The Tacoma Narrows Bridge collapsed on November 7, 1940, just four months after opening, when 42 mph winds triggered violent oscillations that tore the structure apart. It remains one of the most dramatic engineering failures in history, captured on film and studied in physics classrooms ever since. The only fatality was a dog named Tubby, stranded in a car on the buckling deck. Today, two modern bridges carry traffic across the same stretch of water in Washington State.
Why the Original Bridge Was Vulnerable
The 1940 bridge was designed by Leon Moisseiff, a respected engineer who had worked on the Manhattan Bridge and consulted on the Golden Gate. His design for the Tacoma Narrows crossing was strikingly slender. The center span stretched 2,800 feet, but its deck was supported by solid steel plate girders only 8 feet deep and 39 feet wide. That made it one of the shallowest and narrowest stiffening structures of any long-span suspension bridge ever built.
The original project engineer, Clark Eldridge, had proposed a 25-foot deep open truss to stiffen the deck. Moisseiff replaced it with those 8-foot solid plate girders to cut costs and achieve a more elegant profile. Eldridge objected, but Moisseiff’s reputation carried the day. The shallow, solid-sided design turned out to be the bridge’s fatal flaw: instead of letting wind pass through an open truss, the flat plate girders acted like a sail.
Galloping Gertie’s Final Morning
From the day it opened in July 1940, the bridge had a visible bouncing motion in even moderate wind. Drivers crossing the span could watch cars ahead of them disappear and reappear as the deck rolled in gentle waves. Locals nicknamed it “Galloping Gertie” and some thrill-seekers actually drove across it for fun. Engineers tried to stabilize the movement with tie-down cables and hydraulic dampers, but nothing worked.
On the morning of November 7, sustained winds of about 42 mph hit the bridge. At first the deck oscillated in its familiar up-and-down pattern. Then something changed. The motion shifted from vertical bouncing to a violent twisting, with one side of the roadway rising while the other dropped. The bridge was rotating at roughly 38 oscillations per minute, the deck tilting at extreme angles. Kenneth Arkin, a toll booth operator, closed the bridge to traffic.
A few people were still on the span. Leonard Coatsworth, a newspaper editor, abandoned his car and crawled on hands and knees to safety, leaving his daughter’s cocker spaniel Tubby in the back seat. Physicist Burt Farquharson, who had been studying the bridge’s movements for weeks, went back to try to rescue the terrified dog. Tubby bit his finger and refused to leave. Farquharson retreated moments before the stiffening girders buckled and a 600-foot section of roadway dropped into Puget Sound. The rest of the center span followed within minutes.
What Actually Caused the Collapse
For years, many textbooks described the failure as a resonance problem, comparing it to a singer shattering a wine glass. That explanation is incomplete. The actual cause was a phenomenon called aeroelastic flutter, a type of structural instability that occurs when wind interacts with a flexible solid surface. Flutter involves a feedback loop: wind pushes the structure, the structure’s movement changes how the wind flows around it, and that altered airflow pushes the structure even harder. The oscillations don’t just sustain themselves; they grow rapidly in amplitude.
In resonance, an outside force happens to match a structure’s natural frequency. In flutter, the structure generates its own destructive energy from the airflow. The shallow, solid plate girders of the 1940 bridge created the perfect conditions. Wind hitting the flat sides produced alternating vortices of pressure that fed into the deck’s twisting motion. Once the twisting began, there was no mechanism to absorb or counteract the energy. The amplitudes kept increasing until the steel gave way.
The 1950 Replacement Bridge
Construction on a replacement bridge began in 1949, and it opened to traffic in October 1950. Engineers applied the hard lessons of the collapse directly to the new design. The most critical change was replacing those solid 8-foot plate girders with a much deeper and wider open stiffening truss. The open truss allowed wind to pass through the deck structure rather than pushing against a flat surface, eliminating the conditions that produced flutter.
The new bridge also incorporated wind fairings and other aerodynamic features that earlier suspension bridge designers hadn’t considered necessary. It served as a turning point for the entire field of bridge engineering. After the Tacoma Narrows failure, wind tunnel testing became standard practice for long-span bridge design worldwide. The 1950 bridge still stands today, now carrying westbound traffic on State Route 16.
The 2007 Expansion
By the early 2000s, a single bridge could no longer handle the traffic volume between Tacoma and the Kitsap Peninsula. A second suspension bridge was built parallel to and just south of the 1950 structure, opening in early 2007. The $849 million project added a new span with two general-purpose lanes and one HOV lane for eastbound traffic, plus a separated path for bicycles and pedestrians. The project also included seismic upgrades and a new deck for the older bridge, along with improvements to 2.4 miles of the surrounding highway.
Today the two bridges operate as a pair: the 1950 bridge handles westbound traffic and the 2007 bridge handles eastbound. The crossing is tolled in the eastbound direction only. With a Good To Go! pass, the toll for a standard two-axle vehicle is $4.50. Paying at a toll booth costs $5.50, and if you skip both options, a bill arrives in the mail for $6.50. Larger vehicles with more axles pay progressively higher rates, up to $13.50 for six or more axles with a pass.
The Legacy in Engineering and Physics
The 1940 collapse was filmed by Barney Elliott, a local camera shop owner, and by Farquharson himself. That footage became one of the most widely shown engineering case studies in history, used in physics and engineering courses to illustrate how forces interact with flexible structures. The wreckage of the original bridge still sits on the bottom of Puget Sound, where it has become an artificial reef and is listed on the National Register of Historic Places.
The disaster fundamentally changed how engineers think about wind. Before 1940, bridge designers focused almost entirely on the static force of wind pushing against a structure. The Tacoma Narrows collapse proved that the dynamic interaction between wind and a flexible structure could be far more dangerous. Every major suspension bridge built since, from the Verrazano-Narrows to Japan’s Akashi Kaikyo, has undergone extensive aerodynamic testing as a direct result of what happened on that November morning in Washington State.