M4 motorway
- The M4 motorway is also a motorway in the Republic of Ireland, on the route from Dublin to Sligo. See N4 road and Roads in Ireland.
The M4 motorway is a motorway in the UK, which links London and Wales via Bristol.
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Westbound
- Start of motorway A4 main line becomes M4. The A4 continues below the flyover.
- 1: No exit
- 2: A4 Staines, Hounslow.
- Heston services
- 3: A312 Heathrow Airport Terminal 4 and cargo, Hayes, Harrow, Feltham.
- 4: M4 spur Heathrow Airport terminals 1, 2 & 3, A408 Uxbridge. Access via spur to Junction 4a and A4 east and west.
- 4b: M25 Heathrow Airport Terminal 4 and cargo, Gatwick Airport, Watford, Oxford.
- 5: A4 Colnbrook, Langley, B470 Datchet.
- 6: A355 Slough central, A332 Windsor.
- 7: A4 Slough west.
- 8/9: A404(M) High Wycombe, Henley, A308M Maidenhead.
- 10: A329(M) Reading east, Wokingham, Bracknell.
- 11: A33 Basingstoke, Reading central and south.
- Reading services
- 12: A4 Theale, Reading west.
- 13: A34 Newbury, Oxford. Chieveley services
- 14: A338 Hungerford, Wantage.
- Membury services
- 15: A346 Marlborough, A419 Swindon, Gloucester.
- 16: A3102 Swindon west, Wootton Bassett, Calne.
- 17: A350 Chippenham, A429 Cirencester.
- Leigh Delamere services
- 18: A46 Bath, Stroud.
- 19: M32 Bristol.
- 20: M5 The south west, Bristol west, The midlands, Gloucester.
- 21: M48 Chepstow (the original line of the M4)
- 22: M49 Avonmouth.
- 23: No exit
- 23a: B4245 Magor, Caldicot. Magor services
- 24: A48/B4237 Newport east, A449 Monmouth.
- 25: B4596 Caerleon.
- 25a: A4042 Newport, Cwmbran.
- 26: A4051 Newport.
- 27: B4591 High Cross.
- 28: A48 Newport, A467 Risca, Brynmawr.
- 29: A48(M) Cardiff east and south.
- 30: A4232 Cardiff east.
- There is no Junction 31
- 32: A470 Cardiff north, Merthyr Tydfil.
- 33: A4232 Cardiff west, Barry, Penarth, airport. Cardiff West services
- 34: A4119 Llantrisant, Rhondda.
- 35: A473 Bridgend, Pen-coed.
- 36: A4061 Bridgend, A4063 Maesteg. Sarn Park services
- 37: A4229 Porthcawl, Pyle.
- 38: A48 Port Talbot.
- 39: No exit
- 40: A4107 Port Talbot.
- 41: A48 Briton Ferry.
- 42: A483 Swansea and ferry.
- 43: A465 Neath, Merthyr Tydfil.
- 44: A48 Swansea east.
- 45: A4067 Swansea, Pontardawe.
- 46: B4489 Swansea north.
- 47: A483 Swansea west, A48 Pontarddulais. Swansea West services
- 48: A4138 Pontarddulais, Llanelli.
- 49: End of motorway A48 Carmarthen, Pontarddulais, A483 Ammanford. Pont Abraham services
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Eastbound
- Start of the motorway. Pont Abraham services. A48 Carmarthen, Pontarddulais, A483 Ammanford.
- Junction 48: A4138 Pontarddulais, Llanelli.
- Junction 47: Swansea West services. A483 Swansea west.
- Junction 46: B4489 Swansea north.
- Junction 45: A4067 Swansea, Pontardawe.
- Junction 44: A48 Swansea east.
- Junction 43: A465 Neath, Merthyr Tydfil.
- Junction 42: A483 Swansea and ferry, A48 Briton Ferry.
- Junction 41: A48 Port Talbot.
- Junction 40: A4107 Port Talbot.
- There is no Junction 39
- Junction 38: A48 Port Talbot.
- Junction 37: A4229 Porthcawl, Pyle.
- Junction 36: Sarn Park services. A4061 Bridgend, A4063 Maesteg.
- Junction 35: A473 Pen-coed.
- Junction 34: A4119 Llantrisant, Rhondda.
- Junction 33: Cardiff West services. A4232 Cardiff west, Barry, Penarth, airport.
- Junction 32: A470 Cardiff, Merthyr Tydfil.
- There is no Junction 31
- Junction 30: A4232 Cardiff east.
- Junction 29: No exit.
- Junction 28: A48 Newport, A467 Risca, Brynmawr.
- Junction 27: B4591 High Cross.
- Junction 26: A4051 Newport, Cwmbran, Caerleon.
- Junction 25a: No exit
- Junction 25: No exit
- Junction 24: M50 The Midlands, A48/B4237 Newport, A449 Monmouth.
- Junction 23a: Magor services. B4245 Magor, Caldicot.
- Junction 23: M48 Chepstow This is the old M4
- Second Severn Crossing (bridge).
- Junction 22: M49 Avonmouth, The south west.
- Junction 21: No exit
- Junction 20: M5 The south west, Bristol west, The midlands, Gloucester.
- Junction 19: M32 Bristol.
- Junction 18: A46 Bath, Stroud.
- Leigh Delamere services.
- Junction 17: A350 Chippenham, A429 Cirencester.
- Junction 16: A3102 Swindon west, Wootton Bassett, Calne.
- Junction 15: A346 Marlborough, A419 Swindon east. A420 Oxford.
- Membury services.
- Junction 14: A338 Hungerford, Wantage.
- Unnumbered junction reserved for military use, leading to RAF Welford
- Junction 13: A34 Newbury, Oxford, Chieveley services.
- Junction 12: A4 Theale, Reading west.
- Reading services.
- Junction 11: A33 Basingstoke, Reading central and south.
- Junction 10: A329(M) Reading east, Wokingham, Bracknell.
- Junction 8/9: A404(M) High Wycombe, Henley, A308(M) Maidenhead.
- Junction 7: A4 Slough west.
- Junction 6: A355 Slough central, A332 Windsor.
- Junction 5: A4 Colnbrook, Langley, B470 Eton, Datchet.
- Junction 4b: M25 Heathrow Airport Terminal 4 and cargo, Gatwick Airport, Watford, Oxford.
- Junction 4: M4 spur to Heathrow Airport terminals 1, 2 & 3, A408 Uxbridge, Hayes. Access via spur to Junction 4a and A4 east and west.
- Junction 3: A312 to Heathrow Airport Terminal 4 and cargo, Hayes, Harrow, Hounslow.
- Heston services.
- Junction 2 (restricted access): A205 South Circular, A406 North Circular, A315 Chiswick, A4.
- Junction 1: No exit
- The M4 ends six miles (10 km) west of central London where it becomes the A4.
Notes
In the construction of the section around Cardiff, when a section between Bridgend and Port Talbot already existed, numbers were set aside for intermediate interchanges. 33 had been set for the link road to the west (A4232), 32 for the A470, with 31 intended for the A469 to Caerphilly, and 30 for the great "Hook Road" - a plan which was later shelved. Junction 30 was later added to serve the link road in the east, which will eventually form a ring road from junctions 33 to 30, via Cardiff Bay. Number 31 remains unused as of 2005, and there are no immediate plans to build a junction with the A469.
Contrary to popular belief, junction 39 does exist, however, it consists of a single slip road completing the missing movement onto the westbound carriage way from the A48 at junction 38, thus there is no exit from the motorway at this junction.
Junction 41 refers to two different junctions in the two different directions, their movements not complementary. In the westbound direction, 41 is indicated as a spur leading to the roundabout in Briton Ferry formerly known as 41A, and the original bridge over the River Neath, which would allow access onto the stretch of the M4 from junction 43 westward. In the eastbound direction, 41 is indicated as an exit-only route to the A48 towards Port Talbot. As a result, it is possible in both directions to travel almost 2 miles (3 km) in the same direction having both joined and subsequently left the motorway at "junction 41".