Drivers on the M6 near Birmingham kept moving at junction 4/4a while engineers pushed the last section of a 4,750-tonne HS2 viaduct 76 metres across the motorway in nine hours, at an average of 12 metres per hour, without closing the carriageway.
The operation took place on Saturday, 24 October 2026, near Chelmsley Wood in the West Midlands. HS2 Ltd, the company building Britain’s new high-speed railway, announced the result on 26 October.
With it, both M6 South viaducts are now structurally complete. The pair of steel decks will carry high-speed trains over one of the busiest stretches of motorway in the country.
Giant jacks pushed the deck while cars passed underneath
The final section of the 4,750-tonne structure was launched above the northbound and southbound carriageways using giant hydraulic jacks, while vehicles travelled below, according to HS2.
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The method is called incremental launching. For each launch, new steel sections are added to the rear of the structure, and the whole deck is pushed forward using strand jacks, a little at a time.
By the final launch, the weight of the steel deck was fully supported on concrete piers at either side of the carriageway. That is what allowed the “last push” to happen safely while traffic kept flowing.
Nine hours to move 76 metres
It took engineers from Balfour Beatty VINCI, HS2’s construction partner, just nine hours to complete the final launch of the west deck. In that time the steel deck moved forward 76 metres.
That works out to an average speed of 12 metres per hour, far slower than a person walking. Those 76 metres are close to a quarter of the full 320-metre length of the HS2 viaduct.
Russell Luckhurst, the Balfour Beatty VINCI engineer leading the work, said the west deck was “safely and successfully moved into its final position over the weekend.”
Two decks of 320 metres, only 100 millimetres apart
The M6 South crossing is actually two viaducts side by side. Both are 320 metres long, and the parallel structures stand just 100 millimetres apart, according to HS2.
They were built using weathering steel, the rust-coloured material that forms its own protective layer, and they rest on a series of concrete piers. Raised embankments will later be formed on either side.
Because of site constraints, the two decks were launched in slightly different ways. The west deck went across in four incremental stages, and the east deck in three.
Counting both decks, that is seven separate launches to put 640 metres of steel deck over the M6, with the very last push on 24 October carried out while traffic on the motorway kept moving in both directions below.
One deck goes to London, the other to Birmingham
The east deck was completed in 2025. It will carry high-speed trains towards HS2’s two London stations, Old Oak Common and Euston.
The west deck, the one moved into place on 24 October, will carry trains towards Curzon Street Station in Birmingham city centre, and to destinations further north, including Manchester, Liverpool and Glasgow.
In practice, the two decks split the traffic by direction. Trains heading to the capital will use one of them, and trains heading to Birmingham and the north will use the other, side by side over the same motorway.
The link road reopened 25 hours early
The M6 stayed open to traffic throughout the weekend. Only the M42 to M6 link road was closed, to create a safety exclusion zone around the work.
That link road reopened 25 hours ahead of schedule, at 9 pm on Saturday, 24 October, according to HS2. For drivers in the area, it meant the closure ended on the same evening the deck arrived.
“These viaducts straddle some of the busiest sections of motorway in the country,” said Ian Clarke, senior project manager at HS2 Ltd. “We adopt innovative techniques that allow construction to continue without closing the carriageway whenever we can.”
Strong winds forced another job to wait
Not everything went to plan that weekend. Strong winds hit large parts of the UK, and parapet installation on the Water Orton viaduct, above the M42, was postponed for safety reasons.
That work has been moved to the following weekend. The M6 will be closed between junctions 6 and 9 northbound and 9 and 7 southbound from 9 pm on Friday, 30 October, to 5 am on Monday, 2 November.
HS2 also released timelapse footage of the launch, which the company describes as a highly skilled engineering operation carried out above live traffic.
Luckhurst noted that the M6 South work was completed “in extremely challenging weather conditions.” Clarke said the project had “made great progress this year” and thanked “motorists and local communities for their patience.”
A huge moment for the builders
For the construction team, the weekend closed a long chapter. “Two neighbouring viaducts that run parallel to each other now span the busy M6 motorway near Chelmsley Wood,” Luckhurst said.
“It’s a huge moment for Balfour Beatty VINCI and HS2, concluding a major programme of work above the M6,” he added. The steel is in place; what remains is the work around it.
Next up, a triple box over the M42
HS2’s motorway work is not finished. In 2027, the programme will centre on the so-called triple box, a rail-over-road structure that will carry four HS2 railway tracks over the M42 near Coleshill.
HS2 says it is working closely with National Highways to agree the schedule of that work. For drivers in the West Midlands, that means more motorway engineering still to come, as the HS2 announcement makes clear.
Would you rather drive under a 4,750-tonne viaduct being pushed over the M6, or sit through a full motorway closure?
