 The Pentwyn Link Road ( Welsh : Ffordd Gyswllt Pentwyn ) , which is also known as the North Pentwyn Link Road , runs from the Pontprennau Interchange ( 51 @.@ 528660 ° N 3 @.@ 130240 ° W ﻿ / 51 @.@ 528660 ; -3.130240 ﻿ ( Pontrennau Interchange ) ) on the A48 and the Pentwyn Interchange ( 51 @.@ 541525 ° N 3 @.@ 128749 ° W ﻿ / 51 @.@ 541525 ; -3.128749 ﻿ ( Pentwyn Interchange ( M4 J30 ) ) ) on the M4 ( junction 30 ) . It is 1 @.@ 61 km ( 1 @.@ 00 mi ) in length and was opened by John Redwood MP , the Secretary of State for Wales on 20 June , 1994 . It provides a link between the Eastern Avenue ( A48 ) and the M4 so that westbound traffic from the east of the city can get onto the M4 without having to go through the city , via the A48 and A470 . In addition it also provides access to the community of Pontprennau to the national road network . This link was financed by private developers as part of a large scale housing development at Pontprennau . 
