The Lower Thames Crossing has reached another major milestone after National Highways announced the company that will build the giant tunnel boring machine set to excavate the UK’s longest road tunnel.

The enormous machine, which will be built by German engineering firm Herrenknecht, is expected to arrive on site in 2028 and will begin digging the twin tunnels beneath the River Thames as construction of the new crossing gathers pace.

Measuring 16.4 metres in diameter, the machine will be the largest tunnel boring machine ever used in Europe and the third largest in the world. At around 120 metres long and weighing more than 5,000 tonnes, it will be transported to the UK in sections by sea before travelling up the Thames to the Port of Tilbury.

Once assembled, the machine will excavate two parallel tunnels, each stretching for 2.6 miles beneath the Thames. The tunnels will carry three lanes of traffic in each direction, making them more than twice the size of the existing Dartford tunnels and becoming the longest road tunnels in the UK.

The Lower Thames Crossing is designed to increase road capacity east of London, providing an alternative to the heavily congested Dartford Crossing and improving connections between the South East, the Midlands and the North.

National Highways says the project has been designed with sustainability in mind, with around 80 per cent of the 14.3-mile route either in tunnel, within cuttings or behind landscaped embankments to reduce its visual impact. The organisation also aims to make it the first major UK infrastructure project to achieve carbon-neutral construction through measures including the use of low-carbon concrete and other environmentally focused construction techniques.

Shaun Pidcock, Delivery Director for the Lower Thames Crossing, said:

“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. 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.”

The machine will be operated by the Bouygues Travaux Publics Murphy Joint Venture, which is delivering the tunnels and their approaches. Engineers say it has been specially designed to cope with the challenging ground conditions beneath the Thames, tunnelling through clay and chalk at depths of up to 60 metres below the riverbed.

Construction of the Lower Thames Crossing began earlier this year following government approval and funding. The new road is expected to open in the early to mid-2030s.