Coryton Interchange
| Coryton Interchange Cyfnewidfa Coryton | |||
| Location Map ( geo) | |||
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| Location | |||
| Tongwynlais | |||
| County | |||
| Glamorgan | |||
| Highway Authority | |||
| Welsh Government | |||
| Junction Type | |||
| 3-level stacked roundabout | |||
| Roads Joined | |||
| M4, A470, A4054 | |||
| Junctions related to the A470 | |||
Glan Conwy Interchange • Brynich roundabout • Gabalfa Interchange • Abercynon Roundabout • Bala Junction • Abercanaid Roundabout • Cefn Coed Roundabout • Tarell roundabout • Moat Lane Junction • Cemmaes Road Roundabout • Mallwyd • Cross Foxes • Taffs Well Interchange • Nantgarw Interchange • Llyswen junction • Llanidloes roundabout • Gellideg roundabout • Rhyd-y-car roundabout • Bridge Street Interchange • Broadway Interchange • Glyntaff Interchange • Upper Boat Interchange • Llangurig roundabout • The Flourish • Waterloo Bridge (Caernarfonshire) • Pontybat Crossroads | |||
| Junctions related to the A4054 | |||
Coryton Interchange is junction 32 of the M4.
Home to what is one of the largest roundabouts in the UK. It is just under a mile all the way around and the A470 manages to cross below the circulatory carriageway at the eastern side, but above at the western side!
History
A simple grade separated junction was built in 1971 when the A470 was dualled towards Merthyr Tydfil which allows the A4054 to pass beneath. A pair of petrol stations on the A470 meant the northbound carriageway was built with a C/D lane to reduce weaving.
At the time it was known that the M4 would be built together with a replacement junction but it was expected that it would be some time into the future as the Llantrisant Radial would be built first. This, along with the A48 Eastern Avenue, would have formed a Cardiff Inner Bypass which would have coped with traffic levels at the time but the Llantrisant Radial was scrapped in 1971 and construction of the M4 around the north of Cardiff was brought forward instead. This meant the junction at Coryton would be replaced earlier than expected. The M4 to the west opened in 1977 and that to the east opened in 1980 giving the original junction a lifespan of around six years.
The replacement junction was improved in the summer of 2014 with the addition of a short traffic signal-controlled link road from the westbound M4 to the A470 north. This enables traffic to avoid several sets of lights around the roundabout.
Routes
| Route | To | Notes |
| Bridgend/Pen-y-bont | ||
| Newport/Casnewydd | ||
| Merthyr Tydfil/Merthyr Tudful | ||
| Cardiff/Caerdydd | ||
| Tongwynlais | ||
| Whitchurch/Eglwys Newydd | ||
| Superstore/Archfarchnad, Forest Farm/Fferm y Fforest |
