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The River Forth was first bridged by the Forth Bridge in 1890, a monumental piece of railway engineering and an iconic landmark. In 1964 the Forth Road Bridge opened to traffic and since then the narrowing of the Forth between Queensferry and North Queensferry has been home to two world class bridges. And if all goes to plan, some time in 2017 a second Forth Road Bridge will open to traffic, taking a line to the west of the existing bridges. The header image is Transport Scotland's impression of what, by then, could well be the most impressive concentration of very large bridges anywhere in the world.
Why a second Forth Road Bridge? The existing road bridge has for many years been carrying volumes of traffic far in excess of what was expected at the time it was built. This has led to structural loads much larger than originally forecast, and has also caused one of Scotland's worst bottlenecks, especially for traffic heading south from Fife to Edinburgh on weekday mornings. Additionally, in recent years corrosion has begun to appear in the steel strands making up the main suspension cables. The two factors have together resulted in fears that use of the bridge by heavy vehicles might have to be restricted within a decade, and that it might have to close altogether by 2020.
Work is under way to see if the suspension cables on the existing bridge can be replaced or strengthened, but even if this is technically possible, the work will cause considerable disruption for a prolonged period of time. The Scottish Government has therefore also looked at building a new crossing over the river, something first considered but not pursued in the 1990s. After a review of various bridge and tunnel options, the Government announced in late 2007 that it intended to build a cable-stayed bridge designed to carry both road traffic and trams.
The aim is to begin construction on the new bridge in 2011, with completion taking 5½ years. So even on the most optimistic of projections, it is not clear that a new bridge can be completed before it becomes necessary to place restrictions on the existing bridge. What this all amounts to over the next few years is a large "watch this space". Will the existing bridge be fixed or strengthened in time to avoid traffic restrictions or closure? Will the new bridge be built in time to prevent major disruption? A lot of people, especially people who live in Fife and work in Edinburgh, are anxiously waiting to find out.
The scale of the traffic problem is clear from a few headline figures. Before the Forth Road Bridge was built, anyone wanting to cross to Fife from Edinburgh took a vehicle ferry from Queensferry to North Queensferry. By the late 1950s, the four ferries on the route were between them making 40,000 crossings each year and carrying 1.5 million people, 600,000 cars and 200,000 goods vehicles. In its first full year of operation, 1965, the Forth Road Bridge carried around two million vehicles in each direction. By 2003 some 12,000,000 vehicles were crossing the bridge each year in each direction, of which over 700,000 were heavy good vehicles. And in the meantime the maximum permissible weight of a lorry on UK roads has increased from 24 tonnes to 44 tonnes.
Meanwhile the Scottish Government elected into power in 2007 arrived with a commitment to remove tolls on Scotland's two remaining toll bridges, the Forth Road Bridge and the Tay Bridge. Removing tolls from a bridge whose future is endangered partly by the growth in traffic levels might seem a rather odd thing to do: but the levels of the tolls were so low (£1 for a car, charged northbound only) that their removal probably isn't going to make that much difference to the overall life expectancy of the bridge. Either way, tolls were removed on 11 February 2008.
Construction of the first Forth Road Bridge began in 1958. When it was opened in 1964 it was the longest suspension bridge in Europe and the fourth longest in the world. The central span is 3300ft long, and is flanked by side spans each 1340ft long. The total length between abutments, counting the viaducts at each end, is 8259ft. The bridge cost some £19.5m to build, though this figure included the cost of 13km of dual carriageway, 13km of other roads and 24 minor bridges. It used some 39,000 tons of steel (about two thirds the amount used in the Forth (Rail) Bridge), not counting the 30,800 miles of wire, weighing 7,900 tons, in the suspension cables. The clearance for shipping below the centre of the bridge is 163ft, and 150ft near the towers.
The cable-stayed bridge announced at the end of 2007 will have two main spans of 650m each and two further spans of 325m each (making it around 400ft longer than the existing road bridge), supported by three towers.