was a planned junction on the unbuilt Hook Road
. The Hook Road would have been the first stage of the planned urban motorway network for the city and this was to be its westernmost junction. The motorway would then have merged onto the A4160
Penarth Road. At a later stage this section of the Hook Road would have become the Southern Primary and it would have been extended west to Penarth.
This section of the route passes close to the city centre it would have been one of the busiest in the city. Two other junctions would have been built to the east of Butetown Interchange and their close proximity requires C/D roads and braiding to prevent any weaving. The mainline from the east feeds directly onto the roundabout with through traffic having to TOTSO so this suggests Butetown Interchange would have been an important access point to the city centre. A dual carriageway of D3 standard heading north from the roundabout would have carried this traffic.