National Highways, the government-owned company responsible for England’s motorways and major A roads, has selected the company that will build the tunnel boring machine (TBM) for the Lower Thames Crossing, moving the project a step closer to construction.
The machine will be built in Germany by Herrenknecht, which has previously built TBMs for London’s Elizabeth Line, the Silvertown Tunnel, HS2 and the Thames Tideway tunnels. It will be bought and operated by Bouygues Travaux Publics Murphy Joint Venture, the project’s delivery partner.
Largest tunnelling machine in Europe
At 16.4 metres in diameter, the TBM will be the largest ever used in Europe and the third largest in the world. It will be 120 metres long and weigh more than 5,000 tonnes, meaning it must be delivered to site in segments by sea, carried up the Thames and landed at the Port of Tilbury.
The machine is due to be delivered and start work in 2028. It will dig two parallel tunnels, each more than twice the size of the existing tunnels at Dartford and large enough for three lanes of traffic at 70mph. A single machine will dig both tunnels, being turned around after completing the first, to save cost and reduce the project’s carbon footprint.
It is a variable-density machine, designed to dig through the water table and varying ground conditions, including clay and chalk up to 60 metres below the Thames, and will be powered by electricity from renewable sources.
Tackling congestion at Dartford
The Lower Thames Crossing is intended to double road capacity across the Thames east of London, addressing congestion at the existing Dartford crossing and creating a new trade route linking ports in the South East with the Midlands and the North.
The tunnel will run for 2.6 miles, making it the UK’s longest road tunnel, as part of a wider 14.3-mile route of which around 80% will be in tunnel, cutting or behind an embankment. National Highways says a tunnel was chosen over a bridge to avoid affecting local communities and protected wetland bird habitats.
Construction on the wider project began earlier this year, with the new road expected to open in the early-to-mid 2030s. National Highways says innovations including low-carbon concrete tunnel linings and a design that reduces the amount of material used are intended to make the crossing the first major UK infrastructure project to be carbon neutral in construction.
Industry reaction
“We are working at pace and are on track to deliver Britain’s greenest road, driving down carbon emissions and protecting the environment as we do so,” says Shaun Pidcock, delivery director for the Lower Thames Crossing. “Choosing our partner to supply the giant tunnel boring machine means real progress on the project – and we’ll put it to work as soon as it arrives on site in 2028.”
According to Didier Jacques, tunnel construction director at Bouygues Travaux Publics Murphy Joint Venture, the team will now move on to detailed design development of the TBM in close collaboration with Herrenknecht, with a continued focus on reducing carbon emissions, pioneering innovative solutions and embedding safety at every stage of construction.
Frédéric Battistoni, head of project management at Herrenknecht, says the machine will be the largest ever built at the company’s German headquarters, and the largest variable-density TBM it has produced, featuring the largest accessible cutting wheel the company has built. He adds that it has been designed to adapt to changing ground conditions while enhancing safety, efficiency and logistics during tunnelling, and will support excavation of both tunnel drives through a planned U-turn configuration.
The Lower Thames Crossing was granted a Development Consent Order by the Secretary of State for Transport in March 2025, with the government allocating the final part of public funding in the November 2025 budget.
