HS2 has completed a major engineering milestone near Birmingham after the second of two 320-metre viaducts was successfully launched across the M6 motorway, bringing a complex programme of bridge construction above one of Britain’s busiest roads to a close.
Engineers working for Balfour Beatty VINCI moved the final section of the 4,750-tonne west viaduct into position near Chelmsley Wood on Saturday 24 October, using hydraulic strand jacks to advance the steel structure across the motorway.
The operation took just nine hours, during which the deck travelled 76 metres into its final position, while traffic continued to use the M6 below.
The achievement means both M6 South viaducts are now structurally complete, marking further progress on the construction of HS2’s route into Birmingham.
Two 320-metre viaducts now span the M6
The parallel structures will carry HS2 trains in opposite directions, with the east deck accommodating services towards Old Oak Common and Euston in London, while the west deck will carry trains towards Birmingham Curzon Street.
The structures are also designed as part of the route intended to support services to destinations further north, including Manchester, Liverpool and Glasgow.
Both viaducts are constructed from weathering steel and supported by concrete piers, with just 100 millimetres separating the two decks.
Although each structure measures 320 metres, different construction sequences were required to accommodate the physical constraints of the site.
The east viaduct, completed in 2025, was launched in three stages, while the west deck required four incremental launches.
For each stage, additional steel sections were connected to the rear of the structure before hydraulic strand jacks pushed the assembled deck forward.
By the final launch, the steel structure was fully supported by concrete piers on either side of the motorway, enabling engineers to complete the movement without closing the M6 carriageways.
Raised embankments will subsequently be constructed on either side of the viaducts to connect them with the wider HS2 alignment.
Engineering approach minimises motorway disruption
The decision to assemble and launch the viaducts incrementally was driven by the challenge of constructing major railway infrastructure above an operational motorway.
Traditional construction approaches could have required extensive road closures, creating significant disruption for motorists and freight traffic.
Instead, the project team used a staged launching method that allowed most of the work to take place away from the live carriageway.
Ian Clarke, Senior Project Manager at HS2 Ltd, said: “These viaducts straddle some of the busiest sections of motorway in the country, which is why we adopt innovative techniques that allow construction to continue without closing the carriageway whenever we can.
“We have made great progress this year and I thank motorists and local communities for their patience.”
During the final operation, engineers advanced the west deck by 76 metres in nine hours, with HS2 reporting an average movement speed of 12 metres per hour during the launch.
Although the M6 remained open, the M42/M6 link road was closed to establish a safety exclusion zone around the works.
The road reopened at 9pm on Saturday 24 October, 25 hours earlier than scheduled.
Balfour Beatty VINCI completes complex bridge operation
The launch was delivered by HS2’s construction partner Balfour Beatty VINCI, which has been responsible for major civil engineering works along the route.
The project involved coordinating heavy steel construction, hydraulic launching systems and temporary safety arrangements within a constrained motorway environment.
Russell Luckhurst, the Balfour Beatty VINCI engineer leading the operation, said: “Two neighbouring viaducts that run parallel to each other now span the busy M6 motorway near Chelmsley Wood, after the west deck was safely and successfully moved into its final position over the weekend.
“It’s a huge moment for Balfour Beatty VINCI and HS2, concluding a major programme of work above the M6 – in extremely challenging weather conditions.”
The completion of both decks represents a significant structural milestone, although further work remains before the viaducts can accommodate railway systems and eventually carry trains.
The construction of adjoining embankments and the integration of the structures with the wider HS2 route will form part of subsequent activities.
Severe weather forces changes to M42 construction programme
While the M6 viaduct launch was completed successfully, strong winds over the weekend affected another element of HS2’s motorway construction programme.
Planned parapet installation works on the Water Orton viaduct above the M42 were postponed because of weather conditions.
The works have been rescheduled for the following weekend, with associated motorway closures planned from 9pm on Friday 30 October until 5am on Monday 2 November 2026.
The closures will affect the M42 northbound between junctions 6 and 9 and southbound between junctions 9 and 7.
The postponement highlights the operational challenges associated with delivering major infrastructure works at height, particularly where lifting operations and exposed structures are affected by strong winds.
Focus shifts to M42 triple-box structure in 2027
With the M6 South viaduct launches complete, HS2’s motorway construction programme will increasingly focus on further works around the M42.
A major element planned for 2027 is the triple-box structure near Coleshill, which will carry four HS2 railway tracks over the motorway.
HS2 is working with National Highways to agree the construction schedule and associated traffic management arrangements.
The structure will form another important part of the high-speed railway’s infrastructure in the West Midlands, where the route must cross existing strategic transport corridors.
The successful completion of the M6 viaduct launches demonstrates how complex bridge engineering techniques can reduce disruption during construction, while maintaining progress on major railway infrastructure.
For HS2 and its delivery partners, the milestone concludes one of the most challenging elements of construction above the M6 and allows attention to turn towards the remaining structures and connecting works needed to complete the railway alignment through the region.
