A48(M) (Llantrisant Radial)
|Cardiff West Interchange (ST089794)
|M4, A4119, A48, Western Tangential
|Route outline (key)
The Llantrisant Radial was a planned motorway intended to form the western half of a Cardiff Inner Bypass. It would have branched off the A48 immediately west of Gabalfa Interchange and followed one of two proposed routes towards M4 J33. It was in planning for five years starting in 1966 and finally dropped in 1971.
The road was initially proposed as part of Professor Buchanan's transportation study for Cardiff in 1966 where it wouldn't have connected directly to the M4 but instead joined a planned Barry-Llanstrisant Primary to the south of M4 J33. In 1968 Buchanan published a follow up to his 1966 report and the western end of the Llantrisant Radial was altered to connect directly to the M4.
The initial line of the route followed the railway line west of Gabalfa Interchange. Soon afterwards another potential route was found along the River Taff. These became known as the Buchanan and River Routes. There was very little in terms of engineering, environmental and property acquisition to separate the two routes which meant they were both pursued with equal priority throughout much of the road's design stage. Eventually though the River Route won out.
A factor that could potentially affect the Llantrisant Radial's junction at Radyr is the Western Tangential. Although the Western Tangential wasn't programmed for construction until much later the choice of two routes for the Llantrisant Radial and a proposed shopping development at Radyr meant preliminary designs were made for the junction with the Western Tangential. When the Llantrisant Radial was to open the junction would be a Diamond interchange serving the A4119. This would be the case whichever of the two routes was eventually chosen. Upon opening of the Western Tangential the junction would become a modified three level stacked roundabout. In the case of the Buchanan Route the existing diamond would close and become a simple bridge with access to the A4119 made from a fifth arm of the roundabout. In the case of the River Route the bridge for the existing diamond would be used for part of the roundabout and the east facing slips would close. It's not clear if new east facing slips or south facing slips to the Western Tangential would be provided.
The western end of the Llantrisant Radial is unclear. Reports mention a freeflow Y shaped connection with the M4 half a mile east of the J33 roundabout but no maps showing such a layout have so far been found. The only map known shows the merge at the roundabout but it's unclear if this design was ever pursued.
Unlike most of Cardiff's planned road network of the era the Llantrisant Radial was to be a trunk road under the responsibility of central government rather than the City of Cardiff. This was because it would have formed part of the main road corridor through South Wales until the M4 north of Cardiff was built. Traffic levels at the time suggested there was a lower percentage of through traffic compared to that starting or ending its journey in Cardiff. As a result the Llantrisant Radial together with Eastern Avenue would become an inner bypass for the city allowing uninterrupted traffic flow to the M4 on either side. This would be able to cope with traffic levels for some years before the M4 was required and afterwards would become a distributor for traffic within the city upon the M4's opening.
All this was not to be. In the summer of 1971 the government transferred responsibility of the Llantrisant Radial to the city and county councils. The government decided to bring forward plans to complete the M4 instead. The city was battling to get its own road built, the Hook Road, which was plagued by community opposition. It came as no surprise that soon after the Llantrisant Radial was passed to the local councils the road was scrapped. The Llantrisant Radial itself wasn't free of anger of local residents but it became clear that building roads of this nature through urban areas was becoming more difficult as the 1970s progressed and this may have been a factor for the government to concentrate on the rural M4 instead.