There is a Planned A48 Road Closure at Carmarthen for Six Weeks to repair a pipeline.
This is the main road West into, and East out of, Carmarthen so be prepared for severe delays on the alternate route.
See link for details and for planned alternate route.
http://www.carmarthenjournal.co.uk/carmarthen-to-nantycaws-a48-to-be-closed-for-six-weeks-for-pipeline-work/story-29436347-detail/story.html