High-speed rail network HS2 has taken another major step forward in its construction through the London Borough of Ealing, as one of its giant tunnelling machines completed a five-mile underground journey.
The tunnel boring machine (TBM), named Caroline, reached the Green Park Way vent shaft in Greenford today (3 April 2025), having installed 4,217 concrete rings since launching in October 2022. The milestone marks continued progress for the rail project’s London tunnels, part of a wider effort to connect the capital with the Midlands and the North.
The 2,050-tonne machine is the second to complete the western section of the Northolt Tunnel, part of the high-speed rail line between West Ruislip and Old Oak Common.
Caroline is one of four TBMs building the 8.4-mile twin-bore tunnel. Two machines have worked from the west, with two more currently digging from the east towards Green Park Way.
Malcolm Codling, client director for HS2 Ltd, said: “We’re immensely proud of the work we have done to complete the second breakthrough for the Northolt Tunnel underneath the capital. As we focus on delivering Britain’s new high speed railway between London and the West Midlands, we are gearing up for our most productive year to date on this stretch of the line.”
Caroline was named by pupils at Brentside Primary Academy in Ealing after the 18th-century astronomer Caroline Herschel. The first TBM on this route, Sushila, completed its drive in January and has already been lifted out.
The two eastern machines were launched from HS2’s Victoria Road Crossover Box, just outside Acton’s Old Oak Common station. HS2 Ltd said 93% of the Northolt Tunnel is now complete, with the final sections due to be finished later this year.
