The Forth Road Bridge when opened, on 4 September 1964 by Her Majesty Queen Elizabeth II, was the largest suspension bridge in Europe, and, together with the approach viaducts is over 2½ km. (over 1½ miles) long.
The bridge has a spectacular central span of over 1 km. (3300 ft.) between its two main towers. The side spans, which carry the deck to the side towers, are each 408 m. (1340 ft.) long and are flanked by approach viaducts.
At the side towers the supporting cables turn down towards the anchorages which are, essentially massive wedges built by tunneling into the rock. The cables are 610 mm. (2 ft.) in diameter and were spun on site using 11618 parallel high tensile steel wires 5 mm. (0.196 ins.) in diameter.
The main towers extend 156 m. (512 ft.) above mean river level and the sag of the cables between the towers is approximately 91 m. (300 ft.). The clearance for shipping below the deck of the main span is 46 m. (150 ft.) close to the towers and this increases to 50 m. (163 ft.) at mid-span.