HS2 Launches 175-Beam Roof Installation for M42 Twin Box

SOLIHULL, UK – Engineers for HS2’s main works contractor Balfour Beatty VINCI (BBV) will begin lifting 175 roof beams onto the M42 twin box structure starting the first of four weekend motorway closures in June. The 300-metre-long twin box, located less than a mile from the future Interchange Station, will carry four HS2 railway tracks above the carriageway while vehicles drive through its lower section.

What Is the Full Scope of This Project?

The twin box structure rises on 46 supporting columns and two 10-metre-high walls built from prefabricated hollow blocks weighing an average of 14 tonnes each. The walls and columns, assembled using a Design for Manufacture and Assembly (DfMA) approach, now support the forthcoming 9,800-tonne beamed roof. Over four weekends in June, July, August and September, a 300-tonne crawler crane will place 175 beams—each 23 metres long and weighing 56–92 tonnes—bridging the gap between the walls and the central pier. The modular construction has eliminated the need for long-term motorway closures, with the work constrained to temporary weekend shutdowns agreed with National Highways.

Key Project Data

How Does This Compare to Similar Projects?

While the twin box is a 300-metre road-under-rail modular bridge, the world’s largest dual road/rail crossing under construction uses a different approach on a vastly larger scale. The 18-kilometre Fehmarn Belt immersed tunnel linking Denmark and Germany will carry both road and rail in separate concrete tubes. Its prefabricated elements weigh up to 73,000 tonnes each—over 5,200 times the mass of a single twin box wall block—and are produced in dedicated factory facilities before immersion in a dredged trench. Both projects rely on extensive off-site manufacture to minimise disruption, but the Fehmarn tunnel’s 73,000-tonne segments represent an entirely different order of magnitude from the twin box’s 92-tonne roof beams (Source: MarineLink, 2025).

Editor’s Analysis

The M42 twin box exemplifies how HS2 is deploying modular, DfMA methods to shrink motorway occupation from months to a handful of weekends—a pattern likely to be replicated on other UK infrastructure schemes. That approach feeds directly into a broader investment environment in which railway electrification and capacity expansion are projected to generate 250,000 additional UK jobs by 2050 (Source: edie.net, 2025). With the twin box forming part of the same HS2 corridor, the structure’s fast-track assembly reinforces the operational logic of building high-capacity, electrified lines while keeping existing road networks open.

FAQ

Q: How will traffic be affected during the M42 closures?
A: The M42 northbound will close between Junctions 5a and 9 on four separate weekends in June, July, August and September. Traffic will be diverted via the A4545, A45, A452 and A446 before rejoining at M42 Junction 9. Southbound closures will also be in place; National Highways advises using signed diversion routes and allowing extra journey time.

Q: How many beams are being installed and what is their weight?
A: A total of 175 roof beams will be lifted. Each beam is 23 metres long and weighs between 56 and 92 tonnes, requiring a 300-tonne crawler crane for installation.

Q: When is the entire twin box expected to be operational?
A: No official completion date for the full twin box has been disclosed. The roof installation phase finishes by September 2025, and the structure will ultimately support HS2’s Phase One tracks, which are currently targeted to open between 2029 and 2033.