M4

Easily one of the most varied motorways in Britain, from urban chaos in west London and Heathrow Airport, out through the rolling hills of Gloucestershire, across the Severn Estuary and through industrial South Wales, the M4 does it all.

In the nineteenth century, one of the first great inter-city railways was the Great Western, linking London to Bristol, South Wales and the West. The M4 is, effectively, the Great Western motorway, doing exactly that job but for the modern era. From suburban London it follows the Thames Valley past Slough, Maidenhead and Reading - home, today, of Britain's technology companies, and a place that has earned the M4 the nickname the "silicon highway". Beyond Reading the commuter traffic drops away and a long, smooth run through rural Wiltshire delivers the motorway to Bristol, where the traffic is never less than busy.

Before the M4 Severn Bridge was built, there was no road crossing of the Severn south of Gloucester, meaning that traffic between South Wales and southern England had to drive the A40, far out of its way to the north and frequently congested at Gloucester, or go via Bristol and Chepstow, choosing between the Severn ferry or the railway tunnel. The train and boat options were not particularly well used by motor traffic, but the bridge certainly is today, which suggests that the lack of a decent crossing was preventing a great number of journeys from happening at all.

In 1996, the Second Severn Crossing opened, carrying a widened and improved M4 over the estuary. The original Severn Bridge and Wye Bridge, along with a substantial length of ex-M4 at each side, now form the M48. Built and opened as part of the Second Severn Crossing project, the M49 was designed to reduce congestion at the M5 junction, cutting the corner between the south-west, Bristol and the new bridge. Because of these multiple motorway connections (M48, M49, M48 again, M5 and M32), the M4 holds the UK record of five consecutive motorway-to-motorway interchanges.

Given that the first section of this motorway was opened in 1959 - the Chiswick Flyover, which was initially part of the A4 but was designed to become part of the motorway a few years later - it is surprising to learn that it remained in two disconnected parts until 1994. Plugging the gap was a six-mile section of the A48 at Briton Ferry in South Wales, with a motorway bypass delayed again and again due to the difficult marshy land and a navigable river. The problem was only solved very late in the day with a large and expensive viaduct over the top of the whole thing, the opening of which finally completed the motorway between London and Swansea.

Start

London

End

Pont Abraham

Passes

Hounslow, Heathrow Airport, Slough, Maidenhead, Reading, Newbury, Swindon, Chippenham, Bristol, Newport, Cardiff, Bridgend, Port Talbot, Swansea

Length

192 miles

Click a section name to see its full details, or click a map symbol on the right to see all motorways opened in that year.

Completed Name Start End Original number
Chiswick Flyover J1 Chiswick Great West Road A4 Chronology map for 1959
Maidenhead Bypass J7 Huntercombe J8/9 Holyport Chronology map for 1961
Slough Bypass J5 Langley J7 Huntercombe Chronology map for 1963
Chiswick - Langley Great West Road J5 Langley Chronology map for 1965
Port Talbot Bypass J39 Groes J41 Baglan A48(M) Chronology map for 1966
Hambrook - Aust J19 Hambrook J21 Awkley Chronology map for 1966
Tormarton - Hambrook J18 Tormarton J19 Hambrook Chronology map for 1966
Crick - Coldra J23 Rogiet J24 Coldra Chronology map for 1967
Newport Bypass J24 Coldra J28 Tredegar Park Chronology map for 1967
Stanton St Quintin - Tormarton J17 Stanton St Quintin J18 Tormarton Chronology map for 1971
Badbury - Spittleborough J15 Plough Hill J16 Spittleborough Chronology map for 1971
Spittleborough - Stanton St Quintin J16 Spittleborough J17 Stanton St Quintin Chronology map for 1971
Holyport - Badbury J8/9 Holyport J15 Plough Hill Chronology map for 1971
Morriston and Llansamlet Bypass J44 Lon-las J46 Llangyfelach Chronology map for 1972
Pontarddulais Bypass J46 Llangyfelach J49 Pont Abraham Chronology map for 1977
Tredegar Park - St Mellons J28 Tredegar Park J29 Castleton Chronology map for 1977
Pyle Bypass J37 Pyle J39 Groes Chronology map for 1977
Coryton - Pencoed J32 Coryton J35 Pencoed Chronology map for 1977
Castleton - Coryton J29 Castleton J32 Coryton Chronology map for 1980
Bridgend Bypass J35 Pencoed J37 Pyle Chronology map for 1981
Earlswood - Lon-las J42 Earlswood J44 Lon-las Chronology map for 1993
New Briton Ferry Bridge J41 Pentyla J42 Earlswood Chronology map for 1994
Second Severn Crossing J21 Awkley J23 Rogiet Chronology map for 1996

Exit list

Symbols and conventions are explained in the key to exit lists. You can click any junction to see its full details.

Junction   Eastbound               Westbound  
1
12.4 km
Central London
Hammersmith
A4


A315

A406
EAST
A4


A205
N/A
LanesLanesLanesLanesLanes SignsSigns LanesLanesLanesLanesLanes SignsSigns
1 mile, 2 lanes 1 mile, 2 lanes
2
13.4 km
North Circular Road
A406 Link
South Circular Road
A205
Chiswick
A315


A4
Staines
Hounslow
A4
LanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
16.0 km
LanesLanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
3 miles, 3 lanes 3 miles, 3 lanes
20.5 km Services Heston Services Heston
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
1 mile, 3 lanes 2 miles, 3 lanes
3
22.0 km
Heathrow Airport
Harrow
Hounslow
A312
A312 A312 Heathrow Airport T4 & Cargo
Feltham
Hayes
A312
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
2 miles, 4 lanes 2 miles, 4 lanes
4
25.0 km
Uxbridge
Heathrow Airport T2 & 3
A408
(A408) (A4) Heathrow Airport T2 & 3
Uxbridge
A408
LanesLanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanesLanes Signs
2 miles, 5 lanes 2 miles, 5 lanes
4B
27.5 km
Watford (M1 Link)
Oxford (M40 Link)
(M3 Link)
Gatwick Airport
Heathrow Airport T4, 5 & Cargo
M25 Link
M25
(M1)
(M40)
M25
(M3)
(M23)
(M3 Link)
Gatwick Airport
Heathrow Airport T4, 5 & Cargo
Watford (M1 Link)
Oxford (M40 Link)
M25 Link
LanesLanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanesLanes Signs
1.6 miles, 5 lanes  
30.3 km
LanesLanesLanesLanesLanesLanes
0.4 miles, 4 lanes 2 miles, 4 lanes
5
31 km
Langley
Colnbrook
A4
Datchet
Eton B470
A4 A4
(A3044)
B470
Langley
Colnbrook
A4
Datchet
B470
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
4 miles, 4 lanes 4 miles, 4 lanes
6
37 km
Slough (C)
A335
Windsor
(A332)
A335 A335 Slough (C)
A335
Windsor
(A332)
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
2 miles, 4 lanes 2 miles, 4 lanes
7
40 km
Slough (W)
A4
(A4) Slough (W)
A4
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
4 miles, 4 lanes  
River or canal River Thames River or canal River Thames
  4 miles, 4 lanes
8/9
45 km
High Wycombe
A404(M) Link
Maidenhead
A308(M) Link
A308(M)

A404(M)
High Wycombe
A404(M) Link
Maidenhead
A308(M) Link
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
7 miles, 4 lanes 7 miles, 4 lanes
10
57 km
Reading (E)
Wokingham
Bracknell
A329(M) Link
A329(M) A329(M) Reading (E)
Wokingham
Bracknell
A329(M) Link
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
6 miles, 4 lanes 6 miles, 4 lanes
11
66 km
Reading (C & S)
Basingstoke
A33
B3270
B3031
A33
A33 Reading (C & S)
Basingstoke
A33
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
3 miles, 4 lanes 3 miles, 4 lanes
70.2 km Services Reading Services Reading
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
2 miles, 4 lanes 2 miles, 4 lanes
12
73 km
Theale
Reading (W)
A4
A4 A4 Theale
Reading (W)
A4
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
12 miles, 3 lanes 12 miles, 3 lanes
13
92 km
Newbury
Oxford
A34
Services Chieveley



A34



A34
Newbury
Oxford
A34
Services Chieveley
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
8 miles, 3 lanes 8 miles, 3 lanes
14
104 km
Hungerford
Wantage
A338
A338 A338 Hungerford
Wantage
A338
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
4 miles, 3 lanes 4 miles, 3 lanes
110 km Services Membury Services Membury
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
8 miles, 3 lanes 8 miles, 3 lanes
15
123.5 km
Marlborough
A346
Swindon (E)
A419 Link
Oxford (A420)
A419
(A420)
A346 Marlborough
A346
Swindon
A419 Link
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
6 miles, 3 lanes 6 miles, 3 lanes
16
132.5 km
Swindon (W)
Royal Wootton Bassett
RAF Lyneham
Calne
A3102
A3102 B4005

A3102
Swindon (W)
Royal Wootton Bassett
RAF Lyneham
Calne
A3102
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
12 miles, 3 lanes 12 miles, 3 lanes
17
153 km
Cirencester
A429
Chippenham
A350
A429 B4122

A350
Cirencester
A429
Chippenham
A350
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
2 miles, 3 lanes 2 miles, 3 lanes
155.5 km Services Leigh Delamere Services Leigh Delamere
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
9 miles, 3 lanes 9 miles, 3 lanes
18
169.5 km
Bath
Stroud
A46
A46 A46 Bath
Stroud
A46
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
7 miles, 3 lanes 7 miles, 3 lanes
19
181.5 km
Bristol
M32 Link
M32 Bristol
M32 Link
LanesLanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanesLanes Signs
3 miles, 3 lanes + HSR 3 miles, 3 lanes + HSR
20
186.5 km
The MIDLANDS
Gloucester
The SOUTH WEST
Bristol & Airport
M5 Link
M5 M5 The SOUTH WEST
Bristol (W)
The MIDLANDS
Gloucester
M5 Link
LanesLanesLanesLanesLanesLanes
LanesLanesLanesLanesLanes Signs
LanesLanesLanesLanesLanesLanes Signs
2 miles, 3 lanes 2 miles, 2 lanes
21
189.5 km
M48 Chepstow
M48 Link
LanesLanesLanesLanesLanes LanesLanesLanesLanes
3 miles, 2 lanes 3 miles, 2 lanes
22
195.5 km
The SOUTH WEST
Avonmouth
M49 Link (M5 Link)
M49 Avonmouth
M49 Link
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
7 miles, 3 lanes  
River or canal River Severn
Welcome to England
River or canal River Severn
Croeso i Gymru
Welcome to Wales
  6 miles, 3 lanes
23 Cas-gwent
Chepstow
M48 Link
M48
LanesLanesLanesLanesLanes
1 mile, 3 lanes 2 miles, 3 lanes
23A Caldicot
Magwyr
Magor
A4810
Services Magor
A4810 Magwyr
Magor
Caldicot
A4810
Services Magor
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
4 miles, 3 lanes 4 miles, 3 lanes
24 CANOLBARTH LLOEGR
The MIDLANDS
Trefynwy
Monmouth
A449 (M50) Link
Casnewydd
Newport A48
A48

A449
A48

B4237
Casnewydd (Dn)
Newport (E) A48
Trefynwy
Monmouth
A449 Link
LanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanes Signs
4.25 miles, 3 lanes 3 miles, 3 lanes
25 B4596 B4596 Caerleon
B4596
LanesLanesLanesLanesLanes
  0.25 miles, 3 lanes
25A River or canal Usk A4042

Casnewydd
Newport
Cwmbran
A4042
River or canal Usk
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
1 mile, 2 lanes  
Brynglas Tunnels Brynglas Tunnels
  1 mile, 2 lanes
26 Cwmbran
Casnewydd
Newport
Caerleon
A4051
A4051 A4051 Casnewydd
Newport
A4051
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
2 miles, 3 lanes 2 miles, 3 lanes
27 High Cross
B4591
B4591 B4591 High Cross
B4591
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
1 mile, 3 lanes 1 mile, 3 lanes
28 Casnewydd
Newport A48
Risca
Brynmawr
A467
A467

A48

A48
Casnewydd
Newport A48
Risca
Brynmawr
A467
LanesLanesLanesLanesLanes Signs LanesLanesLanesLanesLanes Signs
5 miles, 3 lanes 2 miles, 3 lanes
29 A48(M) Caerdydd (Dn a D)
Cardiff (E & S)
A48(M) Link
LanesLanesLanesLanesLanes
  3 miles, 3 lanes
30 Caerdydd (Dn)
Cardiff (E)
A4232
Services Cardiff Gate
A4232

Caerdydd (Dn)
Cardiff (E)
A4232
Services Cardiff Gate
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
5 miles, 3 lanes 5 miles, 3 lanes
32 Caerdydd (G)
Cardiff (N)
Merthyr Tudful
Merthyr Tydfil
A470
A4054


A470





A470

A4054
Caerdydd (G)
Cardiff (N)
Merthyr Tudful
Merthyr Tydfil
A470
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
3 miles, 3 lanes 3 miles, 3 lanes
33 Caerdydd (Gn) a Airport
Cardiff (W) & Airport
Barri
Barry
Penarth
A4232
Services Cardiff West
A4232 Caerdydd (Gn) a Airport
Cardiff (W) & Airport
Barri
Barry
Penarth
A4232
Services Cardiff West
LanesLanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
2 miles, 4 lanes 2 miles, 3 lanes
34 Llantrisant
Rhondda
A4119
A4119 Llantrisant
Rhondda
A4119
LanesLanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
6 miles, 3 lanes 6 miles, 3 lanes
35 Pen-y-bont
Bridgend
Pen-coed
A473
A473 A473 Pen-y-bont
Bridgend
Pen-coed
A473
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
4 miles, 3 lanes 4 miles, 3 lanes
36 Pen-y-bont
Bridgend
A4061
Maesteg
A4063
Services Sarn Park
A4061
A4063

A4061 Pen-y-bont
Bridgend
A4061
Maesteg
A4063
Services Sarn Park
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
6 miles, 3 lanes 6 miles, 3 lanes
37 Pîl
Pyle
Porthcawl
A4229
A4229
(A48)
A4229 Pîl
Pyle
Porthcawl
A4229
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
3 miles, 3 lanes 3 miles, 3 lanes
38 Port Talbot
A48
A48 Port Talbot
A48
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
4 miles, 2 lanes  
39 A4241

A48
  4 miles, 2 lanes
40 Port Talbot
A4107
A4107 A4107 Port Talbot
A4107
LanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
1 mile, 2 lanes  
41 Port Talbot
A48
A48 B4286

A48
LanesLanesLanesLanes
1 mile, 2 lanes 2 miles, 2 lanes
41 (A48) Llansawel
Briton Ferry
A48
Signs LanesLanesLanesLanes Signs
3 miles, 2 lanes  
River or canal Afon Nedd
River or canal River Neath
River or canal Afon Nedd
River or canal River Neath
  3 miles, 2 lanes
42 A483 A483 Abertawe
Swansea
Vehicle Ferry
A483
LanesLanesLanesLanes
   
42 Llansawel
Briton Ferry A48
Abertawe
Swansea A483
(A48)
(A483)
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
2 miles, 3 lanes 2 miles, 3 lanes
43 Castell-nedd
Neath
Merthyr Tudful
Merthyr Tydfil
A465
A465 B4290 Castell-nedd
Neath
Merthyr Tudful
Merthyr Tydfil
A465
LanesLanesLanesLanesLanes LanesLanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
44 Abertawe (D)
Swansea (E)
A48
A4230

B4291
A48

B4625
Abertawe (D)
Swansea (E)
A48
LanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
45 Abertawe (G)
Swansea (N)
Pontardawe
A4067
A4067

B4603
A4067

B4603
Abertawe (G)
Swansea (N)
Pontardawe
A4067
LanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
46 Llangyfelach
Felindre
B4489
A48
B4489
A48
Llangyfelach
Felindre
B4489
LanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
47 Abertawe (Gn)
Swansea (W) A483
Services Swansea
A48
A483
A48
Abertawe (Gn)
Swansea (W) A483
Services Swansea
LanesLanesLanesLanes LanesLanesLanesLanes
4 miles, 2 lanes  
River or canal Afon Llwchwr
River or canal River Loughor
River or canal Afon Llwchwr
River or canal River Loughor
  4 miles, 2 lanes
48 Pontarddulais
Llanelli
A4138
A4138 A4138 Pontarddulais
Llanelli
A4138
LanesLanesLanesLanes LanesLanesLanesLanes
3 miles, 2 lanes 3 miles, 2 lanes
49
35.3 km
N/A A48


A483











A48
WEST
Services Pont Abraham
Caerfyrddin
Carmarthen A48
Rhydaman
Ammanford
Llandeilo
A483
Pontarddulais A48
LanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
Routes
M4

Picture credits

With thanks to Maurice Turner, Michael Young, Dave Ross, Chris Jackson, Steve, Chris McKenna, Chris Boots, Tim Lidbetter, Neil Padgen, Jonathan, Chris Clifford, Chris (a different one) and Martin Wareham for information on this page.

In this section

What's new

Sorry, wrong number

Road numbering is a system with clear rules. What happens when the people responsible for numbering roads don't follow them?

We need to talk about Wisley

National Highways are spending a third of a billion pounds rebuilding one of the most congested junctions on the M25. Is it money well spent?

Oxford's Ground Zero

Oxford's Zero Emission Zone is just a trial, but transport policy in Oxford has become the catalyst for pitched battles and drawn in protestors from across the UK. What's happening to this genteel university town?

Share this page

Have you seen...

Gateshead Highway

The unloved and unfinished Gateshead Highway is due to be demolished. Take a look at the road that Gateshead can't wait to get rid of.

About this page

Published

Last updated