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Forth Road Bridge facts and figures

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  • The Forth Road Bridge is a long-span suspension bridge which was opened on September 4, 1964, by Her Majesty Queen Elizabeth II.
  • Construction began in 1958 and the project cost £19.5 million.
  • Over 24 million vehicles cross the bridge each year.
  • Nearly 40,000 tonnes of steel and 125,000 cubic metres of concrete went into its construction.
  • When it opened, it was the first bridge of its kind in the UK, the longest outside the USA and the fourth longest in the world. It features a dual two-lane carriageway and cycletracks/footpaths.
  • The full length of the bridge is 2.5 km, which includes a main span of 1,006m between the two main towers, side spans of 408m each and north and south viaducts of 252m and 438m respectively.
  • 49,280 km (30,000 miles or 6,350 tonnes) of wire make up the two main cables from which the suspended deck hangs. Each cable is 590mm in diameter and made of 11,618 high-tensile wires, each 4.98mm-thick.
  • These main cables each take 13,800 tonnes of the total load and are anchored into the rock on both sides of the Forth. The anchorages are made of concrete cast in tunnels between 56 and 79m in length of tapering section cut into the rock at an inclination of 30° to the horizontal. The concrete is strengthened by steel post-tensioning strands grouted into conduits.
  • road-rainbowThe bridge’s two main towers stand over 150m above the mean water level, support the majority of the bridge’s weight, and are of welded cellular high-tensile steel construction, featuring steel up to 25mm thick. The towers were strengthened in the late 1990s to support the ever-increasing weights of heavy goods vehicles crossing the bridge.
  • The north tower stands on the Mackintosh Rock while the south tower features caissons founded on sandstone some 32m below high water. Defences around both piers were added in the late 1990s to withstand potential collisions from shipping.
  • The side towers are located where the approach viaducts meet the suspended span. These substantial reinforced concrete structures help to support the weight of the main cable as well as both approach viaducts.
  • The suspended span decks hang from the bridge’s two main cables by 768 steel hanger ropes of 48mm (main span) and 57mm (side span) in diameter that are between 2.4 and 90 m long. These hanger ropes were all replaced between 1998 and 2000 and each set of four takes loads of 176 and 224 tonnes.
  • The bridge’s suspended deck is 36m wide but no more than 38mm thick. It consists of a steel stiffening truss with three longitudinal air gaps at roadway level to improve aerodynamic stability.
  • As the roadway expands and contracts according to varying temperature, wind and weight of traffic, expansion joints are embedded in the roadway under the two main towers.