M4 junctions 16 to 17 geotechnical and bridge works
We're undertaking a major £20 million improvement scheme on the M4 between junctions 16 and 17 near Swindon to maintain the long-term safety and reliability of this important route.
Latest updates
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04 September 2026
Planned closures and traffic management
During work, we'll reduce the motorway to two lanes with a contraflow system. We're setting a 50mph speed limit 24 hours a day to keep you and our workforce safe.
You may face minor delays while the contraflow is in place. Please allow extra time for your journey, especially at peak times. We'll provide 24/7 breakdown recovery throughout.
We'll need some overnight closures to safely install and switch traffic management layouts.
We'll clearly sign diversion routes via Wootton Bassett and Chippenham during closures.
Closures
5 October to 5 November - M4 east and westbound junctions 16 to 17
Overnight lane closures for vegetation clearance (8pm-6am).
M4 eastbound will also have a daytime hard shoulder closure.
12 to 13 November - M4 westbound junctions 16 to 17
Closed overnight (8pm-6am) to install two lanes running and 50mph speed limit.
M4 junction 16 to 17 closure and diversion route map
13 November 2026 to 17 February 2027 - M4 westbound junctions 16 to 17
We're closing the hard shoulder and lane 1, with a 50mph limit in place.
We're repairing
- the hard shoulder and drainage
- stabilising the embankment
- upgrading safety barriers.
Eastbound, all three lanes will run as normal.
Please remember that closures can change at short notice. You can find the latest information on our daily closures page or check for current incidents, disruptions and delays. Our travel alerts give details of high priority incidents on our network.
Project information
Overview
The work is starting on the 12 November 2026 and is expected to take two years to complete.
This is a significant investment in the M4 that will deliver vital repairs to maintain the safety, resilience and reliability of a key route across Wiltshire and the South West, while keeping traffic moving throughout most of the works.
Benefits
The most significant elements of the project are:
- stabilisation of a 600-metre section of embankment affected by ground movement which has led to the closure of the M4 hard shoulder in the area
- repairs to four bridge decks within the project area
- replace the safety barrier in the central reservation which has reached the end of its service life
The bridges carry the M4 over local roads, a farm access track and the railway line between Swindon and Bristol.
Train services on the railway will continue to operate and are not expected to be affected by the works.
Documents
Traffic information
Information about scheduled roadworks and events on our motorways and major roads.Sign up for updates!
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