|Location Map ( geo)|
|3-level stacked roundabout|
|M4, A470, A4054|
|Junctions related to the A470|
|Abercanaid Roundabout • Abercynon Roundabout • Bala Junction • Bridge Street Interchange • Broadway Interchange • Brynich roundabout • Cefn Coed Roundabout • Cemmaes Road Roundabout • Cross Foxes • Gabalfa Interchange • Gellideg roundabout • Glan Conwy Interchange • Glyntaff Interchange • Llangurig roundabout • Llanidloes roundabout • Llyswen junction • Mallwyd • Moat Lane Junction • Nantgarw Interchange • Rhyd-y-car roundabout • Taffs Well Interchange • Tarell roundabout • The Flourish • Upper Boat Interchange|
|Junctions related to the A4054|
|Glyntaff Interchange • Nantgarw Interchange • Pentrebach Roundabout • Taffs Well Interchange • Upper Boat Interchange|
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!
A simple grade separated junction was built in the early 1970s 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 five years.
The replacement junction was improved in the summer of 2014 with the addition of a short link road from the westbound M4 to the A470 north. This enables traffic to avoid several sets of lights around the roundabout.
|Merthyr Tydfil/Merthyr Tudful|
|Superstore/Archfarchnad, Forest Farm/Fferm y Fforest|