A48 closes between Carmarthen and Nantycaws for repairs
The A48 in Carmarthenshire has closed for six weeks eastbound between Carmarthen and Nantycaws with concerns raised that it could cause "chaos".
The carriageway will be closed until 28 October for repairs on a defect in a stretch of pipeline which runs under the road from Pembroke refinery.
Mainline Pipelines Ltd said it would aim to reopen the road as soon as possible.
Llangunnor councillor Elwyn Williams has said residents faced "gridlock".
The old Nantycaws bypass will be used for diversions.
Mr Williams said: "It will be bumper to bumper, and it's going to be like that for as long as the dual carriageway is closed."
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Jenny Fox, from Carmarthen Chamber of Trade and Commerce, told BBC Radio Wales that Carmarthen looked congested ahead of the rush hour on Tuesday morning, with it looking like there were issues with some of the signalling.
She said: "There will obviously be an impact on businesses because we are one of the main route centres of west Wales.
"We realise that there's a huge dual carriageway that goes through, and a lot of people use it, from Ireland, from all over really, and we understand it is going to have an impact on the town."
Nantycaws resident Tristan Vetter described how the quiet village had been transformed into a "main road" during the works with a convoy of lorries heading through it.
"I haven't seen this much traffic down here for a long time," he said.
"It is getting very noisy."
Mr Vetter explained that a herd of cows cross the road twice a day from fields for milking, with locals stopping for around 20 minutes to let them cross.
It is unclear how this will affect traffic during the works.