Europe's Largest Tunnel Boring Machine Chosen for Lower Thames Crossing

Record-breaking 16.4-metre TBM to construct Britain's longest road tunnel beneath the River Thames

Construction of the Lower Thames Crossing has reached another major milestone after National Highways confirmed the appointment of the company that will build the record-breaking tunnel boring machine (TBM) destined to excavate Britain's longest road tunnel.

The enormous machine, which will become the largest tunnel boring machine ever deployed in Europe, is expected to arrive on site in 2028, marking the next major stage in the delivery of one of the UK's most significant transport infrastructure projects.

Once operational, it will excavate twin tunnels beneath the River Thames, helping create a new strategic crossing east of Dartford and significantly increasing road capacity between Kent and Essex.

A machine built on an unprecedented scale

Designed with a diameter of 16.4 metres, the TBM will rank as the third largest ever constructed worldwide.

Stretching approximately 120 metres in length and weighing more than 5,000 tonnes, the giant machine will be manufactured in Germany before being dismantled into transportable sections for shipment to the UK.

The components will travel by sea before being transported along the River Thames to the Port of Tilbury, where assembly will take place ahead of tunnelling operations.

A single TBM will excavate both tunnel bores, with the machine returning to its launch point after completing the first drive to begin work on the second—an approach intended to reduce both construction costs and carbon emissions.

Britain's longest road tunnel

The Lower Thames Crossing will include a 2.6-mile twin-bore tunnel, making it the longest road tunnel in the UK.

Each tunnel will accommodate three lanes of traffic, offering considerably greater capacity than the existing Dartford tunnels and helping relieve one of the country's most congested sections of the strategic road network.

National Highways says the new crossing will effectively double road capacity across the Thames east of London while improving connections between ports in the South East, the Midlands and northern England.

Engineering designed around the environment

Rather than constructing a bridge across the river, planners opted for a tunnel to minimise impacts on nearby communities and protect internationally important wetland habitats along the Thames Estuary.

Around 80% of the scheme's 14.3-mile route will either be contained within the tunnel itself, built below ground in cuttings or screened behind landscaped embankments to reduce its visual impact.

The tunnel boring machine itself has also been designed to operate through a wide range of geological conditions, including clay, chalk and groundwater up to 60 metres beneath the riverbed, using advanced variable density technology.

Powered entirely by electricity sourced from renewable energy, the machine incorporates several new engineering innovations intended to improve safety, efficiency and operational flexibility throughout construction.

Carbon reduction at the heart of the project

National Highways continues to position the Lower Thames Crossing as its most environmentally ambitious road scheme to date.

Project teams say significant reductions in embodied carbon have already been achieved through changes to the design and construction methodology.

Among the measures planned are the use of low-carbon concrete for the tunnel lining, optimised engineering designs that reduce the volume of materials required and construction techniques intended to minimise emissions throughout delivery.

The organisation believes these measures will enable the Lower Thames Crossing to become the UK's first major infrastructure project to achieve carbon neutrality during construction.

International expertise behind the project

The TBM will be manufactured by Herrenknecht, whose previous projects include machines used on the Elizabeth line, Silvertown Tunnel, HS2 and the Thames Tideway Tunnel.

Construction of the tunnels will be undertaken by the Bouygues Travaux Publics Murphy Joint Venture, which will oversee operation of the machine throughout excavation.

Shaun Pidcock, Delivery Director for the Lower Thames Crossing, said appointing the supplier represented another important step towards delivering what National Highways describes as Britain's greenest road while reducing carbon emissions and protecting the surrounding environment.

Bouygues and Herrenknecht also highlighted the machine's bespoke design, describing it as incorporating a number of industry-first innovations that will improve tunnelling performance while maintaining high safety standards.

Momentum building towards 2028

Although enabling works are already underway, the arrival of the giant TBM in 2028 will represent one of the most visible milestones in the project's construction programme.

If delivered to the current timetable, the Lower Thames Crossing is expected to open in the early to mid-2030s, providing a new strategic route beneath the Thames and transforming connectivity across one of the UK's busiest freight and transport corridors.