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The HS2 M6 viaducts are now structurally complete, after engineers slid the final section of the second viaduct into place above one of England’s busiest motorways while traffic kept moving underneath. According to SYSTRA UK, the milestone was reached on Saturday, October 24, 2026, near Chelmsley Wood in the West Midlands, when the west deck of the M6 South viaducts was launched over the M6 at junction 4/4a.
HS2 M6 viaducts: what happened above the M6
The final launch moved the west deck forward by 76 metres in nine hours, according to HS2 Ltd. The company says the steel deck travelled at an average speed of 12 metres per hour, and the M6 stayed open to traffic throughout the weekend operation. Only the M42 M6 link road was closed, to provide a safety exclusion zone, and HS2 Ltd says it reopened 25 hours ahead of schedule, at 9pm on Saturday, October 24. With that move, both of the parallel HS2 M6 viaducts are structurally complete. According to SYSTRA UK, each viaduct is 320 metres long, the two structures stand just 100 millimetres apart, and both are built from weathering steel supported on concrete piers. The east deck was completed in 2025, while the west deck needed a fourth launch stage to reach its final position.
How engineers launched a 4,750 tonne deck over live traffic
The engineering challenge was to move an enormous steel structure across a live motorway without closing it. According to SYSTRA UK, the final section of the 4,750 tonne west deck was launched above the northbound and southbound carriageways using giant hydraulic jacks while vehicles travelled below. The method is known as incremental launching. Additional steel sections are added to the rear of the deck, and the whole structure is propelled forward in stages using strand jacks. According to SYSTRA UK, by the final launch the weight of the steel deck is fully supported on concrete piers at either side of the carriageway, which means the last push can be executed safely while traffic flows underneath. The west deck was harder to build than its neighbour. According to reporting on the project, tight space, the staggered positions of the abutments, and the curve of a nearby loop road left a shorter launch platform, so the west deck was built in four smaller sections before sliding into place. The east deck, by comparison, was launched in three stages, weighed 4,600 tonnes, and reached its final position in December 2025. The structural design was delivered by Balfour Beatty VINCI’s Design Joint Venture, made up of Mott MacDonald and SYSTRA, with Weston Williamson and Partners, according to SYSTRA UK.
Why the HS2 M6 viaducts matter
The completion matters because it removes one of the riskiest interfaces on the HS2 route: the point where a new high speed railway must cross a strategic motorway. Closing the M6 for such a launch would have caused major disruption across the West Midlands, so launching over live traffic protected both the construction programme and the road network. HS2 Ltd senior project manager Ian Clarke said the team adopts innovative techniques that allow construction to continue without closing the carriageway whenever possible, and thanked motorists and local communities for their patience. The two decks also serve different directions, which shows how much of the future railway depends on this one crossing. According to SYSTRA UK, the east deck will carry high speed trains towards HS2’s London stations, Old Oak Common and Euston, while the west deck will carry trains towards Curzon Street station in Birmingham city centre and destinations in the north, including Manchester, Liverpool and Glasgow.
What happens next on HS2 in the West Midlands
Structural completion is not the end of the work at this location. According to SYSTRA UK, raised embankments will be formed on either side of the viaducts. Strong winds during the same weekend also forced a postponement of Water Orton viaduct parapet installation works above the M42, for safety reasons, and HS2 Ltd says that work is rescheduled for the weekend of October 30 to November 2, 2026, with closures on the M42 between junctions 6 to 9 northbound and junctions 9 to 7 southbound. Looking ahead to 2027, according to HS2 Ltd, the motorway construction programme will centre on the triple box, a rail over road structure that will carry four HS2 railway tracks over the M42 near Coleshill. HS2 Ltd says it is working closely with National Highways to agree the schedule for that work. The wider opening stage of HS2, between Old Oak Common in London and Birmingham Curzon Street, was expected between May 2036 and October 2039, according to a May 2026 update from the Department for Transport reported in project coverage.
Source: SYSTRA UK, “HS2 installs final viaduct over M6”, October 26, 2026, and HS2 Ltd via Building, Design and Construction Magazine.