Engineers delivering HS2 have completed a landmark operation to slide a 4,600-tonne viaduct across the M6 without closing the motorway, marking what is believed to be a UK-first and significantly reducing disruption for drivers.
The 17-hour operation saw the final stage of a three-phase push to install the 315-metre east deck of the M6 South viaduct, which will carry high-speed trains towards Birmingham and the North. Unlike earlier stages, the final slide was completed over live traffic using a newly developed ‘fully restrained’ technique.
Led by HS2’s main works contractor, Balfour Beatty VINCI (BBV), the team worked closely with National Highways to design a process that kept the motorway open. Only the M42 slip road was closed during the weekend works.
Ahead of the main slide, the M6 was closed overnight between junctions 4 and 5 on Thursday 11 December to move the structure forward by 12 metres, ensuring both ends were fully supported on concrete piers. On Saturday, the viaduct was pushed into its final position at a rate of around 13 metres per hour.
The successful move brings construction of the M6 South viaduct to its halfway point. A parallel west deck will be assembled and launched using the same method during 2026 to carry southbound services.
Caroline Warrington, HS2 Ltd’s head of delivery, said the operation demonstrated how innovation can reduce the impact of major construction works:
“We believe this fully restrained slide was a first for the country, but most importantly it means we’ve been able to cut in half the number of times we’ve had to close the motorway. I’d like to thank everyone who worked so hard to make the operation a success.”
The viaduct has been designed to minimise disruption, with sections assembled beside the motorway before being slid into place. Strand jacks were used to move the structure across low-friction pads, using a non-stick material similar to that found on household cookware.
Russell Luckhurst, BBV engineer leading the works, said the team was proud to complete the final slide over a live motorway:
“Delivering the third and final slide of the east deck without closing the M6 during the day is a huge achievement. Our focus now turns to launching the west deck and completing finishing works on the east deck.”
Each viaduct consists of a hollow double-box structure made from weathering steel, chosen for its durability and reduced maintenance needs. The decks are supported by four pairs of concrete piers, with the tallest standing nearly 10 metres high, and will include a 4.5-metre noise barrier facing Chelmsley Wood.
Victoria Lazenby, regional director for National Highways in the Midlands, said the approach struck the right balance between safety and disruption:
“This innovative technique meant the structure could be slid into place without daytime motorway closures and with fewer total closures overall. We’re pleased to support initiatives like this that reduce the impact on road users and local communities.”
The operation forms part of HS2’s wider push to improve productivity and efficiency as the programme undergoes a comprehensive reset to deliver the railway at the lowest reasonable cost.
