The M6 northbound closes at J20 overnight on Thursday 17 September, and J20 and J21 shut on five nights this week. The 40mph contraflow starts on 12 October.
Work to replace the bridge joints on the M6 Thelwall Viaduct starts on Tuesday 1 September. National Highways puts the scheme at £27m and does not expect to finish until winter 2027-28.
The first day is quiet. Enabling works begin underneath the viaduct at Warrington Road, not on the motorway. The disruption arrives later in September, and the part that changes every Warrington journey on the M6 starts on 12 October.
From that date a 24/7 contraflow runs between junctions 20 and 21, with a 40mph speed restriction on both carriageways. It stays in place until winter 2027-28. All of this is set out on National Highways’ scheme page, updated on 19 August.
What the contraflow actually does
A contraflow moves traffic onto the opposite side of the road so the same number of lanes can be kept open while the closed side is worked on. Between junctions 20 and 21, until spring 2027, that means:
- By day: four lanes each way, 40mph on both carriageways. The southbound carriageway carries one of the northbound lanes.
- Between 10pm and 5am: four lanes stay open southbound, but the northbound carriageway is cut to a single lane.
- The northbound exit slip at junction 21 stays open at all times.
National Highways says this layout is the safest way to work while keeping the impact on journeys as low as possible, and that it significantly reduces the need for full motorway closures.
The overnight closures before then
Setting the layout up needs a run of closures first. Every one of these is 10pm to 5am:
- Monday 21 September: lanes 1 and 2, northbound.
- Tuesday 22 and Wednesday 23 September: lanes 1 and 2 northbound, including the exit and entry slip roads.
- Thursday 24 and Friday 25 September: lanes 1 and 2 southbound, including the exit and entry slip roads.
- Saturday 26 and Sunday 27 September: lanes 1 and 2, southbound.
- Monday 28 and Tuesday 29 September: full overnight closure, northbound.
- Wednesday 30 September and Thursday 1 October: full overnight closures, southbound.
- Friday 2 to Saturday 10 October: lanes 3 and 4 on both carriageways.
- Sunday 11 October: full overnight closure, northbound.
During the full closures the signed diversion is the M56, M60 and M62 in both directions. National Highways warns that closures can change at short notice and points drivers to its live travel updates before setting off.
What is actually shut this week, and why the scheme page will not tell you
National Highways’ scheme page still lists the contraflow and little else. Its own seven-day closure report says what is happening tonight. That report is a workbook republished twice a day on working days, one sheet per night, and the edition stamped 11 September 2026 at 15:32, covering Friday 11 to Thursday 17 September, has M6 work at junctions 20 and 21 on five of the seven nights:
| Night | What closes | Reason given |
|---|---|---|
| Fri 11 September, 11pm to 5am, and the J21 slip to 6am | M6 southbound J20 entry to the M56 links, the southbound J20 link to the M56 westbound, and the southbound J21 entry slip | Drainage |
| Mon 14 September, 9pm to 6am | M6 northbound J21 exit and entry slips | Drainage, J20 to J21 northbound |
| Tue 15 September, 9pm to 6am | M6 southbound J20 entry to the M56 links, and the southbound J20 link to the M56 westbound | Drainage |
| Wed 16 September, 9pm to 6am | The same two southbound J20 links, plus the southbound J21 entry slip | Drainage |
| Thu 17 September, 10pm to 6am | M6 northbound carriageway shut at J20, between the exit and entry slips, with the southbound J20 links and the southbound J21 entry slip shut from 9pm | Carriageway reconstruction and renewal, J20 to J21, both directions; drainage on the southbound slips |
| Sat 12 and Sun 13 September | Nothing at J20 or J21 | - |
The night to note is Thursday 17 September. That is a full carriageway closure of the M6 northbound at junction 20, not a slip road, and the reason given is carriageway reconstruction and renewal between junctions 20 and 21, which is the viaduct scheme’s own footprint. Everything else in the week is drainage on the southbound J20 links to the M56, which has now run on most working nights for a fortnight and will keep landing on the same slip roads through the two and a half years of the main job.
If you want to know what is shut tonight, read the closure report, not the scheme page. It is at nationalhighways.co.uk/roads-and-travel/live-travel-updates/road-closure-report/, it carries a “last updated” stamp at the top, and the sheets are one per night. The scheme page is a plan; the report is the schedule. The table above is the week of 11 to 17 September and will be out of date after that, which is exactly the point. One warning if you go looking yourself: the download link keeps the same address but the file behind it is swapped, so a cached copy can serve you a week-old workbook. Check the date on the front sheet before you trust it.
Why the joints are being replaced
The viaduct carries the M6 over the Manchester Ship Canal and the River Mersey. Bridge joints let the deck expand, contract and move as temperatures change, winds pick up or loads shift. National Highways says replacing them is essential to reduce the risk of unexpected closures, keep the bridge working safely and effectively, and minimise disruption for road users over the long term.
That last point is the trade. An unplanned closure of the Thelwall Viaduct empties onto Warrington’s own roads, which is why a problem on the M6 so often turns into queues on the A57 and A50.
The five stages
National Highways has published the scheme in stages, and warns that additional traffic management phases may be needed:
- Stage 1, September 2026: northbound contraflow set-up, plus scaffolding installation beneath the viaduct.
- Stage 2, mid-October 2026 to March 2027: joints replaced on the northbound side.
- Stage 3, spring 2027: the southbound contraflow goes in.
- Stage 4, spring to December 2027: joints replaced on the southbound side, then the contraflow comes out.
- Stage 5, winter 2027-28: resurfacing, road markings and road studs under overnight lane closures, with traffic sensors replaced under overnight full closures.
The agency adds the usual caveat: it aims to work to the programme, but unforeseen circumstances or bad weather may change it.
What it means for you
If you use the M6 between junctions 20 and 21, which covers Lymm, Grappenhall, Thelwall and Woolston, budget more time from 12 October and expect to be doing 40mph for well over a year. Four lanes each way in daylight means the layout is built to carry the traffic, but a lower limit across a long stretch still adds minutes to a commute, every day, for months.
The September nights are the sharper problem. Two of them, 28 and 29 September, close the whole northbound carriageway, and two more, 30 September and 1 October, close the whole southbound carriageway. If you drive that stretch after 10pm on those dates, the diversion is a long way round via the M56, M60 and M62.
Nothing here changes local roads directly. What it does change is the odds: a 40mph motorway lasting more than a year tends to push some drivers onto the A50 and A57 instead, and those are already the routes carrying the town’s other roadworks. Our Warrington roadworks and travel page tracks what is closed locally, and the train times page covers the alternative for longer trips.
Questions about the scheme go to National Highways on 0300 123 5000 or info@nationalhighways.co.uk. It posts North West updates as @HighwaysNWest.
Have your say