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Cardiff West Interchange

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Cardiff West Interchange
Gorllewin Caerdydd
Location Map ( geo)
M4 at Junction 33 - Geograph - 4138284.jpg
Cameraicon.png View gallery (3)
Capel Llanilltern
Highway Authority
Welsh Government
Junction Type
Roundabout Interchange
Roads Joined
M4, A4232
Junctions related to the A4232

Cardiff West Interchange is junction 33 of the M4, serving the western side of Cardiff. It is also known as "Capel Llanilltern Interchange" (Cyfnewidfa Capel Llanilltern) (source:


Initial proposals

Early plan from the late 1960s but not the layout most likely to have been built

The junction was intended to connect the M4 to the Llantrisant Radial which would have provided access to Cardiff city centre from the west. The Llantrisant Radial was a trunk road in planning from 1968 to 1971 and was scrapped soon after. Several designs for the layout of the junction were planned but only two have surfaced. It is known the Llantrisant Radial was to freeflow to the M4 west and the most likely layout describes the Llantrisant Radial forming a Y junction about half a mile to the east of the roundabout. A plan of this layout has yet to be found. The Llantrisant Radial together with the A48 Eastern Avenue would have formed a Cardiff Inner Bypass and the M4 between J33 and J29 was to be built much later.

At the time of the Llantrisant Radial's planning there would also have been a connection to the A4119. The roundabout would have been situated around 200 metres east of its current position with a north facing link to the A4119.

The other road joining the roundabout was a planned Llantrisant-Barry Primary which would have been a dual carriageway of similar standard to the A4232 which was later built although serves a different purpose to the original plans.

Later plans

Following the abandonment of the Llantrisant Radial and the rest of Cardiff's ambitious urban motorway network the government decided to bring forward plans to construct the M4 north of Cardiff. The junction now planned was very much simplified and moved westwards along with a slight change to the alignment of the M4. During the second half of the 1970s a much reduced scheme to relieve central Cardiff of traffic was planned with just a single loop around the southern half of the city which opened as the A4232 although still incomplete. This heads south from Junction 33 along the route of the earlier planned Barry Primary. The link to the A4119 was never built and a service area now occupies the northern side of the roundabout although there is still space for a future link to the A4119.


Route To Notes






Cardiff West/Gorllewin Caerdydd, Barry/Barri, Airport/Maes Awyr, Penarth

Cardiff West services

Cardiff West services Gwasanaethau Gorllewin Caerdydd






Cardiff West Interchange
Related Pictures
View gallery (3)
M4 J33 early design.pngM4 J33 Eastbound - Capel Llanilltern Interchange - Coppermine - 5879.jpgM4 at Junction 33 - Geograph - 4138284.jpg
Other nearby junctions
Junctions on the M4
Main RouteChiswick • 2 Brentford • 3 Cranford Parkway • 4 Heathrow • 4B Colnbrook • 5 Langley • 6 Tuns Lane • 7 Huntercombe • 8/9 Holyport • 10 Winnersh • 11 Three Mile Cross • 12 Theale • 13 Chieveley • 14 Wickham • 15 Plough Hill • 16 Spittleborough • 17 Stanton St Quinton • 18 Tormarton • 19 Hambrook • 20 Almondsbury • 21 Awkley • 22 Pilning • 23 Rogiet • 23A Magor • 24 Coldra • 25 Caerleon • 25A Grove Park • 26 Malpas • 27 High Cross • 28 Tredegar Park • 29 Castleton • 30 Pentwyn • 31 Junction 31 • 32 Coryton • 33 Cardiff West • 34 Miskin • 35 Pencoed • 36 Sarn • 37 Pyle • 38 Margam • 39 Groes • 40 Taibach • 41 Pentyla • 42 Earlswood • 43 Llandarcy • 44 Lon-Las • 45 Ynysforgan • 46 Llangyfelach • 47 Penllergaer • 48 Hendy • 49 Pont Abraham
Heathrow SpurCherry Lane • 4 Heathrow • 4A Concord
Former RoutesBray • 9A Cox Green • 9B The Thicket // 19 Hambrook • 19A Frenchay // 20 Almondsbury • 21 Aust • 22 Newhouse • 23 Magor // 28  Tredegar Park • 29 St Mellons
Defunct Newport
Bypass Proposal
23 Rogiet • 25 Glan Llyn • 27 Dock Way • 29 Castleton

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