Trunk road running between
Gloucester,
Gloucestershire and
Carmarthen,
Carmarthenshire.
It passes through Chepstow and Newport in Monmouthshire, then Cardiff, Bridgend and Swansea in Glamorganshire.
This used to be the main thoroughfare through south Wales before the building of the M4 in the early 1960s.
Intersections:
- A466 at Chepstow
- M4/A449/A455 at M4 junction 24
- A455 at George Street Bridge East Side, Newport
- A4042 at George Street Bridge West Side, Newport
- M4/A467 at M4 junction 28
- A4232 at Pontprenna, Cardiff
- A4161 at Newport Road, Cardiff
- A469/A470 at Heath, Cardiff
- A4119 at Llandaff, Cardiff
- A4161 at Llandaff, Cardiff
- A4050/A4232 at Wenvoe
- A4226 at Bonvilston
- A4222 at Cowbridge
- A473 at Bridgend
- A4106 at Bridgend
- A4229 at Pyle
- M4 at junction 38
- M4 at junction 39
- A4107 at Neath
- A4241 at Neath
- A474 at Neath
- M4 at junction 42
- M4 at junction 44
- A4217 at Birchgrove, Swansea
- A4067 at Birchgrove, Swansea
- M4 at junction 46
- M4/A483 at M4 junction 47
- A4240 at Swansea West
- A4138 at Pontarddulais, Swansea
- M4/A483 at M4 junction 49.