HS2’s Colne Valley viaduct is now officially the UK’s longest railway bridge after the completion of civil engineering works, taking the title from the Tay Bridge linking Fife and Dundee, which had held the record since 1887.

At 2.1 miles long, the structure is the longest of more than 50 major viaducts being built for HS2, and carries HS2 across roads, lakes, the River Colne, and the Grand Union Canal.

It is formed of 1,000 uniquely-shaped deck segments, and stretches across the Colne Valley near the M25 motorway and the village of Denham in Buckinghamshire.

It is located between the 8.4-mile-long Northolt Tunnel beneath London and the 10-mile-long Chiltern Tunnel.

HS2’s main works contractor for this section of the route, Align, a joint venture between Bouygues Travaux Publics, VolkerFitzpatrick and Sir Robert McAlpine, started construction of the 10-metre-tall viaduct in March 2021. After the last giant pre-cast deck segment was lowered into place in September 2024, work continued with Align putting the finishing touches to the structure, including installing parapet sections, noise barriers, a structural health monitoring system, waterproofing and drainage.

“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.”

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

“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.”

Coralie Peroux, Align JV project director