The Colne Valley Viaduct is officially the UK’s longest railway bridge, stretching just over two miles long between HS2’s London and Chiltern tunnels
The UK’s longest railway bridge, the Colne Valley Viaduct, has been officially completed.
Stretching just over two miles between HS2’s London and Chiltern tunnels, the impressive structure was constructed using a thousand concrete deck segments, each weighing a hefty 140 tonnes – more than the average weight of the world’s largest animal, the blue whale.
Work on the bridge began in 2021, with construction teams and their machines tirelessly building over the Colne Valley Park near Denham. Once trains start running, passengers leaving London will be treated to their first views of the countryside from the bridge.
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Trains will be able to travel at speeds of up to 200mph, crossing the entire viaduct in a mere 38 seconds. The design of the bridge, one of the largest single civil engineering works of HS2 Phase One, was inspired by the image of a stone skipping across water, with a series of spans carrying the railway 10m above the lakes, river and canal.
Naz Huseinmiya, one of the construction managers, expressed her pride in working on the project to The Telegraph, saying: “I worked on Crossrail a decade ago and now I use the Elizabeth Line myself.” She added: “I love seeing the infrastructure you’ve helped create used by millions of people.”
Fellow engineer Katy Hodgson echoed this sentiment, stating: “I love it. Every time I go by, I nod to it and say, ‘I built that'”. The Colne Valley Viaduct, completed in August 2025 at a cost of £1.6 billion, has taken the title of the UK’s longest railway bridge from Scotland’s Tay Bridge. The viaduct, along with the nearly 10-mile Chiltern Tunnel, is part of the HS2 project, reports the Express.
Post-construction, the factory and surrounding buildings will be removed, transforming the entire area between the viaduct and the Chiltern Hills tunnel into chalk grassland and woodland. This transformation is part of HS2’s ‘Green Corridor’ initiative.
In 2024, the Colne Valley Viaduct was recognised for its architectural beauty, winning the Engineering Award at the Royal Fine Art Commission Trust’s Building Beauty Awards. Despite its grand scale, judges commended the structure, located northwest of London, for its ability to “tread lightly” and blend seamlessly with its surroundings.
HS2’s Phase One, which will link London and Birmingham, promises a travel time of just 49 minutes. It is expected to be operational between 2029 and 2033.
However, Phase Two of the project, which would have connected Birmingham to Manchester and Leeds, was scrapped in October 2023. Chancellor Rishi Sunak announced the cancellation, despite a track having already been built to Handsacre.