Engineers working on HS2 have set a new benchmark for UK infrastructure delivery after successfully sliding a colossal 4,600-tonne viaduct across the M6 without closing the motorway – dramatically reducing disruption for drivers and showcasing cutting-edge engineering.
The 17-hour operation marked the final stage in a three-phase process to assemble and position the 315-metre East deck of the M6 South viaduct. This structure will eventually carry high-speed trains to Birmingham and beyond, forming a critical link in Britain’s new rail network.
While an earlier slide required a full weekend closure of the motorway, HS2’s main works contractor Balfour Beatty VINCI (BBV) worked hand-in-hand with National Highways to pioneer a ‘fully restrained’ sliding technique. This innovation allowed the team to move the viaduct safely over live traffic – a first for UK motorways.
To prepare, the M6 was closed overnight between Junctions 4 and 5 on Thursday 11 December, enabling engineers to shift the viaduct forward by 12 metres so both ends rested securely on concrete piers. On Saturday, the structure was then pushed across the motorway at a controlled speed of 13 metres per hour, with only the M42 slip road closed during the weekend.
This milestone means the M6 South viaduct project has reached its halfway point. Over the next year, the same technique will be used to position the parallel West deck, which will carry southbound trains.
Caroline Warrington, HS2 Ltd’s Head of Delivery, said:
“Along the HS2 route we are pioneering new approaches to engineering and construction in order to deliver more efficiently and with less impact on our neighbours.
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 achievement comes as HS2 Chief Executive Mark Wild leads a comprehensive reset of the programme, focused on efficiency and cost control. Over the past year, HS2 has prioritised productivity gains across its construction sites.
The viaduct’s design reflects this drive for efficiency. Each section is assembled off to one side before being launched over the motorway, reducing disruption for road users. For the latest phase, engineers used strand jacks to winch the structure forward, sliding it across non-stick pads made from a material more commonly found on frying pans.
Russell Luckhurst, BBV’s lead engineer on the works, said:
“We’re all feeling a huge sense of pride after sliding a 4,600-tonne viaduct into its final position this weekend. The third and final slide of the East deck viaduct was delivered over a live motorway for the first time in the UK, making this achievement even more special.
Using this ‘fully restrained’ technique meant we were able to keep disruption to an absolute minimum. Our focus will now turn towards the neighbouring West deck viaduct, which will be launched in multiple phases throughout 2026, as well as the East deck finishing works.”
The viaduct comprises a hollow double-box structure made from weathering steel, which forms a natural protective layer and eliminates the need for repainting. Four pairs of concrete piers support the decks, the tallest standing at 9.9 metres. A 4.5-metre-high parapet will be installed on the Chelmsley Wood side to reduce noise for local residents.
To minimise future road closures, the viaduct was launched with 82 precast slabs already in place. The structural design was delivered by BBV’s Design Joint Venture (DJV), which includes Mott MacDonald, SYSTRA, and WW+P Architects.
Victoria Lazenby, National Highways Regional Director for the Midlands, said:
“Our key focus is the impact that these major construction works have on our roads – we must both ensure the safety of road users and minimise the disruption they face.
So we are delighted that this innovative technique has meant that not only was this enormous structure slid into place without having to close the motorway during the day but also that the total number of closures needed has also been halved.
We will continue to work with HS2 and their partners to ensure the smooth running of our roads while this huge infrastructure project takes place and support any initiatives which will reduce disruption for drivers and local communities.”
Images and video credit: HS2
