The M4 in South Wales is currently being widened in both directions between junctions 29 and 32, around Cardiff. This entails narrowing the road by one lane on both sides, so when there is a high volume of traffic it can be VERY slow going. An alternative route is to drive through Cardiff on the A48 dual carriageway which is surprisingly quick going, generally. The procedure is:
(1) Consult traffic news - if the M4 is moving fairly freely then it is probably best to stay on it and ignore this diversion.
(2) Leave the M4 at junction 28 and join the A48 or at junction 29 and join the A48(M).
(3) Follow the A48 into northern Cardiff.
(4) Keep on following the A48 until you pass a large retail park on the left, with a Staples, Wicks and a massive Tesco Extra.
(5) Get into the left hand lane as you pass Tesco.
(6) Bear left off the A48 towards the A4119.
(7) Turn right at the T junction onto the A4119 for Llantrisant.
(8) Follow the A4119 up past Llandaff, towards Radyr, on over the M4 and up through Groes-Faen.
(9) At the T junction turn left for the M4.
(10) Take the third exit on the roundabout to rejoin the M4 at junction 34, heading westwards towards Port Talbot and Swansea.
I’ve done this route several times recently and, apart from being a little slow getting past Tesco on a Saturday morning (!), it’s always been fairly quick and smooth.
