The Colne Valley Viaduct, part of the HS2 project, has now become the longest railway bridge in Britain, surpassing the Tay Bridge’s 137-year reign.
Stretching 3.4 kilometers (2.1 miles) across the Colne Valley near the M25 motorway and Denham, the viaduct will carry high-speed trains to and from London at speeds of up to 320km/h (200mph).
Constructed by Align JV (Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick), the viaduct is one of over 500 bridging structures on the HS2 route, including wildlife-friendly “green bridges” and footbridges. The build process started in May 2022, with the final segment placed in September 2024.
A 160-meter-long launching girder was used to install 1,000 unique pre-cast concrete segments, each match-cast to ensure precision. These segments form a gracefully curved bridge supported by 56 piers, raising the line 10 meters above the valley.
As the civil engineering phase wraps up, the next step will be the installation of rail systems, transforming the viaduct into a fully operational part of the HS2 line, expected to be ready between 2029 and 2033. Once operational, HS2 will greatly reduce travel times between London and Birmingham and ease congestion on existing lines.
HS2 Senior Project Manager Billy Ahluwalia praised the efforts of the team, describing the completion of the viaduct as a “historic achievement” after more than a decade of planning and construction. Align JV’s Project Director Loïc Menard emphasized the collaborative efforts that brought the project to completion ahead of schedule.
In addition to its transportation function, the area surrounding the viaduct will be transformed into a chalk grassland and woodland as part of HS2’s “green corridor” initiative, highlighting the project’s commitment to sustainability.
