Europe’s Largest Underground Caterpillar Set to Dig Britain’s Longest Road Tunnel

There are big construction machines, and then there are machines so large they sound like something from a science-fiction film.

The latest example comes from the Lower Thames Crossing project, where National Highways has selected German engineering giant Herrenknecht to build what will become Europe's largest tunnel boring machine (TBM).

The enormous machine will play a central role in creating the UK's longest road tunnel beneath the River Thames.

Measuring a staggering 16.4 metres in diameter, the TBM will be the largest ever used in Europe and the third-largest tunnel boring machine in the world.

Once assembled, it will stretch around 120 metres in length, weigh more than 5,000 tonnes and be capable of excavating two huge road tunnels beneath the Thames between Kent and Essex.

The machine has been commissioned as part of the £11 billion Lower Thames Crossing scheme, one of the UK's most ambitious infrastructure projects.

When completed, the crossing will feature a 4.2-kilometre twin-bore tunnel and become the longest road tunnel in Britain, significantly expanding road capacity east of London and providing an alternative to the heavily congested Dartford Crossing.

Getting the machine to the construction site will be almost as impressive as operating it.

Because of its enormous size, the TBM will be manufactured in Germany before being transported to Britain in sections by sea.

The components will travel up the Thames to the Port of Tilbury, where the machine will be assembled before beginning its underground journey in 2028.

The giant "underground caterpillar" will dig through challenging ground conditions up to 60 metres beneath the river, cutting through chalk and clay while creating two parallel tunnels capable of carrying three lanes of traffic in each direction.

What makes the project particularly interesting is its environmental focus. Despite its scale, the Lower Thames Crossing is being promoted as one of the UK's greenest major infrastructure schemes.

The tunnel boring machine will run on electricity from renewable sources, while low-carbon concrete will be used for tunnel linings.

The wider project aims to become the UK's first major infrastructure development to achieve carbon neutrality during construction.

For the construction industry, the contract represents another major achievement for Herrenknecht, whose machines have already helped build landmark British projects including the Elizabeth Line, HS2, the Thames Tideway Tunnel and the Silvertown Tunnel.

While drivers will not be able to use the new route until the early to mid-2030s, the arrival of Europe's largest tunnel boring machine marks a significant step forward.

For now, Britain's next great road project is preparing to unleash a mechanical giant beneath the Thames — one that will spend years quietly carving its way through the earth while helping reshape the country's transport network.