The construction of the longest railway bridge in Britain, a massive undertaking estimated to cost £1.6 billion, is almost complete. After it is finished, the River Colne Viaduct will stretch over two miles, connecting the Chiltern and London tunnels of HS2. A thousand deck parts, each weighing 140 tonnes—700 times the average weight of the blue whale, the largest mammal in the world—are used in its construction. Express.co.uk was exclusively told that as of February 2024, 700 of the deck segments have been installed. The bridge is more than halfway complete works continues from north to south. The bridge has been under construction since 2021, with bridge-building machines and their teams working to build over the Colne Valley Park near Denham. Building.co.uk estimates that the project, which is one of the biggest single civil engineering projects of HS" Phase One, will cost about £1.6 billion. When trains begin operating in six to ten years, the Colne Valley will provide HS2 travellers with their first glimpses of country life after departing from London. With a series of arches carrying the railway 10 metres over the lakes, river, and canal, the design was influenced by the way a stone skipping across the water. When it opens, trains will be able to cross the entire viaduct in 40 seconds at a speed of up to 200 mph. The design was inspired by the flight of a stone skipping across the water, with a series of elegant spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal. The Minister for HS2 and Rail Huw Merriman walked on the first stretch of the viaduct last January to appreciate the "extraordinary feat of engineering and architecture." A spokesman for HS2 told Express.co.uk: "Works to build the viaduct are part of our civil engineering main works. After that stage of construction will come the rail systems fit out, which includes track laying, and installation of both overhead electrical wires and noise barriers." Phase One of HS2 will connect London and Birmingham, with trains able to make the trip in just 49 minutes. It is scheduled to open between 2029 and 2033. Phase Two, which would have connected Birmingham to Manchester, was cancelled in October 2023. Rishi Sunak announced it would abandoned, despite a track having been built to Handsacre.