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Road details
About the M4
Approximate length189 miles
RouteLondon – South Wales
Eastern endChiswick, London
Western endPont Abraham, Carmarthenshire
Major areasLondon, Reading, Swindon, Bristol, Newport, Cardiff, Swansea
Key connectionsM25, M32, M5, M48, M49, A48(M)
Connecting roads
M4 planned closures and diversions
M4 services
Motorway services guide →Selected service areas from operator listings. Check the operator for current facilities, access and opening times.
How busy is the M4?
2025 annual average156,491vehicles a day
local authority boundary to J4 · Hillingdon
6,249 HGVs a day · 4.0% of traffic
Busiest published count location · both directionsM4 route and junction details
Selected junctions and connections. Check signs for permitted movements and current access.
Almondsbury Interchange (M4 J20)
- Connects M5
Hambrook Interchange
- Connects M32
- Connects M48
- Connects M49
Prince of Wales Bridge
- Prince of Wales Bridge crosses between England and Wales. Welsh onward traffic coverage is separate.
M4 traffic questions
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Where can I find M4 services?
The services section above lists service areas on the M4.
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