The current pair of twin suspension bridges spanning the Tacoma Narrows strait of Puget Sound in Washington succeed the original engineering debacle, which infamously collapsed into the water below during windy conditions on November 7, 1940. Any such historical reference to the original structure is usually iterated for educational purposes, with breathtaking images of the collapse embedded within thousands of science and engineering textbooks. The catastrophic engineering failure would strengthen research into bridge aerodynamics and aerolastics, research that continues to influence the design of long-span bridges around the world.

The doomed Tacoma Narrows Bridge on opening day, July 1, 1940, image via University of Washington Libraries Digital Collections

Plans to install the integral vehicular link date back as far as 1889, when the Northern Pacific Railway first drafted concepts for a trestle bridge. But it wasn't until the 1920s that a bridge had become a matter of serious consideration. It took time for the idea to gather steam, and it finally did in 1937, when the Washington State Toll Bridge Authority was created, and $5,000 was given towards studying a bridge over the Narrows.

The bridge violently sways moments before its collapse, image via Wikimedia Commons

Construction would begin a year later following a finalized design by Leon Moisseiff. Workers had inauspiciously taken to calling the bridge "Galloping Gertie" because of the visible vertical movement of its deck on particularly windy days, an omen for what was to come. The two-lane bridge was the third-longest suspension bridge in the world when it opened on July 1, 1940, behind only the Golden Gate Bridge and the George Washington Bridge in New York City

The bridge's solid and impermeable sides did not allow wind to pass through, and the road violently swayed and collapsed just four months after entering service. A Cocker Spaniel, too frightened to escape an abandoned and oscillating car, was the only casualty. Dismantling of the remaining structure would continue until 1943, but the onset of the Second World War and ongoing financial issues would indefinitely delay work to replace the bridge.

The 1950 (right) and 2007(left) Tacoma Narrows Bridge, image via Washington State Dept of Transportation

The successor to the ill-fated bridge, today serving westbound traffic, would open on October 14, 1950 at an even longer 1,822 metres. Finding humour in the much-publicized ordeal, and rejoicing over what was a much stronger span, the locals nicknamed the replacement "Sturdy Gertie." A proposal to build a second Narrows span was approved by voters in 1998, with construction beginning four years later, and completion marked in 2007. Together, the twins are the fifth-longest suspension bridge spans in the United States.

Tacoma Narrows Bridge, image by Flickr user Pat Kight via Creative Commons

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