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We want to improve the junction 48 interchange.

Under construction
Region / County:
south west Wales
Start date:
spring 2021
End date:
winter 2021
approximately £3 million
First published:
2 March 2021
Last updated:


Why we are doing it

Junction 48 is the main junction for accessing Llanelli and Pontarddulais. 

Upgrading this junction will improve safety and reduce congestion. We will upgrade the existing path for cyclist and pedestrians.

    Current progress

    Works started in spring 2021.

    We have:

    • cleared the vegetation
    • built a slope on the A4138 and M4 westbound on-slip so we can widen the road and upgrade the existing footpath so that it can also be used by cyclists and other non-motorised vehicles
    • started the drainage works
    • started work on the new traffic signals and street lighting
    • put in the kerbs and pavements for the road
    • installed dormouse boxes
    • put in temporary windrows to connect vegetation during the works.

    Next steps

    Over the autumn and winter, we will:

    • landscape the roadsides by planting trees and plants to enhance the local environment for protected species
    • widen the road
    • build a combined footpath and cycle path
    • install infrastructure including sign foundations
    • install ducting for the street lighting system upgrade
    • install surface water drainage.

    What we are doing

    There are several issues with the layout of the A4138 and M4 junction 48 that contribute to congestion. They include:

    • limited opportunity for right turning traffic at A4138 to M4 eastbound on-slip. This impedes traffic heading towards Hendy
    • A4138 from Hendy layout with give way junction to traffic joining the M4 eastbound slip road
    • A4138/M4 westbound slip road layout peak times. The right turn lane junction relies on ‘goodwill’ of the A4138 traffic to exit the slip road at peak times
    • A4138 southbound from the M4 junction 48 towards Llanelli lane discipline is poor. The offside lane is not used as much as it could be
    • no provision for cyclists.

    We want to:

    • reduce congestion
    • reduce queuing during peak times
    • improve air quality
    • reduce driver frustration
    • improving safety.
    • improve connectivity
    • improve journey times
    • improve active travel through shared use path for cyclist and walkers
    • improve pedestrian and cyclists crossings.

    The proposed works will involve:

    • carriageway widening to increase efficiency of the A4138.
    • new traffic signals on the M4 westbound off-slip and Tal-y-Coed junctions
    • lane management measures on the A4138 southbound
    • improvements of all M4 junctions with the A4138
    • put in a combined footpath and cycle track that ties in a new route between the A4138 and Llangennech
    • environmental improvements for habitats such as dormice.


    Reports, environmental statements and plans

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