More than 180,000 vehicles cross the Thelwall Viaduct every day. The worn bridge expansion joints on both its northbound and southbound structures are being replaced in a £27 million scheme set to run until winter 2027/28.
From 12 October, a 24/7 contraflow with a 40mph speed limit comes into effect between junction 20 (Lymm) and junction 21 (Woolston) as National Highways steps up the work. The northbound carriageway shuts fully overnight on Sunday 11 October to allow installation of the contraflow system.
How the contraflow works
The contraflow arrangement lets traffic continue flowing while crews replace the bridge joints. During the day, northbound drivers use three lanes on their side plus one lane running southbound. Southbound traffic maintains four lanes on its own carriageway.
At night, between 10pm and 5am, the northbound side narrows to a single lane. The northbound exit slip road at junction 21 remains open throughout. The 40mph limit and narrow lanes stay in place for the duration, enforced by average speed cameras.
Why replace bridge expansion joints?
Expansion joints accommodate movement in the bridge deck caused by temperature changes, heavy vehicle loads, and wind pressure. They maintain a smooth surface for traffic across the structure.
National Highways states the existing joints on Thelwall Viaduct have reached the end of their operational lifespan. Renewal is essential to maintain safety, reduce the risk of unplanned closures, and limit disruption.
Project phases and timescale
The first phase targets the northbound joints, running until spring 2027. The contraflow then switches to the southbound side to allow completion there, with full project delivery expected by winter 2027/28.
The ongoing works follow enabling works under the bridge, which began on 1 September, and traffic management installation overnight between 28 September and 1 October.
Impact on M6 users
Drivers should anticipate a long-term 40mph speed limit and narrower lanes between junctions 20 and 21 for the next two years. Nighttime delays northbound are likely due to lane reductions.
Motorists travelling overnight on 11 October should check diversion routes in advance, as the northbound carriageway closes fully to allow contraflow installation.
Context within UK roads programme
This bridge joint replacement forms part of the third Road Investment Strategy (RIS3), covering 2026-2031, which allocates £8.4 billion toward carriageway resurfacing and bridge renewal across England’s strategic road network.
Thelwall Viaduct carries the M6 across the Manchester Ship Canal and River Mersey on two separate structures. Maintaining its integrity is critical for one of the busiest routes in the UK motorway network.
