,

, Reading (Central & South) A33 , - style="text-align:center;" , 43.5
43.8 , 70.0
70.5 , ''

Reading services Reading services comprises a pair of adjacent motorway service areas on the M4 motorway to the south of the town of Reading in the English county of Berkshire. The two areas are on opposite sides of the motorway, with Reading West services serv ...

'' , ''Services'' , ''

'' , - style="text-align:center;" , 45.3
45.7 , 72.9
73.5 , Reading (West),

Theale Theale () is a large village and civil parish in West Berkshire, England, southwest of Reading and 10 miles (16 km) east of Thatcham. The compact parish is bounded to the south and south-east by the Kennet & Avon Canal (which here incorp ...

A4 , J12 , Reading (West),

A4 , - style="text-align:center;" , 56.9
57.2 , 91.5
92.1 , Newbury,

Oxford Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...

A34
''

Chieveley services Chieveley services is a UK motorway service station just off the M4 motorway at Chieveley near Newbury in Berkshire, England. It is owned by Moto. It is situated on the A34 between Oxford and Winchester just off Junction 13 of the M4 (so ...

( Moto)'' , J13
''Services''
Intersection of M4 and A34 (E05) , Newbury,

A34
''

( Moto) '' , - style="text-align:center;" , 64.4
64.8 , 103.7
104.3 ,

Hungerford Hungerford is a historic market town and civil parish in Berkshire, England, west of Newbury, east of Marlborough, northeast of Salisbury and 60 miles (97 km) west of London. The Kennet and Avon Canal passes through the town alongside the ...

Wantage Wantage () is a historic market town and civil parish in Oxfordshire, England. Although within the boundaries of the historic county of Berkshire, it has been administered as part of the Vale of White Horse district of Oxfordshire since 1974. T ...

A338 , J14 ,

A338 , - style="text-align:center;" , 68.7 , 110.5 , '' Membury services'' , ''Services'' , '' Membury services'' , - style="text-align:center;" , , , style=background:skyblue , ''Entering

'' , , style=background:skyblue , ''Entering

Wiltshire Wiltshire (; abbreviated Wilts) is a historic and ceremonial county in South West England with an area of . It is landlocked and borders the counties of Dorset to the southwest, Somerset to the west, Hampshire to the southeast, Gloucestershire ...

'' , - style="text-align:center;" , 76.4
77.1 , 122.9
124.0 ,

(East) A419
Marlborough A346

( A420) , J15 ,

A419, Marlborough A346 , - style="text-align:center;" , 82.4
82.8 , 132.6
133.2 ,

(West),

Royal Wootton Bassett Royal Wootton Bassett , formerly Wootton Bassett, is a market town and civil parish in Wiltshire, England, with a population of 11,043 in 2001, increasing to 11,385 in 2011. Situated in the north of the county, it lies to the west of the major ...

Wroughton Wroughton is a large village and civil parish in northeast Wiltshire, England. It is part of the Borough of Swindon and lies along the A4361 between Swindon and Avebury; the road into Swindon crosses the M4 motorway between junctions 15 ...

MoD Lyneham Ministry of Defence Lyneham or MOD Lyneham is a Ministry of Defence site in Wiltshire, England, about northeast of Chippenham and southwest of Swindon. The site houses the Defence School of Electronic and Mechanical Engineering. Also here is Pr ...

Calne Calne () is a town and civil parish in Wiltshire, southwestern England,OS Explorer Map 156, Chippenham and Bradford-on-Avon Scale: 1:25 000.Publisher: Ordnance Survey A2 edition (2007). at the northwestern extremity of the North Wessex Downs ...

A3102 , J16 , Swindon (West),

A3102 , - style="text-align:center;" , 94.8
95.3 , 152.5
153.4 ,

Chippenham Chippenham is a market town in northwest Wiltshire, England. It lies northeast of Bath, west of London, and is near the Cotswolds Area of Natural Beauty. The town was established on a crossing of the River Avon and some form of settlement i ...

A350 The Airbus A350 is a long-range, wide-body twin-engine jet airliner developed and produced by Airbus. The first A350 design proposed by Airbus in 2004, in response to the Boeing 787 Dreamliner, would have been a development of the A330 ...

Cirencester Cirencester (, ; see below for more variations) is a market town in Gloucestershire, England, west of London. Cirencester lies on the River Churn, a tributary of the River Thames, and is the largest town in the Cotswolds. It is the home of ...

A429 A4 most often refers to: *A4 paper, a paper size defined by the ISO 216 standard, measuring 210 × 297 mm A4 and variants may also refer to: Science and mathematics * British NVC community A4 (''Hydrocharis morsus-ranae - Stratiotes aloide ...

, J17 ,

, - style="text-align:center;" , 96.7 , 155.7 , ''

Leigh Delamere services Leigh Delamere services is a motorway service station on the M4 motorway situated one mile west of Junction 17, between Bristol and Swindon (close to Chippenham and Malmesbury). It takes its name from the adjoining village of Leigh Delamere. It ...

'' , ''Services'' , ''

'' , - style="text-align:center;" , , , style=background:skyblue , ''Entering

'' , , style=background:skyblue , ''Entering

Gloucestershire Gloucestershire ( abbreviated Glos) is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn and the entire Forest of Dean. The county town is the city of ...

'' , - style="text-align:center;" , 104.9
105.6 , 168.8
170.0 ,

Bath Bath may refer to: * Bathing, immersion in a fluid ** Bathtub, a large open container for water, in which a person may wash their body ** Public bathing, a public place where people bathe * Thermae, ancient Roman public bathing facilities Pl ...

Stroud Stroud is a market town and civil parish in Gloucestershire, England. It is the main town in Stroud District. The town's population was 13,500 in 2021. Below the western escarpment of the Cotswold Hills, at the meeting point of the Five Va ...

A46 , J18 ,

A46 , - style="text-align:center;" , 112.8
113.2 , 181.5
182.1 , Bristol M32 , J19 ,

M32 , - style="text-align:center;" , 115.8
116.3 , 186.3
187.2 , The South West,

(West),

The Midlands The Midlands (also referred to as Central England) are a part of England that broadly correspond to the Kingdom of Mercia of the Early Middle Ages, bordered by Wales, Northern England and Southern England. The Midlands were important in the In ...

Gloucester Gloucester ( ) is a cathedral city and the county town of Gloucestershire in the South West of England. Gloucester lies on the River Severn, between the Cotswolds to the east and the Forest of Dean to the west, east of Monmouth and east o ...

Bristol Airport Bristol Airport , at Lulsgate Bottom, on the northern slopes of the Mendip Hills, in North Somerset, is the commercial airport serving the city of Bristol, England, and the surrounding area. It is southwest of Bristol city centre. Built on ...

, M5 , J20
'' Almondsbury Interchange''
Almondsbury Interchange – Intersection of M4 and M5 , The South West, Bristol (West) M5(S)
The Midlands, Gloucester M5(N) , - style="text-align:center;" , 117.7
189.5 , 189.5
190.0 , No access , J21 ,

Chepstow Chepstow ( cy, Cas-gwent) is a town and community in Monmouthshire, Wales, adjoining the border with Gloucestershire, England. It is located on the tidal River Wye, about above its confluence with the River Severn, and adjoining the wester ...

M48 , - style="text-align:center;" , 121.3
121.6 , 195.2
195.7 ,

M49 , J22 , Avonmouth M49 , - style="text-align:center;" , rowspan=2 , 121.7
124.1 , rowspan=2 , 195.9
199.8 , style=background:skyblue , ''Entering

'' , rowspan=2 , '' Second Severn Crossing''
Second Severn Crossing , ''Entry into Wales'' , - style="text-align:center;" , ''Entry into England'' , style=background:skyblue , ''Entering Gwent'' , - style="text-align:center;" , 127.0 , 204.4 , ''No toll plaza'' , ''Bridge Toll'' , style="background:#dcdcfe;", ''Former toll plaza (closed Dec 2018)'' , - style="text-align:center;" , 129.2 , 208.0 ,

M48 , J23 , No access , - style="text-align:center;" , 131.4
132.2 , 211.4
212.8 , Magor, Caldicot A4810
''

Magor services Magor services (in Welsh: Gwasanaethau Magwyr) is a motorway service station on the M4, located just off junction 23A, at Magor near Newport, in Monmouthshire, South Wales. History The services opened in 1996 along with the Second Severn Cr ...

'' , J23A
''Services'' , Magor, Caldicot A4810
''

'' , - style="text-align:center;" , 134.8
135.6 , 217.0
218.3 ,

City centre A city centre is the commercial, cultural and often the historical, political, and geographic heart of a city. The term "city centre" is primarily used in British English, and closely equivalent terms exist in other languages, such as "" in Fren ...

A48
Newport (East) B4237

Monmouth Monmouth ( , ; cy, Trefynwy meaning "town on the Monnow") is a town and community in Wales. It is situated where the River Monnow joins the River Wye, from the Wales–England border. Monmouth is northeast of Cardiff, and west of London. ...

A449 The A449 is a major road in the United Kingdom. It runs north from junction 24 of the M4 motorway at Newport in South Wales to Stafford in Staffordshire. The southern section of the road, between Ross on Wye and Newport forms part of the tru ...

( M50) , J24 ,

A48
Newport (East) B4237

, - style="text-align:center;" , 137.9 , 222.0 , No access , J25 ,

Caerleon Caerleon (; cy, Caerllion) is a town and community in Newport, Wales. Situated on the River Usk, it lies northeast of Newport city centre, and southeast of Cwmbran. Caerleon is of archaeological importance, being the site of a notable Roman ...

B4596 , - style="text-align:center;" , 138.3 , 222.6 , No access , J25A , Newport,

Cwmbran Cwmbran ( ; cy, Cwmbrân , also in use as an alternative spelling in English) is a town in the county borough of Torfaen in South Wales. Lying within the historic boundaries of Monmouthshire, Cwmbran was designated as a New Town in 1949 to prov ...

A4042 , - style="text-align:center;" , 138.8
139.1 , 223.4
223.8 , ''

'' , ''Tunnel'' , ''

'' , - style="text-align:center;" , 139.1
139.5 , 223.8
224.5 , Newport,

A4051 , J26 , Newport A4051 , - style="text-align:center;" , 140.8
141,4 , 226.6
227.6 ,

B4591 , J27 ,

B4591 , - style="text-align:center;" , 142.0
142.9 , 228.5
230.0 , Newport A48

Risca Risca ( cy, Rhisga) is a town in the Caerphilly County Borough and the historic boundaries of Monmouthshire in south-east Wales. Risca has a railway station, opened on the Ebbw Valley Railway in February 2008, after a gap of 46 years. It is sp ...

Brynmawr Brynmawr (; , ,) is a market town, community and electoral ward in Blaenau Gwent, Wales. The town, sometimes cited as the highest town in Wales, is situated at above sea level at the head of the South Wales Valleys. It grew with the develo ...

A467 , J28 , Newport A48

A467 , - style="text-align:center;" , 143.6 , 231.1 , No access , J29 ,

(East and South) A48(M) , - style="text-align:center;" , , , style=background:skyblue , ''Entering Gwent'' , , style=background:skyblue , ''Entering

South Glamorgan , Government= South Glamorgan County Council , Status= Non-metropolitan county (1974–1996) Preserved county (1996–) , Start= 1974 , End= 1996 , Arms= , HQ= ...

'' , - style="text-align:center;" , 146.6
147.3 , 236.0
237.0 , Cardiff (East) A4232
''

Cardiff Gate services Cardiff Gate services ( cy, Gwasanaethau Porth Caerdydd) is the motorway service station on the junction of the M4 motorway (junction 30) and the A4232, located on the Cardiff Gate International Business Park, adjacent to Pontprennau, north e ...

'' , J30
''Services'' , Cardiff (East) A4232
''

'' , - style="text-align:center;" , 151.9
244.5 , 244.5
246.1 ,

Merthyr Tydfil Merthyr Tydfil (; cy, Merthyr Tudful ) is the main town in Merthyr Tydfil County Borough, Wales, administered by Merthyr Tydfil County Borough Council. It is about north of Cardiff. Often called just Merthyr, it is said to be named after T ...

A470 The A470 (also named the Cardiff to Glan Conwy Trunk Road) is a trunk road in Wales. It is the country's longest road at and links the capital Cardiff on the south coast to Llandudno on the north coast. While previously one had to navigat ...

, J32 , Cardiff (North),

, - style="text-align:center;" , 155.4
156.0 , 250.1
251.1 , Cardiff (West),

Barry Barry may refer to: People and fictional characters * Barry (name), including lists of people with the given name, nickname or surname, as well as fictional characters with the given name * Dancing Barry, stage name of Barry Richards (born c. 195 ...

Penarth Penarth (, ) is a town and Community (Wales), community in the Vale of Glamorgan ( cy, Bro Morgannwg), Wales, exactly south of Cardiff city centre on the west shore of the Severn Estuary at the southern end of Cardiff Bay. Penarth is a weal ...

A4232

Cardiff Airport Cardiff Airport ( cy, Maes Awyr Caerdydd) is the only airport offering commercial passenger services in Wales. It has been under the ownership of the Welsh Government since March 2013, operating at an arm's length as a commercial business. ...

Cardiff West services Cardiff West services ( cy, Gwasanaethau Gorllewin Caerdydd) is a motorway service station on junction 33 of the M4 motorway and the Capel Llanilltern junction of the A4232 near Cardiff, Wales. It is owned by Moto. In 2008, the services won th ...

'' , J33
''Services'' , Cardiff (West),

A4232

'' , - style="text-align:center;" , 157.5
158.1 , 253.5
254.4 ,

Llantrisant Llantrisant (; " Parish of the Three Saints") is a town in the county borough of Rhondda Cynon Taf, within the historic county boundaries of Glamorgan, Wales, lying on the River Ely and the Afon Clun. The three saints of the town's name are ...

Rhondda Rhondda , or the Rhondda Valley ( cy, Cwm Rhondda ), is a former coal mining, coalmining area in South Wales, historically in the county of Glamorgan. It takes its name from the River Rhondda, and embraces two valleys – the larger Rhondda Fa ...

A4119
Royal Glamorgan Hospital , J34 ,

A4119
Royal Glamorgan Hospital , - style="text-align:center;" , , , style=background:skyblue , ''Entering

South Glamorgan , Government= South Glamorgan County Council , Status= Non-metropolitan county (1974–1996) Preserved county (1996–) , Start= 1974 , End= 1996 , Arms= , HQ= ...

'' , , style=background:skyblue , ''Entering

Mid Glamorgan , Government= Mid Glamorgan County Council , Status= Non-metropolitan county (1974–1996) Preserved county (1996–) , Start= 1974 , End= 1996 , Arms= ''Coat of arms of Mid ...

'' , - style="text-align:center;" , 163.9
164.4 , 263.7
264.5 , Pen-coed A473 , J35 ,

, Pen-coed A473 , - style="text-align:center;" , 167.5
168.3 , 269.6
270.8 ,

A4061
Maesteg A4063

Princess of Wales Hospital The Princess of Wales Hospital ( cy, Ysbyty Tywysoges Cymru) is a district general hospital in Bridgend, Wales. It is managed by Cwm Taf Morgannwg University Health Board. History The hospital was commissioned to replace the aging Bridgend Gen ...

Sarn Park services Sarn Park services ( cy, Gwasanaethau Parc Sarn) is a motorway service station on the M4 motorway in Bridgend County Borough, Wales. It is situated at junction 36 of the motorway, north of the town of Bridgend, and is owned by Welcome Break. Brid ...

'' , J36
''Services'' ,

A4061
Maesteg A4063

'' , - style="text-align:center;" , 172.8
173.5 , 278.1
279.3 , Pyle,

Porthcawl Porthcawl (, ) is a town and community on the south coast of Wales in the county borough of Bridgend, west of the capital city, Cardiff and southeast of Swansea. Historically part of Glamorgan and situated on a low limestone headland on the S ...

A4229 , J37 ,

, Pyle A4229 , - style="text-align:center;" , , , style=background:skyblue , ''Entering

Mid Glamorgan , Government= Mid Glamorgan County Council , Status= Non-metropolitan county (1974–1996) Preserved county (1996–) , Start= 1974 , End= 1996 , Arms= ''Coat of arms of Mid ...

'' , , style=background:skyblue , ''Entering

West Glamorgan , HQ= County Hall, Swansea , Government= West Glamorgan County Council (abolished 1996) , Status= , Start= 1974 , End= 1996 , Arms= ''Coat of arms of Wes ...

'' , - style="text-align:center;" , 177.0
177.3 , 284.9
285.3 ,

A48 , J38 ,

A48 , - style="text-align:center;" , 178.3 , 286.9 , No access (on-ramp only) , J39 , No access , - style="text-align:center;" , 179.7
179.9 , 289.2
289.6 ,

A4107 , J40 ,

A4107 , - style="text-align:center;" , 180.9
181.3 , 291.1
291.8 ,

A48 , J41 ,

A48 , - style="text-align:center;" , 183.9
184.9 , 295.9
297.3 ,

A48
Swansea (South) A483 , J42 , Swansea (South) A483 , - style="text-align:center;" , 184.9
185.7 , 297.5
298.8 ,

Neath Neath (; cy, Castell-nedd) is a market town and community situated in the Neath Port Talbot County Borough, Wales. The town had a population of 50,658 in 2011. The community of the parish of Neath had a population of 19,258 in 2011. Historica ...

A465 The A465 is a trunk road that runs from Bromyard in Herefordshire, England to Llandarcy near Swansea in South Wales. The western half is known officially as the Neath to Abergavenny Trunk Road, but the section from Abergavenny to the Vale of N ...

, J43 ,

, - style="text-align:center;" , 187.0
187.4 , 300.9
301.6 , Swansea (East) A48 , J44 , Swansea (East) A48 , - style="text-align:center;" , 188.8
189.3 , 303.9
304.7 ,

Pontardawe Pontardawe () is a town and a community in the Swansea Valley (Welsh: ''Cwmtawe'') in Wales. With a population of 6,832, it comprises the electoral wards of Pontardawe and Trebanos. A town council is elected. Pontardawe forms part of the county ...

, Swansea (North)

A4067 List of A road A roads may be *motorways or freeways, usually where the local word for motorway begins with A (for example, ''Autobahn'' in German; ''Autostrada'' in Italian). * main roads or highways, in a system where roads are graded A, B ...

, J45 ,

, Swansea (North)

, - style="text-align:center;" , 190.8
191.4 , 307.0
308.0 ,

Llangyfelach Llangyfelach is a village and community located in the City and County of Swansea, Wales. Llangyfelach is situated about 4 miles north of the centre of Swansea, just west of Morriston. It falls within the Llangyfelach ward. To the west is open ...

B4489

Felindre Felindre is a rural village in southern Wales. Felindre is located in the far north of Swansea, in the electoral ward of Mawr. The nearby Lower Lliw Reservoirs are a popular venue for walking and fishing. The water mill in the village was workin ...

Morriston Hospital Morriston Hospital ( cy, Ysbyty Treforys) is a 750-bed hospital located in Cwmrhydyceirw near Morriston in Swansea, Wales. It is managed by Swansea Bay University Health Board. Alongside its role as a district general hospital, Morriston is a t ...

, J46 ,

B4489

, - style="text-align:center;" , 192.4
193.1 , 309.6
310.7 , Swansea (West) A483

Gorseinon Gorseinon is a town within the City and County of Swansea, Wales, near the Loughor estuary. It was a small village until the late 19th century when it grew around the coal mining and tinplate industries. It is situated in the north west of Sw ...

A48
''

Swansea services Swansea services ( cy, Gwasanaethau Gorllewin Abertawe, "Swansea West services") is a motorway service station on the M4 motorway at Junction 47 near Penllergaer, Swansea, Wales Wales ( cy, Cymru ) is a country that is part of the United K ...

'' , J47
''Services'' , Swansea (West) A483

A48
''

'' , - style="text-align:center;" , , , style=background:skyblue , ''Entering

West Glamorgan , HQ= County Hall, Swansea , Government= West Glamorgan County Council (abolished 1996) , Status= , Start= 1974 , End= 1996 , Arms= ''Coat of arms of Wes ...

'' , , style=background:skyblue , ''Entering

Dyfed Dyfed () is a preserved county in southwestern Wales. It is a mostly rural area with a coastline on the Irish Sea and the Bristol Channel. Between 1974 and 1996, Dyfed was also the name of the area's county council and the name remains in use f ...

'' , - style="text-align:center;" , 196.4
197.1 , 316.0
317.2 ,

Pontarddulais Pontarddulais (), also known as Pontardulais (), is both a community and a town in Swansea, Wales. It is northwest of the city centre. The Pontarddulais ward is part of the City and County of Swansea. Pontarddulais adjoins the village of Hend ...

Llanelli Llanelli ("St Elli's Parish"; ) is a market town and the largest community in Carmarthenshire and the preserved county of Dyfed, Wales. It is located on the Loughor estuary north-west of Swansea and south-east of the county town, Carma ...

A4138 , J48 ,

A4138 , - style="text-align:center;" , 199.2 , 320.6 , ''Start of motorway'' , J49
Terminus
''Services''
Western end of M4 , Motorway terminates at a roundabout:

Carmarthen Carmarthen (, RP: ; cy, Caerfyrddin , "Merlin's fort" or "Sea-town fort") is the county town of Carmarthenshire and a community in Wales, lying on the River Towy. north of its estuary in Carmarthen Bay. The population was 14,185 in 2011, ...

A48

Ammanford Ammanford ( cy, Rhydaman) is a town and community in Carmarthenshire, Wales, with a population of 5,411 at the 2011 census. It is a former coal mining town. The built-up area had a population of 7,945 with the wider urban area even bigger. Acc ...

Llandeilo Llandeilo () is a town and community in Carmarthenshire, Wales, situated at the crossing of the River Towy by the A483 on a 19th-century stone bridge. Its population was 1,795 at the 2011 Census. It is adjacent to the westernmost point of the ...

A483
Pontarddulais A48
''

'' , - ;Coordinate list Data from driver location signs and location marker posts are used to provide distance and carriageway identification information. Where a junction spans several hundred metres and the data is available, both the start and finish values for the junction are shown.

E30

Although not signed,

European route E30 European route E30 is an A-Class European route from the port of Cork in Ireland in the west to the Russian city of Omsk, near the border with Kazakhstan in the east. For much of the Russian stretch, it follows the Trans-Siberian Highway a ...

includes most of the M4. The entire route runs between

Cork Cork or CORK may refer to: Materials * Cork (material), an impermeable buoyant plant product ** Cork (plug), a cylindrical or conical object used to seal a container ***Wine cork Places Ireland * Cork (city) ** Metropolitan Cork, also known as G ...

in Ireland and

Omsk Omsk (; rus, Омск, p=omsk) is the administrative center and largest city of Omsk Oblast, Russia. It is situated in southwestern Siberia, and has a population of over 1.1 million. Omsk is the third largest city in Siberia after Novosibirsk a ...

in Russia.

Major incidents and accidents

* In June 1984 a crash near

resulted in 13 deaths. * In March 1991, ten people died in the

1991 M4 motorway crash __NOTOC__ On 13 March 1991, a multiple-vehicle collision occurred during foggy conditions on the eastbound carriageway of the M4 motorway near Hungerford, Berkshire, between the Membury service station and junction 14. Ten people were killed ...

near

. The crash involved 51 vehicles in foggy conditions. * In May 1995 a coach carrying

Royal British Legion The Royal British Legion (RBL), formerly the British Legion, is a British charity providing financial, social and emotional support to members and veterans of the British Armed Forces, their families and dependants, as well as all others in ...

members left the M4 close to the Severn Bridge, resulting in 10 deaths. * In April 1998, drummer Cozy Powell died following a car accident on the M4 near Bristol. * In July 2002,

Gus Dudgeon Angus Boyd "Gus" Dudgeon (30 September 1942 – 21 July 2002) was an English record producer, who oversaw many of Elton John's most acclaimed recordings, including his commercial breakthrough, " Your Song". Their collaboration led to seven US N ...

, a music producer known for his work with

Elton John Sir Elton Hercules John (born Reginald Kenneth Dwight; 25 March 1947) is a British singer, pianist and composer. Commonly nicknamed the "Rocket Man" after his 1972 hit single of the same name, John has led a commercially successful career a ...

, and his wife died when the car he was driving veered off the M4 between Reading and Maidenhead. The inquest recorded a verdict of accidental death.

References

External links

CBRD Motorway Database – M4

British Road Database: Motorways – M4 Junction 8/9
* The Motorway Archive *

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Map of the preferred route around Newport (relief road)
{{DEFAULTSORT:4-0004m Constituent roads of European route E30 Motorways in England Motorways in London Motorways in Wales Roads in Berkshire Roads in Bristol Transport in Bridgend County Borough Transport in Cardiff Transport in Carmarthenshire Transport in the London Borough of Hillingdon Transport in the London Borough of Hounslow Transport in Monmouthshire Transport in Neath Port Talbot Transport in Newport, Wales Transport in Rhondda Cynon Taf Transport in South Gloucestershire District Transport in Swansea Transport in Wiltshire

History

After completion

Former bridge tolls

Timeline of construction

Maintenance

Features

Speed limits

Smart motorway

Brynglas tunnels

Bus lane

Porous road surface

Elevated and heated section

Four level stack interchanges

Notable junctions

Relief road

List of junctions

E30

Major incidents and accidents

See also

References

Further reading

External links