HS2’s Colne Valley viaduct becomes Britain’s longest as final segment is lowered into place

A new milestone has been reached in the construction of the HS2 railway with the structural completion of the Colne Valley viaduct in west London -which is now the longest viaduct in the UK.The viaduct rises out of the tunnel under the M25 and carries the HS2 railway over the Colne Valley—a nature reserve created from flooded gravel pits—before dipping back down into the tunnels at Ruislip. The low-level design, often below the level of the surrounding trees, has several long shallow