The 2.1 mile-long structure carries the railway across a series of roads, lakes, the River Colne and the Grand Union Canal, north west of Hillingdon. Work on the 10 metre-tall viaduct started in March 2021 and the last of the giant segments was lowered into place in September 2024. It means the Tay Bridge, linking Fife and Dundee, has finally ceded the crown of Britain’s longest rail bridge, a record it had held since 1887. Mark Wild, HS2 Ltd’s chief executive, has announced he is leading a reset to finish the project in the most efficient way, for the lowest reasonable cost. Billy Ahluwalia, HS2 Ltd's senior project manager for the viaduct, said: “It’s a remarkable achievement.