This footbridge, is a steel suspension bridge for pedestrians to cross the River Thames in London. It links Bankside from St Paul’s Cathedral with the City of London at the Modern Tate museum. Londoners nicknamed the bridge the “Wobbly Bridge” after participants in a charity walk on behalf of Save the Children to open the bridge felt an unexpected and, for some, uncomfortable swaying motion on the first two days after the bridge opened. The bridge was closed later that day, and after two days of limited access the bridge was closed for almost two years while modifications were made to eliminate the wobble entirely. It only reopened in 2002. I must admit, I didn’t feel any wobble even after jumping up and down a couple of times!
The wobble was attributed to an under-researched phenomenon whereby pedestrians crossing a bridge that has a lateral sway have an unconscious tendency to match their footsteps to the sway, thereby exacerbating the sway. The tendency of a suspension bridge to sway when troops march over it in step was well known, which is why troops are required to break step when crossing such a bridge.