HS2 Colne Valley viaduct completed as UK’s longest high-speed rail bridge opens

Credit: Hs2

New images have been released to mark the completion of civil engineering works on HS2’s Colne Valley viaduct, the UK’s longest rail bridge.

The 2.1-mile-long structure carries Britain’s high-speed railway across roads, lakes, the River Colne and the Grand Union Canal, north west of London. Trains will operate at 200mph on the viaduct’s gentle curve, which is formed of 1,000 uniquely shaped deck segments.

Construction of the 10 metre-tall viaduct began in March 2021, led by HS2’s main works contractor for this section, Align, a joint venture between Bouygues Travaux Publics, VolkerFitzpatrick and Sir Robert McAlpine. The final pre-cast deck segment was lowered into place in September 2024.

Since then, Align has installed parapet sections, noise barriers, a structural health monitoring system, waterproofing and drainage. The completion means that the Tay Bridge, linking Fife and Dundee, has ceded its crown as Britain’s longest rail bridge, a record it had held since 1887.

Mark Wild, HS2 Ltd’s chief executive, is leading a comprehensive reset of the programme to deliver the railway efficiently and at the lowest reasonable cost, while work continues along the 140-mile route between London and the West Midlands.

Billy Ahluwalia, HS2 Ltd’s senior project manager for the viaduct, said:

“The completion of the viaduct marks more than 10 years of planning, design and construction. I’m immensely proud of the level of dedication and professionalism shown by the whole team to maintain high standards of safety and quality, working over land and water to deliver. It’s a remarkable achievement. The viaduct is a structure of international significance, a stunning feat of engineering that will no doubt stand the test of time.”

Coralie Peroux, Align JV project director, said:

“I’m immensely proud of the Align team and our supply chain partners, not just for successfully completing the UK’s longest rail bridge, but for the remarkable way they delivered it. Faced with the technical challenges in design and construction, they harnessed their expertise, worked as an integrated project team, and embraced collaboration. Their efforts have produced a striking HS2 landmark and created a valuable learning legacy for future designers, engineers and construction professionals.”

The viaduct stretches across the Colne Valley near the M25 motorway and Denham village. It sits between the 8.4-mile Northolt Tunnel and the 10-mile Chiltern Tunnel. It is the longest of more than 50 major viaducts being built for HS2, which will operate on dedicated tracks between London and Birmingham and beyond, boosting capacity on the busiest section of the West Coast Main Line while driving economic growth.