 The GB £ 14 @.@ 5 million Capel Llanilltern – Culverhouse Cross Link Road ( Welsh : Ffordd Gyswllt Capel Llanilltern – <unk> <unk> ) , also known as the A4232 Trunk Road ( as it is the only section of the PDR which is a trunk road ) , between the Capel Llanilltern Interchange ( 51 @.@ <unk> ° N 3 @.@ <unk> ° W ﻿ / 51 @.@ <unk> ; <unk> ﻿ ( Capel Llanilltern Interchange ( M4 <unk> ) ) ) and the Culverhouse Cross Interchange ( 51 @.@ <unk> ° N 3 @.@ <unk> ° W ﻿ / 51 @.@ <unk> ; <unk> ﻿ ( Culverhouse Cross Interchange ) ) was opened in 1985 . It was designed to provide a by @-@ pass for traffic from the M4 to the Vale of Glamorgan . It is 5 @.@ 47 km ( 3 @.@ 40 mi ) in length and includes the Ely Viaduct close to <unk> @-@ super @-@ Ely . The trunk road is maintained by the South Wales Trunk Road Agency ( <unk> ) on behalf of the Welsh Assembly Government ( WAG ) . The remainder of the PDR is a primary route , which is maintained by Cardiff Council . In 2006 variable message signs were installed on the Capel Llanilltern – Culverhouse Cross Link Road by <unk> Systems to display messages giving motorists warning of road and weather conditions , accidents , congestion and major events held in the area . 
