Key points:
- National Highways is replacing the bridge joints on the M6 Thelwall Viaduct between J20 and J21.
- The £27 million project started in September 2026 and is due to finish in winter 2027/28.
- A 24/7 northbound contraflow with a 40mph limit has been in place since 19 October.
- Between 10pm and 5am, the northbound carriageway is reduced to one lane.
- Diversions for overnight closures run via the M56, M60 and M62.
What is being done and why
The Thelwall Viaduct carries the M6 over the Manchester Ship Canal and the River Mersey. According to National Highways, replacing the bridge joints is essential to reduce the risk of unexpected closures and keep the bridge working safely.
The works will run in five stages:
- September 2026: northbound contraflow set-up and scaffolding under the viaduct,
- mid-October 2026 to March 2027: joint replacement on the northbound side,
- spring 2027: southbound contraflow introduced,
- spring to December 2027: joint replacement on the southbound side, then removal of the contraflow,
- winter 2027/28: resurfacing, road markings, road studs and traffic sensors, using overnight full closures.
National Highways warns that extra traffic management phases may be needed and that the timetable could change because of weather or unforeseen problems.
Lane layout day and night
During the day, four lanes are kept open in each direction, with one northbound lane running on the southbound carriageway. A 40mph limit applies on both sides.
At night, between 10pm and 5am, the northbound carriageway is restricted to one lane. The J21 northbound exit slip road remains open during the first phase.
When the M6 is fully closed overnight, diversions run via the M56, M60 and M62 in both directions. National Highways publishes signed diversion maps for each carriageway.
Why it matters for hauliers
The Thelwall Viaduct lies on the M6 between the M56 interchange at J20 and the M62 corridor further north. That makes it part of the main road route for:
- freight between Scotland, Cumbria, Lancashire and the M56 towards North Wales and the port of Holyhead,
- traffic heading to and from the Liverpool City Region via the M62,
- north–south traffic avoiding the M60 around Manchester.
For operators running Irish Sea services via Holyhead, the works add another source of delay on a route already under pressure. The port’s empty £51m border post has also left drivers with few parking options near the terminal.
How to plan around the works
Night-time northbound runs are the most exposed, as only one lane is available between 10pm and 5am. Hauliers should check National Highways traffic information before departure, build extra time into schedules and allow for diversions when full closures are announced.
Drivers’ hours also need attention. A long hold-up on the viaduct can push a driver close to the limit before reaching a ferry or a delivery point. With the works due to last more than a year, the impact will be felt through two winters.
