London Opens the Millennium Bridge. Pedestrians Make It Wobble.

Then the bridge began moving.

The Millennium Bridge was supposed to look effortlessly modern.

A thin steel crossing stretched across the Thames between St Paul’s Cathedral and Tate Modern, linking two parts of London with what its designers called a “blade of light.”

It opened to the public on Saturday, 10 June 2000.

Approximately 90,000 people crossed it that day.

Then the bridge began moving.

Not collapsing.

Not breaking apart.

Wobbling.

Large crowds exposed an unanticipated lateral instability. As the deck moved beneath them, pedestrians naturally adjusted their balance. Those responses interacted with the bridge and amplified its sideways motion.

The exact engineering mechanism is subtler than the familiar explanation that everybody simply began walking in step. Later research has questioned whether synchronized footfalls initiated the instability at all.

The visible result was considerably less subtle.

London had just opened its first new Thames crossing in a century and immediately acquired a new nickname for it:

the Wobbly Bridge.

Access was restricted after opening day. Within three days, the bridge was closed for investigation.

That might sound like the end of the embarrassment.

Instead, it became an engineering research problem.

The bridge was not about to collapse, but its movement made normal pedestrian use unacceptable. Engineers studied the interaction between people and the unusually flexible structure, then installed extensive damping systems to control the motion.

The repairs took considerably longer than the bridge’s first period of public operation.

It reopened in February 2002 and became one of London’s familiar landmarks.

But its opening weekend had already produced an unusually efficient piece of civic branding.

Millions had been spent creating the Millennium Bridge.

Londoners needed roughly one day to rename it according to the first thing it did.