The £500,000 scheme is needed to reduce the risk of flooding in the area which could result in lane closures.
Project sponsor, Chris Pope said:
We want to do everything we can to ensure this section of the M4 remains safe and reliable for many years to come and this investment in the drainage system will help us achieve that.
Work has been planned to minimise disruption but we would advise road users to allow extra time to complete their journeys.
The scheme, which will continue until the end of July, will require three narrow lanes to be put in place on three quarters of a mile on the westbound carriageway around junction 16 and a 50 mph temporary speed limit will be in operation for the safety of our workers and road users.
On occasions it will be necessary to close the westbound slip roads at junction 16 overnight and clearly signed diversion routes will be in place at these times. The first slip road closure is planned from 20:00 on Sunday 31 May.
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