The M4 goes from Gunnersbury (in the west of London) to Pont Abraham (a few miles north of Swansea).
Junctions and service areas[]
- Junction 1: London, A4, A406, A205.
- Junction 2: Brentford, A4.
- Heston service area.
- Junction 3: Hounslow, A312.
- Junction 4: West Drayton, Heathrow Airport.
- Junction 4A: Heathrow Airport, A4.
- Junction 4B: M25.
- Junction 5: Langley, A4.
- Junction 6: Slough, Eton, Windsor.
- Junction 7: Burnham, Slough (west).
- Junction 8/9: Maidenhead, A308(M), A404(M).
- Junction 10: Bracknell, Reading (east), A329(M).
- Junction 11: Reading, A33.
- Reading service area.
- Junction 12: Theale, Reading (west).
- Junction 13: Newbury, Chieveley service area, A34.
- Junction 14: Hungerford.
- Membury service area.
- Junction 15: Swindon, Marlborough, A346.
- Junction 16: Swindon, Wootton Basset.
- Junction 17: Chippenham A350, [A429]].
- Leigh Delamere service area.
- Junction 18: Bath, Chipping Sodbury, A46.
- Junction 19: Bristol M32
- Junction 20: M5.
- Junction 21: M48.
- Junction 22: M49.
- Crosses River Severn on Second Severn Crossing into Wales
- Junction 23: M48.
- Junction 23A: Caldicot, Magor service area.
- Junction 24: Newport (east), A449.
- Junction 25: Newport.
- Junction 25A: Cwmbran, A4042.
- Junction 26: Newport, Cwmbran, A4042.
- Junction 27: Rogerstone.
- Junction 28: Newport (west).
- Junction 29: Cardiff (north-east), [[A48(M)].
- Junction 30: Cardiff (north-east).
- Junction 32: Cardiff, Caerphilly, [A470].
- Junction 33: Cardiff (west), Barry, Cardiff West service area), A4232.
- Junction 34: Llantrisant.
- Junction 35: Pencoad.
- Junction 36: Bridgend, Sarn Park service area.
- Junction 37: Pyle, Porthcawl.
- Junction 38: Margam Park.
- Junction 39: Margam.
- Junction 40: Taibach, Cwmafan.
- Junction 41: Port Talbot, A48.
- Junction 42: Briton Ferry, A48.
- Junction 43: Neath, A465.
- Junction 44: Birchgrove.
- Junction 45: Swansea.
- Junction 46: Swansea (north).
- Junction 47: Gorseinon, Swansea West service area.
- Junction 48: Llanelli, A4138.
- Junction 49: Ammanford, Carmarthen, Pont Abraham service area, A48, A483.
Notable Structures[]
- Crosses River Severn on Second Severn Crossing Bridge into Wales, one of the biggest cable stayed bridges in the country.
| Motorways | |
|---|---|
| Single-digit motorways: | M1 • M2 • M3 • M4 • M5 • M6 • M8 • M9 |
| Two-digit motorways | M10 • M11 • M18 • M20 • M23 • M25 • M26 • M27 • M32 • M40 • M42 • M45 • M48 • M49 • M50 • M53 • M54 • M55 • M56 • M57 • M58
M60 • M61 • M62 • M65 • M66 • M67 • M69 • M73 • M74 • M77 • M80 • M90 |
| Three-digit motorways | M180 • M181 • M271 • M275 • M602 • M606 • M621 • M876 • M898 |
| Converted A-roads | A1(M) • A3(M) • A38(M) • A48(M) • A57(M) • A58(M) • A64(M) • A66(M) • A74(M) • A167(M) • A194(M) • A308(M) |