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. In 2017 a second Forth Road Bridge, the Queensferry Crossing, 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 planned 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 together resulted in fears that use of the bridge by heavy vehicles might have to be restricted within a decade.
Work continues 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 therefore 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 late in 2007 that it intended to build a cable-stayed bridge designed to carry road traffic.
Construction on the new bridge began in 2011, with completion planned to take 5 years. Meanwhile, it seems the deterioration of the existing bridge many not be happening as fast as previously feared, so concerns that restrictions might need to be placed on the 1964 bridge before the Queensferry Crossing is complete are unlikely to be realised, much to the relief of everyone who commutes across the bridge, and of every property owner in Fife.
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 had 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 didn't 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 3,300ft long, and is flanked by side spans each 1,340ft long. The total length between abutments, counting the viaducts at each end, is 8,259ft. 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 Queensferry Crossing now under construction 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.