How about ploughing a road from St Athan up to the motorway. Rail and road link from an airport to the rest of the world.
Isn't that why they built that hangar big enough to hold a herd of white elephants? Shift flights to St Athan and then turn Rhoose Municipal aerodrome into "Penarth West Housing Estate". It does kinda look as if Cardiff is being run down whilst St Athan is being spun back up.