HS2 engineers are preparing to install the roof structure of a major ‘twin box’ crossing over the M42 near Solihull, marking a significant milestone in the delivery of the high-speed railway across the Midlands motorway network.
The 300-metre-long structure, located less than a mile from the future HS2 Interchange Station, will eventually carry four railway tracks above live traffic, with vehicles passing through twin concrete boxes beneath.
With the two 10-metre-high supporting walls now complete and a central pier of 46 columns nearing completion, the project team—led by Balfour Beatty VINCI (BBV)—is moving into the next phase: installing 175 prefabricated roof beams over four weekend possessions between June and September.
Modular construction driving efficiency
The twin box has been delivered using a Design for Manufacture and Assembly (DfMA) approach, integrating large prefabricated components to minimise disruption on one of the region’s busiest strategic routes.
Each hollow concrete wall block, weighing an average of 14 tonnes, has been lifted into place and infilled with reinforced concrete—creating the structural capacity required to support a 9,800-tonne roof.
The next stage will see beams ranging from 56 to 92 tonnes, and measuring 23 metres in length, craned into position using a 300-tonne crawler crane.
Planned closures to enable complex installation
Due to the scale and complexity of the operation, installation can only take place during temporary motorway closures. The works have been carefully scheduled with National Highways to reduce disruption, with teams aiming to complete installations during weekend possessions and reopen the motorway by early Monday morning.
Approximately 44 beams will be installed during each closure, with around 180 engineers and specialists working in shifts around the clock to maintain progress.
Strategic importance within HS2 delivery
The M42 twin box is one of three major motorway-crossing structures under construction across the Midlands this year, alongside the Water Orton twin viaducts and the M6 South viaduct.
The scheme is being delivered with strong UK supply chain involvement. Expanded Structures—specialists in modular bridge systems—are leading the design and installation, while Explore Manufacturing is producing precast components at its Worksop facility.
Industry leadership reaction
Agnes Usciak, HS2 Ltd’s Senior Project Manager for the works, said:
“This is a huge moment for the project, and a clear sign of the progress we are making as we begin bridging the gaps over the region’s motorway network.
“This is British engineering at its very best, and it’s fantastic that a UK-based firm has led the way in developing this innovative design solution for the twin box, with manufacturing taking place in the midlands.”
Oliver Shore, Project Director at Balfour Beatty VINCI added:
“This ambitious structure, spanning a busy stretch of the M42 motorway near Solihull, is a huge engineering challenge which has required precision planning and close collaboration with many stakeholders.
“Now the supporting walls are complete, we’re getting ready to move to the next exciting phase of construction, which is the installation of the roof over four weekend carriageway closures throughout the summer.”
Expanded Structures, which previously delivered HS2’s first permanent structure on the M42 and is involved in Old Oak Common station works, emphasised the benefits of off-site manufacturing.
Tim Rowe, Project Leader at Expanded said:
“Throughout the planning for this project it was an underlining principle that that there would be minimal disruption to road users. Our modular bridge solution offers a quicker and safer installation to that of traditional bridge construction, leveraging the benefits of off-site manufacture to take risk and disruption away from the site and public interfaces.
“Whilst the bridge is already an impressive structure we have been looking forward to this moment, installing the beams and connecting all the individual elements in one continuous structure.”
Managing disruption on a live motorway
National Highways has supported planning and community engagement, ensuring drivers, residents and businesses are informed of diversion routes and closure schedules.
Image and Video credits: HS2
