Twin HS2 M6 South viaducts now structurally complete after final launch

HS2 has completed the installation of the final viaduct section over the M6 near Chelmsley Wood, marking the structural completion of both M6 South viaducts and closing a major phase of railway construction above one of the busiest motorway corridors in the country.

The milestone was achieved on Saturday 24 October with the launch of the west deck, a 4,750 tonne steel structure that was moved into its final position above the northbound and southbound M6 carriageways near junctions 4 and 4a. The operation was carried out by HS2's construction partner Balfour Beatty VINCI using hydraulic strand jacks while traffic continued to move beneath the bridge, limiting disruption to motorway users and demonstrating the level of planning and control required for construction over a live strategic route.

The west deck will carry trains towards Curzon Street Station in Birmingham city centre and onward to northern destinations including Manchester, Liverpool and Glasgow. The adjacent east deck, completed in 2025, will carry trains towards Old Oak Common and Euston in London. Together, the two parallel viaducts form a key element of the route's approach into Birmingham.

Each viaduct is 320m long and the two decks stand just 100mm apart. Both have been built in weathering steel and are supported by a series of concrete piers, with embankments to be formed on either side as the surrounding railway earthworks progress. Although identical in overall length, the two structures were assembled and launched in slightly different ways because of site constraints. The east deck was launched in three stages, while the west deck required four incremental launches.

The final launch of the west deck took nine hours to complete. During that period, the steel structure advanced 76m at an average speed of about 12m per hour. As with the earlier launches, additional steel sections were added at the rear and the deck was progressively pushed forward until the structure became fully supported on the concrete piers spanning the motorway corridor. This incremental launching approach enabled the final movement to be undertaken without a full closure of the M6 itself.

While the motorway remained open, the M42 to M6 link road was closed to create the necessary safety exclusion zone. That closure ended significantly earlier than planned, with the route reopening at 9pm on Saturday 24 October, 25 hours ahead of schedule. Ian Clarke, Senior Project Manager at HS2 Ltd, said innovative techniques were adopted wherever possible to allow construction to continue without closing the carriageway. Russell Luckhurst, the Balfour Beatty VINCI engineer leading the delivery of the work, described it as a huge moment concluding a major programme above the M6, carried out in extremely challenging weather conditions as strong winds affected large parts of the UK over the same weekend.

With both M6 South viaducts now structurally complete, the works in this area will move into the next stages, including the formation of the approach embankments and completion of associated railway infrastructure. The wider motorway-related construction programme will also continue, although some separate operations have already been affected by weather. Installation of parapets on the Water Orton viaduct over the M42 was postponed for safety reasons and has been rescheduled to the following weekend, with M42 junctions 6 to 9 northbound and 9 to 7 southbound closed from 9pm on Friday 30 October until 5am on Monday 2 November.

The completion of the M6 South viaducts represents more than just another structural milestone. It highlights the importance of launch construction methods in constrained transport corridors, where maintaining traffic flow is often as critical as the engineering execution itself. Building across a major motorway without widespread carriageway closures requires tight sequencing, temporary stability control, precise movement monitoring and close coordination between the rail project and highway authorities.

Attention will now increasingly turn to the next major motorway crossing activity on the route. In 2027, HS2's programme in this area is expected to focus on the triple box structure near Coleshill, which will carry four railway tracks over the M42, with HS2 working closely with National Highways to agree the schedule of works. That next stage will continue the broader effort to thread the high speed route through one of the most infrastructure-dense sections of the West Midlands.

For the M6 South crossing, however, the central structural challenge has now been overcome. With the final west deck in place beside the already completed east deck, HS2 has completed one of its most prominent motorway viaduct operations in the Birmingham section of the route.

The following video was taken right before the final viaduct installation.