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Theoretical mechanics

Crowd synchrony on the Millennium Bridge

Footbridges start to sway when packed with pedestrians falling into step with their vibrations.


Soon after the crowd streamed on to London's Millennium Bridge on the day it opened, the bridge started to sway from side to side: many pedestrians fell spontaneously into step with the bridge's vibrations, inadvertently amplifying them. Here we model this unexpected and now notorious phenomenon — which was not due to the bridge's innovative design as was first thought — by adapting ideas originally developed to describe the collective synchronization of biological oscillators such as neurons and fireflies. Our approach should help engineers to estimate the damping needed to stabilize other exceptionally crowded footbridges against synchronous lateral excitation by pedestrians.

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Figure 1: Effect of pedestrian crowding on London's Millennium Bridge.
Figure 2: Simulated outbreak of wobbling and crowd synchronization on the Millennium Bridge.


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Correspondence to Steven H. Strogatz.

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The authors declare no competing financial interests.

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Strogatz, S., Abrams, D., McRobie, A. et al. Crowd synchrony on the Millennium Bridge. Nature 438, 43–44 (2005).

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