May I ask those resident in Wales to give a comparative numerical estimated daily usage of:-
A)...A black route M4 south of Newport
B)...A reopened Carmarthen to Aberystwyth Railway.
You miss the point Paul the projects are not about "numbers".
The current Welsh Labour (Welsh Government) see it as a grand project to boost the economy of Wales and relieve traffic congestion (and the moaning that goes with it) around the Brynglas Tunnels near Newport. it also "rewards" Labour voting areas with investment projects.
Plaid see the M4 Relief Road as a Labour spending all the transport budget in one small corner of South Wales Coastal plain Wales favored by the Cardiff "elite" and is yet further evidence of the bias against the rest of Wales.
In a economy already saturated with Motor Vehicle usage adding some extra road capacity in one small part of it is not going to have any transformational affect as it will not result in any step change in provision. As they say we can now drive to the next traffic jam quicker. The road if built will just create new traffic that creates new jams elsewhere either side of it and any overall benefit to the areas economy will be lost and maybe even head the other way. Theirs also the environmental impact and the affordability/opportunity cost to consider. Plus all that extra Nitrogen Dioxide for the good voters of the Cardiff and Newport suburbs to choke to death on.
Whatever you view on the AYW to CMN reopening it wont have the negative impact on the environment, health and road congestion that the M4 Relief Road will nor the same opportunity cost.
However in my opinion the South Wales Metro should be the priority transport project per se in Wales as if done properly it will deliver a step change in provision for the million or so people that live in the Cardiff City Region.
Other Metropolitan areas with populations of One million plus in the UK that need this approach are Glasgow/Edinburgh, Newcastle/Sunderland, Leeds/Bradford, Sheffield, Greater Manchester, Merseyside, West Midlands, Derby/Nottingham/Leicester, Bristol and South Hampshire.