the bridge showed that, while the bridge itself would be stable, the presence of the adjacent railway bridge would cause severe oscillation. The finally accepted design was for a steel through arch bridge with a single carriageway. The design of the bridge is similar to that of Sydney Harbour Bridge but differs from it in that the side spans are continuous with the main span rather than being separate from them. This design feature was necessary to avoid the problem of oscillation due to the railway bridge. The main span measures and each side span is . Construction Construction began on 25 April 1956. The contractors for the first phase of work, Leonard Fairclough of Adlington, cleared the ground and constructed the foundations for the piers. The contract for the second phase, the building of the main arch and the side arches, was given to Dorman Long of Middlesbrough who sub-contracted the building of the bridge deck, viaduct and roadworks to Leonard Fairclough. Building of the bridge itself began in March 1958 and the side spans were completed by November 1959. The main arch was built by cantilevering steelwork from the side spans until it met in the middle in November 1960. The carriageway was suspended from the arch by 48 lock-coil wire ropes. From February 1960, approach roads and viaducts were being built on both sides of the river; the total length of viaduct constructed was . The approaches on the Runcorn side blocked the Bridgewater Canal at Waterloo Bridge and the line of locks leading down to the Mersey were filled in. The bridge was officially opened as the Runcorn-Widnes Bridge by Princess Alexandra on 21 July 1961. Since creation it has always been painted in a light shade of green. Structure, specifications and costs The main arch is long and each side arch measures . During its construction 720,000 rivets were used. Its height over the river bed is and the headroom over the ship canal is . During its construction 5,900 tons of steel were used and 7,500 tons of concrete. The bridge requires constant repainting, with each coat using of paint. On the Runcorn side the approach viaducts are in length, and on the Widnes side . The cost of constructing the bridge was £2,433,000. At the time of its construction it had the third longest steel arch span in the world. It had the