Junctions
| M4 motorway | |||||
| km | Eastbound exits (B Carriageway) | Junction | Westbound exits (A Carriageway) | ||
|---|---|---|---|---|---|
| Road becomes A4 to Central London | J1 |
North Circular A406 South Circular A205 Chiswick A315 Non-motorway traffic |
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| 11.8 | A4 from Central London becomes the M4 Start of motorway |
||||
| 13.4 13.7 |
North Circular A406 South Circular A205 Chiswick A315 |
J2 | Staines, Hounslow, Brentford A4 | ||
| Heston services | Services | Heston services | |||
| 21.5 22.1 |
Heathrow (Terminals 4, 5 & Cargo), Hayes, Harrow, Hounslow A312 | J3 | Heathrow (Terminals 4, 5 & Cargo), Hayes, Harrow, Hounslow A312 | ||
| 24.5 25.2 |
Heathrow (Terminals 1, 2 & 3) (A4) Uxbridge (A408) |
J4a | Heathrow (Terminals 1, 2 & 3) (A4) Uxbridge (A408) |
||
| 27.0 28.5 |
Heathrow (Terminals 4, 5 & Cargo), Gatwick Airport, Watford, Oxford, Stansted Airport (M40, M1, M11, M3, M23) M25 | J4b |
Heathrow (Terminals 4, 5 & Cargo), Gatwick Airport, Maidstone, Watford, Oxford, Stansted Airport (M40, M1, M11, M3, M23, M20) M25 | ||
| 30.7 31.4 |
Colnbrook, Langley A4 Eton, Datchet B470 |
J5 | Colnbrook, Langley A4, Datchet B470 | ||
| 36.8 37.4 |
Slough (Central) A355 Windsor A322 |
J6 | Slough (Central) A355 Windsor A322 |
||
| 39.8 40.3 |
Slough (West) A4 | J7 | Slough (West) A4 | ||
| 44.7 45.4 |
High Wycombe, Henley A404(M) Maidenhead A308(M) |
J8/9 | High Wycombe, Henley A404(M) Maidenhead A308(M) |
||
| 56.4 57.6 |
Reading (East), Wokingham, Bracknell A329(M) | J10 | Reading (East), Wokingham, Bracknell A329(M) | ||
| 65.4 66.3 |
Basingstoke, Reading (Central) A33 | J11 | Basingstoke, Reading (C & S) A33 | ||
| Reading services | Services | Reading services | |||
| 72.9 73.5 |
Reading (West), Theale A4 | J12 | Reading (West), Theale A4 | ||
| 91.5 92.1 |
Newbury, Oxford A34 Chieveley services |
J13 Services |
Newbury, Oxford A34 Chieveley services |
||
| 103.7 104.3 |
Hungerford, Wantage A338 | J14 | Hungerford, Wantage A338 | ||
| 110.5 | Membury services | Services | Membury services | ||
| 122.9 124.0 |
Swindon (East) A419 Marlborough A346 Oxford (A420) |
J15 | Swindon A419, Marlborough A346 | ||
| 132.6 133.2 |
Swindon (West), Royal Wootton Bassett, RAF Lyneham, Calne A3102 | J16 | Swindon (West), Royal Wootton Bassett, RAF Lyneham, Calne A3102 | ||
| 152.5 153.4 |
Chippenham A350 Cirencester A429 |
J17 | Chippenham A350 Cirencester A429 |
||
| 155.7 | Leigh Delamere services | Services | Leigh Delamere services | ||
| 168.8 170.0 |
Bath, Stroud A46 | J18 | Bath, Stroud A46 | ||
| 181.5 182.1 |
Bristol M32 | J19 | Bristol M32 | ||
| 186.3 187.2 |
The SOUTH WEST, Bristol (West), The MIDLANDS, Gloucester M5 Almondsbury Interchange |
J20 |
The SOUTH WEST, Bristol (West) M5(S) The MIDLANDS, Gloucester M5(N) |
||
| 189.5 190.0 |
No access | J21 | Chepstow M48 | ||
| 195.2 195.7 |
Avonmouth M49 The SOUTH WEST, Bridgwater, Exeter (M5 South) |
J22 | Avonmouth M49 | ||
| 195.9 199.8 |
Entry into England | Second Severn Crossing |
Entry into Wales | ||
| 204.4 | No tolls | Tolls | Toll booth | ||
| 208.0 | Chepstow M48 | J23 | No access | ||
| 211.4 212.8 |
Magor, Caldicot B4245 Magor services |
J23a Services |
Magor, Caldicot B4245 Magor services |
||
| 217.0 218.3 |
City centre A48 Newport (East) B4237 Monmouth A449 The MIDLANDS (M50) |
J24 | City centre A48 Newport (East) B4237 Monmouth A449 |
||
| 222.0 | No access | J25 | Caerleon B4596 | ||
| 222.6 | No access | J25a | Newport, Cwmbran A4042 | ||
| 223.4 223.8 |
Brynglas Tunnels | Tunnel | Brynglas Tunnels | ||
| 223.8 224.5 |
Newport, Cwmbran, Caerleon A4051 | J26 | Newport A4051 | ||
| 226.6 227.6 |
High Cross B4591 | J27 | High Cross B4591 | ||
| 228.5 230.0 |
Newport A48 Risca, Brynmawr A467 |
J28 | Newport A48 Risca, Brynmawr A467 |
||
| 231.1 | No access | J29 | Cardiff East and South A48(M) | ||
| 236.0 237.0 |
Cardiff East A4232 Cardiff Gate services |
J30 Services |
Cardiff East A4232 Cardiff Gate services |
||
| 244.5 246.1 |
Cardiff North, Merthyr Tydfil A470 | J32 | Cardiff North, Merthyr Tydfil A470 | ||
| 250.1 251.1 |
Cardiff West, Cardiff International Airport, Barry, Penarth A4232 Cardiff West services |
J33 Services |
Cardiff West, Cardiff International Airport, Barry, Penarth A4232 Cardiff West services |
||
| 253.5 254.4 |
Llantrisant, Rhondda A4119 | J34 | Llantrisant, Rhondda A4119 | ||
| 263.7 264.5 |
Pen-coed A473 | J35 | Pen-coed, Bridgend A473 | ||
| 269.6 270.8 |
Bridgend A4061 Maesteg A4063 Sarn Park services |
J36 Services |
Bridgend A4061 Maesteg A4063 Sarn Park services |
||
| 278.1 279.3 |
Porthcawl, Pyle A4229 | J37 | Porthcawl, Pyle A4229 | ||
| 284.9 285.3 |
Port Talbot A48 | J38 | Port Talbot A48 | ||
| 286.9 | No access (on-ramp only) | J39 | No access | ||
| 289.2 289.6 |
Port Talbot A4107 | J40 | Port Talbot A4107 | ||
| 291.1 291.8 |
Port Talbot A48 | J41 | Port Talbot, Baglan A48 | ||
| 295.9 297.3 |
Swansea A483 Briton Ferry A48 |
J42 | Swansea A483 | ||
| 297.5 298.8 |
Neath, Merthyr Tydfil A465 | J43 | Neath, Merthyr Tydfil A465 | ||
| 300.9 301.6 |
Swansea A48 | J44 | Swansea A48 | ||
| 303.9 304.7 |
Swansea, Pontardawe, Morriston, Clydach A4067 | J45 | Swansea, Pontardawe, Morriston, Clydach A4067 | ||
| 307.0 308.0 |
Swansea, Llangyfelach B4489 | J46 | Swansea, Llangyfelach B4489 | ||
| 309.6 310.7 |
Swansea A483 Pontarddulais A48 Penllergaer, Gorseinon A4240 Swansea services |
J47 Services |
Swansea A483 Pontarddulais A48 Penllergaer, Gorseinon A4240 Swansea services |
||
| 316.0 317.2 |
Pontarddulais, Llanelli A4138 | J48 | Pontarddulais, Llanelli A4138 | ||
| 320.6 | Start of motorway | J49 Terminus Services |
Carmarthen A48 Ammanford A483 Pont Abraham services |
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| 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. | |||||
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- Coordinate list
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