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 Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. The English section to the

Severn Bridge The Severn Bridge ( cy, Pont Hafren) is a motorway suspension bridge that spans the River Severn between South Gloucestershire in England and Monmouthshire in South East Wales. It is the original Severn road crossing between England and ...

was constructed between 1961 and 1971; the Welsh element was largely complete by 1980, though a non-motorway section around Briton Ferry 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_ ...

, toll-free since 17 December 2018, the motorway follows the

A48 A48 may refer to : * A48 motorway (France), a road connecting the A43 and Grenoble * A48 road (Great Britain), a road connecting Gloucester, England and Carmarthen, Wales * Autovía A-48, a motorway under construction connecting Cadiz and Algeciras ...

, 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 Cal ...

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 ...

. 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 M4, ...

Reading Reading is the process of taking in the sense or meaning of Letter (alphabet), letters, symbols, etc., especially by Visual perception, sight or Somatosensory system, touch. For educators and researchers, reading is a multifaceted process invo ...

, Swindon,

Bristol Bristol () is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city i ...

Newport Newport most commonly refers to: *Newport, Wales *Newport, Rhode Island, US Newport or New Port may also refer to: Places Asia *Newport City, Metro Manila, a Philippine district in Pasay Europe Ireland *Newport, County Mayo, a town on the ...

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 sout ...

and Swansea.

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 a ...

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

. The

by-pass, also built in the 1960s and now part of the M4, was originally the

A48(M) motorway The A48(M) motorway in Wales links Cardiff with Newport. It is a long M4 spur. At St Mellons, it runs continuously into the dual-carriageway A48 A48 may refer to : * A48 motorway (France), a road connecting the A43 and Grenoble * A48 road ...

, 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 west of Newport, and following the creation of the Welsh Office 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 Swindon) was opened to traffic. The Welsh section was largely completed between 1970 and 1980, though a non-motorway section remained across the Briton Ferry 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. 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 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 with hydrogen stations 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 and ...

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, 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 ...

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 roadway ...

and a new gyratory. 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 ...

pillbox 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 bir ...

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_ ...

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 State-owned enterprise, government-owned company charged with operating, maintaining and improving Roads in England, motorways and major A roads in England. It al ...

. The in Wales is the responsibility of the South Wales Trunk Road Agent.

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 carry the M4 under 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-largest ...

. 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 w ...

to junction 3 (A312), covering part of the journey between Heathrow Airport 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 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 from other vehicles and improved visibility. This special surface was publicised in an episode of the BBC's '' Tomorrow's World'' 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 ...

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 Be ...

, 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 surrounded by the Chiltern Hills, it is west-northwest of Charing Cross in London, south-southeast of Aylesbur ...

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-eas ...

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 E ...

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) The A404 is a road in the United Kingdom that starts at Paddington in London and terminates near Maidenhead in Berkshire. It is long. Route The road initially follows a course through north-west London via Harlesden, Wembley, Harrow, ...

, 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 co ...

. 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, 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 traditi ...

) 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) 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 coun ...

). 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 Briton Ferry, formerly known as junction 41a, and the original bridge over the River Neath, 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 roads 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 , image = , caption = , date_established = , country = Wales , address = , leader_title = First Minister () , appointed = First Minister approved by the Senedd, ceremonially appointed ...

scrapped the proposal for a proposed motorway south of

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

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 The South Circular Road (formally the A205 and often simply called the South Circular) in south London, England, is a major road that runs from the Woolwich Ferry in the east to the Chiswick Flyover in the west via Eltham, Lee Green, Catf ...

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 ...

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'' , ''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 * Ha ...

Harrow Harrow may refer to: Places * Harrow, Victoria, Australia * Harrow, Ontario, Canada * The Harrow, County Wexford, a village in Ireland * London Borough of Harrow, England ** Harrow, London, a town in London ** Harrow (UK Parliament constituency) ...

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 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 status in the United Kingdom, borough in Hertfordshire, England, 15 miles northwest of Central London, on the River Colne, Hertfordshire, River Colne. Initially a small market town, the Grand Junction Canal en ...

(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

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

'' , - style="text-align:center;" , 19.1
19.5 , 30.7
31.4 , Colnbrook, Langley, Slough (East) A4
Eton, Datchet B470 , J5 , Colnbrook, Langley, Slough (East) A4, Datchet B470 , - style="text-align:center;" , 22.9
23.2 , 36.8
37.4 , Slough (Central) A355
Windsor A322 , J6 , Slough (Central) A355
Windsor 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 ...

A308(M) , J8/9 ,

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

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 Maidenhe ...

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

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'' , ''Services'' , '' Reading services'' , - style="text-align:center;" , 45.3
45.7 , 72.9
73.5 , Reading (West), Theale A4 , J12 , Reading (West), Theale 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 Un ...

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

A34
'' Chieveley services ( 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 t ...

, Wantage A338 , J14 ,

, Wantage A338 , - style="text-align:center;" , 68.7 , 110.5 , ''

Membury services Membury services is a motorway service station on the M4 motorway, located on the original site of RAF Membury in the civil parish of Lambourn in the English county of Berkshire, on the edge of the border with Wiltshire, west of Junction 14. It ...

'' , ''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, Gloucestershir ...

'' , - style="text-align:center;" , 76.4
77.1 , 122.9
124.0 , Swindon (East) A419
Marlborough A346

( A420) , J15 , Swindon A419, Marlborough A346 , - style="text-align:center;" , 82.4
82.8 , 132.6
133.2 , Swindon (West), Royal Wootton Bassett, Wroughton, MoD Lyneham,

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), Royal Wootton Bassett, Wroughton, MoD Lyneham,

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 is ...

A350

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 ,

A350

, - 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. ...

'' , ''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 Gl ...

'' , - 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 Plac ...

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 ...

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 of t ...

, Bristol Airport 20 airtransportation

, 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 , Avonmouth 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 Caldicot may refer to: * Caldicot, Buckinghamshire * Caldicot, Monmouthshire * Caldicot (hundred) * Caldicot Castle, Monmouthshire * Caldicot railway station, a part of the British railway system * Caldicot RFC, a Welsh rugby union club * Caldico ...

A4810
'' Magor services'' , J23A
''Services'' , Magor,

A4810
'' Magor services'' , - style="text-align:center;" , 134.8
135.6 , 217.0
218.3 , City centre

(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

( M50) , J24 , City centre

(East) B4237

A449 , - 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 Rom ...

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

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 pr ...

A4042 The A4042 is a trunk road that runs from Abergavenny to Newport in south Wales. Route Starting at the junction of the A40 and A465 south of Abergavenny, the A4042 travels south towards Little Mill north of Pontypool. This section is a singl ...

, - style="text-align:center;" , 138.8
139.1 , 223.4
223.8 , '' Brynglas Tunnels'' , ''Tunnel'' , '' Brynglas Tunnels'' , - style="text-align:center;" , 139.1
139.5 , 223.8
224.5 ,

A4051 , J26 ,

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 ,

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 s ...

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 devel ...

A467 , J28 ,

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

A4232 The A4232, which is also known either as the Peripheral Distributor Road (PDR) ( cy, Ffordd Ddosbarthu Ymylol) or the Cardiff Link Road ( cy, Ffordd Gyswllt Caerdydd), is a distributor road in Cardiff, the capital of Wales. The first section ...

'' Cardiff Gate services'' , J30
''Services'' , Cardiff (East)

'' Cardiff Gate services'' , - 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 Ty ...

A470 , J32 , Cardiff (North),

A470 , - 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 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 wealthy seaside resort ...

Cardiff Airport 20 airtransportation

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

Cardiff Airport 20 airtransportation

'' Cardiff West services'' , - 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 ar ...

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 The A4119 links Tonypandy with Cardiff in South Wales. Route City and County of Cardiff The A4119 starts outside the Wales Millennium Centre at Cardiff Bay and proceeds through Butetown, Grangetown, Riverside and Cathedral Road in Cant ...

Royal Glamorgan Hospital , J34 ,

Royal Glamorgan Hospital , - style="text-align:center;" , , , style=background:skyblue , ''Entering South Glamorgan'' , , 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 The A4061 is the main road linking Bridgend with Hirwaun via the Ogmore and Rhondda Valleys in South Wales. It is a mix of streets connecting former mining communities, and mountain passes built as relief work for unemployed miners. The road ...

Maesteg Maesteg is a town and community in Bridgend County Borough, Wales. Maesteg lies at the northernmost end of the Llynfi Valley, close to the border with Neath Port Talbot. In 2011, Maesteg had a population of 20,612. The English translation ...

A4063 The A4063 links the town of Bridgend with Cymer in Wales. Settlements on route Settlements served by the route include: *Bridgend * Wild Mill * Pen-y-fai * Sarn * Aberkenfig * Tondu * Coytrahen *Llangynwyd *Cwmfelin *Maesteg Maesteg is a t ...

Princess of Wales Hospital
'' Sarn Park services'' , J36
''Services'' ,

Princess of Wales Hospital
'' Sarn Park services'' , - style="text-align:center;" , 172.8
173.5 , 278.1
279.3 , Pyle, Porthcawl A4229 , J37 , Porthcawl, 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'' , - style="text-align:center;" , 177.0
177.3 , 284.9
285.3 ,

, J38 ,

, - 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 A41 may refer to: * A41, War Office Inventions Branch * ''A41'' (album), a studio album by All-4-One * Queen's Pawn Game, Encyclopaedia of Chess Openings code * Samsung Galaxy A41, a smartphone * Vultee XA-41, an American World War II attack prot ...

, J40 ,

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

, J41 , Briton Ferry

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

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 ...

, J43 ,

, - style="text-align:center;" , 187.0
187.4 , 300.9
301.6 , Swansea (East)

, J44 , Swansea (East)

, - style="text-align:center;" , 188.8
189.3 , 303.9
304.7 , Pontardawe, Swansea (North) A4067 , J45 , Pontardawe, Swansea (North) A4067 , - style="text-align:center;" , 190.8
191.4 , 307.0
308.0 , Llangyfelach B4489
Felindre
Morriston Hospital , J46 , Llangyfelach B4489
Felindre
Morriston Hospital , - 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 S ...

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

'' Swansea services'' , - style="text-align:center;" , , , style=background:skyblue , ''Entering West Glamorgan'' , , 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 ...

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

Llanelli Llanelli ("St Elli's llan (placename element), Parish"; ) is a market town and the largest community in Carmarthenshire and the Preserved counties of Wales, preserved county of Dyfed, Wales. It is located on the Loughor estuary north-west of ...

A4138 , J48 , Pontarddulais,

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, ...

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. Acco ...

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 ...

includes most of the M4. The entire route runs between Cork 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 ...

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 kille ...

near

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

*

*

*

*

*

*
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