Forth Road Bridge - South Queensferry, Edinburgh. - Suspension Bridges on Waymarking.com

Increasing road traffic had first set about the idea of a road crossing over the Firth of Forth in the 1920s, but the Great Depression and World War Two set things back until 1947 when a suitable point was found just upriver from the railway bridge between North and South Queensferry.

Work began in September 1958 with Freeman Fox & Partners and Messrs Mott, Hay & Anderson overseeing the design and construction. The construction was carried out by Sir William Arrol & Company, Cleveland Bridge & Engineering Company and Dorman Long ( Bridge & Engineering) Ltd. These all joined forces to form the ACD Bridge Company.

By 1961 the cable anchorages and two main towers were in place and two years later the box girders were in place which completed the main span. In 1964 the asphalt for the roadway and footpaths was in place along with the lighting. At the completion £19.5 billion was spent on the bridge which was opened by Queen Elizabeth II on September 4th 1964.

At the time of completion the bridge was the fourth longest in the world and the longest outside of the United States. The main span between the two towers is 1006 metres with an overall length of 2.5km or 1.5 miles. The southern approach viaduct is 438 metres long and the northern viaduct 253 metres. The towers are 156 metres high and constructed of a welded cellular high tensile steel.

39,000 tonnes of steel was used and 125,000 cubic metres of concrete. In the cables are 11,618 individual high tensile steel wires compacted into a bundle 60cm thick. In total length they would circumnavigate the world one and a quarter times. The cables are anchored at each end to take the strain of 13,800 tonnes of total load in each cable. There are 768 steel hanger ropes, 57mm diameter in the side spans, 48mm diameter in the main span. At the lowest point they are 2.4 metres high and at the highest, 90 metres high.

Fraying hanger ropes on the west side meant that all had to be replaced and strengthened between 1998 and 2000, and the bridge saw continual work to cope with increasing traffic in the early 21st century.

It was then decided that another bridge would be built upriver to the west to lighten the load on the ageing bridge. Named the Queensferry Crossing, it is a cable-stayed bridge with three tall towers that will carry the M90 motorway. It was opened by Queen Elizabeth again, in early September 2017.

Now sandwiched between the old railway and new road bridges, the Forth Road Bridge will now carry public transport over the Forth, along with cyclists and pedestrians.