M4 junction 17 could see more lanes added under new plans

Wiltshire Council has plans to further redevelop the layout at junction 17 of the M4, near Chippenham, following previous works in 2018 and alterations made by St Modwen Logistics last year.

The latest plans would see traffic lights introduced at all approaches to the roundabout while the carriageway would be widened at all approaches, providing increased traffic capacity.

This would include additional lanes on the A350, the A429, the M4 off slips, and the B4122.

There would also be an increase in the number of lanes across the motorway bridges, from two to three, and the layby along the A429 would be repositioned to allow for carriageway widening work.

The scheme had initially been scheduled for completion in 2026 following work beginning in the spring of 2025.

The approach to junction 17 of the M4 from the A350 (Image: Newsquest)

But Wiltshire Council says it now plans to start work on the junction in 2026 after delays to the project.

The council is still awaiting approval from the Department for Transport after submitting their Outline Business Case for the proposal.

It was initially hoped that approval would be granted in October 2022, but an updated copy was sent in the summer of 2023 and no decision on funding has yet been made.

Cllr Caroline Thomas, the cabinet member for transport, said: “Following the submission of an Outline Business Case for the M4, Junction 17 Major Road Network (MRN) scheme, we are awaiting a decision from the Department for Transport.

“If our submission is successful, and funding is obtained, we will be able to move on to the design stage, including the development of a Full Business Case for the scheme.

“At this stage, it is hoped that we will be in a position to work towards construction of the scheme starting in 2026, however, the timeline is dependent upon funding confirmation from the DfT.”

Traffic on the approach to the M4 junction 17 (Image: Newsquest)

Motorists have already faced major changes at the busy junction in the last 12 months.

A change of the layout means all drivers approaching on the A350 from Chippenham must stay in the right-hand lane unless they are turning onto the M4 heading west.

This change has sparked confusion and anger amongst some drivers who labelled the roundabout an “accident waiting to happen.”

The council hopes the latest plans will maximise and optimise the capacity of the junction to allow for expected future traffic growth.