UK’s High Speed Two (HS2) has begun excavation of the last tunnel bore on its 140-mile high-speed rail link between central London and the West Midlands.
On 16 March 2026, the 11th and final tunnel boring machine (TBM), named Karen, commenced its journey from Old Oak Common station in west London towards the planned terminus at Euston.
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The TBM is named after Karen Harrison, among the UK’s first female train drivers, who previously drove trains out of Old Oak Common depot.
The new phase follows the launch of TBM Madeleine, which began work on the first bore of the twin-bore Euston Tunnel in January.
Together, these machines will construct the 4.5-mile twin-bore Euston Tunnel, enabling Britain’s high-speed trains to run directly in and out of central London.
HS2 states this infrastructure aims to increase rail capacity and improve journey times.
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By GlobalDataTo mark the milestone, Avanti West Coast invited two female train drivers, Hayley Richardson and Vicky Knight, to operate TBM Karen alongside engineers during its launch.
The naming of the TBM continues the tradition of naming tunnelling equipment after notable women.
HS2 Line of Route delivery director Alan Morris said: “The launch of the final HS2 TBM towards Euston is significant milestone in our extensive tunnelling programme. TBM Karen will complete the second bore of the Euston Tunnel, bringing high-speed train services directly in and out of the centre of the capital, enabling future economic growth and regeneration.
“While we have been working hard to reset the project, our expert teams have been focused on safely driving up productivity – and today’s final TBM launch is real evidence of that paying off.”
Construction at Euston remains part of a wider government commitment to regenerate the area through a new HS2 station, which is expected to encourage further investment and create employment opportunities.
HS2 is currently undergoing a “comprehensive reset” under chief executive Mark Wild to re-sequence construction activities and clarify costs and timelines.
The Skanska Costain STRABAG joint venture is leading the construction of this second bored tunnel beneath London, following completion of the Northolt Tunnel.
Four other tunnels along the route, namely Northolt, Chiltern, Long Itchington Wood and Bromford, have already been excavated.
Manufactured by Herrenknecht in Germany before assembly at Old Oak Common, TBM Karen measures 198m in length and operates continuously underground.
The machine excavates earth while installing concrete segments manufactured by STRABAG in Hartlepool; these are then transported by rail to London.
Across both bores of the Euston Tunnel, workers will install over 48,000 concrete segments and remove 1.5 million tonnes of spoil.
A dedicated logistics tunnel, the Atlas Road Logistics Tunnel, completed in January 2024, supports this operation by providing access for materials delivery and spoil removal.
Excavated material travels via conveyor to Willesden Euro Terminal Depot before being transported by rail for reuse elsewhere in Kent, Cambridgeshire and Warwickshire; this process reduces road haulage by more than 135,000 lorry movements.
The current tunnelling works begin 23m below ground at Old Oak Common; at its deepest point, the Euston Tunnel will reach 66m below surface level.
Upon completion, teams will park TBM Karen underground and retrieve key components for reuse. The machine’s cutterhead will be extracted from Euston Cavern while its shield will remain in place behind a reinforced concrete lining.
During its drive towards central London, TBM Karen passes beneath Kensal Green cemetery, where Isambard Kingdom Brunel is buried.
Avanti West Coast continues to operate intercity services on the West Coast Main Line linking London with cities including Birmingham, Manchester, Liverpool, Glasgow and regions in North Wales.
