Providing a signalised pedestrian crossing on the A484 between Trostre and Pemberton roundabouts will take about six weeks.
Work on the scheme, announced in December, was scheduled after the busy Christmas and New Year sales period at the popular trading estates to avoid the most disruption.
Whilst work is underway, it is necessary to narrow and reduce lanes approaching the works with traffic cones as a safety precaution.
Executive board member for transport and engineering, Cllr Colin Evans, said: “There has been a demand to improve the safety of pedestrians between Trostre and Pemberton, which have two of the busiest roundabouts in Carmarthenshire, for some years.”
He asked drivers to be more aware of the works, which had been well publicised, and to allow more time for their journeys when visiting or passing through the area.
Cllr Evans said: “It has been difficult for shoppers, pedestrians and mobility vehicles to navigate the area with the constant flow of traffic.
“Council officers worked hard to source the funds for the pedestrian and mobility scooter crossing.
“The project, costing approximately £60,000, is possible because of funding from the Welsh Government, under the Safe Routes in Communities Grant.
“The pedestrian controlled lights will make the crossing from Trostre to Pemberton safe and convenient by improving walking access to Coedcae School and for many shoppers and more than 3,000 employees across both sites.”
The work has to be completed by March 31 to meet funding criteria.
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