People wanting to travel to Cardiff from Barry currently have 3 options: 1 Sully and Penarth 2 Dinas Powys 3 Wenvoe
These ultimately branch into 4 routes as they enter Cardiff
1 Culverhouse Cross 2 Leckwith 3 Penarth Rd 4 International Sports Village.
The Wenvoe and Dinas Powys routes are terribly congested at peak times. A DP bypass may be built but the congestion would merely be shifted to between the Merrie Harrier and Barons Court junctions, although this would spare the poor people of Dinas Powys from being choked by fumes.
There is no easy solution to the difficulty of commuting from Barry to Cardiff by car, or in making Barry more accessible to Cardiffians using their cars. I think that the Metro may have plans to increase service from 4tph to 5tph on the VOG line and that, combined with more capacious trains, will help a little.
As for the link from Barry to the M4, Five Mile Lane, it is in the process of being significantly upgraded.
http://www.valeofglamorgan.gov.uk/en/ou ... oject.aspx