Clever engineering means that the Forth Road Bridge ‘breathes’ and adapts to cope with the extremes of the Scottish climate.
Chris Tracey, Engineering Manager, explained: "The Forth Road Bridge was engineered to move with the weather conditions and load, not against them.
"Built-in expansion joints at the approach viaducts and the main towers underneath the decks allow the structure to expand and contract according to changes in temperature, wind speed and weight of traffic.
"Without these, the crossing’s main towers would need extreme reinforcement to keep the structure rigid.
"Joints on the bridge’s main deck can expand and contract for total movement of 1.73 metres, while the middle section of the span can swing over 7 metres side to side in very strong winds and 4 metres up and down due to temperature and weight changes.
"Drivers in moving cars are unlikely to notice these movements, but those standing still on the bridge are often aware that the ‘solid’ structure is actually moving in all directions!
“Of course, while the bridges are built to cope with everything the climate can throw at them, the same doesn’t apply to people and traffic using them.
“That’s why Bridge Control staff constantly monitor weather conditions in case drivers need to be told to slow down, high-sided vehicles need to kept off the bridge or – in extreme cases – the bridges have to be closed to traffic.”