Tacoma Narrows Bridge
The Tacoma Narrows Bridge is a pair of twin suspension bridges in the U.S. state of Washington, which carry State Route 16 (known as Primary State Highway 14 until 1964) across the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. Historically, the name "Tacoma Narrows Bridge" has applied to the original bridge nicknamed "Galloping Gertie" which opened in July 1940 and collapsed four months later, as well as the replacement of the original bridge which opened in 1950 and still stands today as the westbound lanes of the present-day twin bridge complex. The original Tacoma Narrows Bridge opened on July 1, 1940. It received its nickname "Galloping Gertie" due to the vertical movement of the deck observed by construction workers during windy conditions. The bridge collapsed into Puget Sound the morning of November 7, 1940, under high wind conditions. Engineering issues as well as the United States' involvement in World War II postponed plans to replace the bridge for several years until the replacement bridge was opened on October 14, 1950. By 1990, population growth and development on the Kitsap Peninsula caused traffic on the bridge to exceed its design capacity; as a result, in 1998 Washington voters approved a measure to support building a parallel bridge. After a series of protests and court battles, construction began in 2002 and the new bridge opened to carry eastbound traffic on July 15, 2007, while the 1950 bridge was reconfigured to carry westbound traffic. At the time of their construction, both the 1940 and 1950 bridges were the third-longest suspension bridges in the world in terms of main span length, behind the Golden Gate Bridge and George Washington Bridge. The 1950 and 2007 bridges are now the fifth-longest suspension bridge spans in the United States, and the 31st-longest in the world. Tolls were charged on the bridge for the entire four-month service life of the original span, as well as the first 15 years of the 1950 bridge. In 1965, the bridge's construction bonds plus interest were paid off, and the state ceased toll collection on the bridge. Over 40 years later, tolls were reinstated as part of the financing of the twin span, and are presently collected only from vehicles traveling eastbound.

Galloping Gertie
The desire for the construction of this bridge dates back to 1889 with a Northern Pacific Railway proposal for a trestle, but concerted efforts began in the mid-1920s. In 1937, the Washington State legislature created the Washington State Toll Bridge Authority and appropriated $5,000 to study the request by Tacoma and Pierce County for a bridge over the Narrows. The bridge was designed by Leon Moisseiff. The first Tacoma Narrows Bridge opened to traffic on July 1, 1940. Its main span collapsed into the Tacoma Narrows four months later on November 7, 1940, at 11:00 AM (Pacific time) due to a physical phenomenon known as aeroelastic flutter caused by a 67 kilometres per hour (42 mph) wind. The bridge collapse had lasting effects on science and engineering. In many undergraduate physics texts the event is presented as an example of elementary forced resonance with the wind providing an external periodic frequency that matched the natural structural frequency (even though the real cause of the bridge's failure was aeroelastic flutter ). Its failure also boosted research in the field of bridge aerodynamics/aeroelastics which have themselves influenced the designs of all the world's great long-span bridges built since 1940. No human life was lost in the collapse of the bridge. However, a small dog perished after it was abandoned in a car on the bridge by its owner, Leonard Coatsworth, and by another man, both of whom were bitten by the terrified dog when they attempted to remove it. The collapse of the bridge was recorded on 16mm film by Barney Elliott, owner of a local camera shop, and shows Leonard Coatsworth leaving the bridge after exiting his car. In 1998, The Tacoma Narrows Bridge Collapse was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant." This footage is still shown to engineering, architecture, and physics students as a cautionary tale. Dismantling of the towers and side spans—which survived the collapse of the main span but were damaged beyond repair—began shortly after the collapse and continued into May 1943. The United States' participation in World War II as well as engineering and finance issues delayed plans to replace the bridge.

Westbound bridge
The current westbound bridge was designed and rebuilt with open trusses, stiffening struts and openings in the roadway to let wind through. It opened on October 14, 1950, and is 5,979 feet (1822 m) long — 40 feet (12 m) longer than the first bridge, Galloping Gertie. Local residents nicknamed the new bridge Sturdy Gertie, as the oscillations that plagued the previous design had been eliminated. This bridge along with its new parallel eastbound bridge are currently the fifth-longest suspension bridges in the United States. When built, the westbound bridge was the third- longest suspension bridge span in the world. Like other modern suspension bridges, the westbound bridge was built with steel plates that feature sharp entry edges rather than the flat plate sides used in the original Tacoma Narrows Bridge (see the suspension bridge article for an example). The bridge was designed to handle 60,000 vehicles a day. It carried both westbound and eastbound traffic until the eastbound bridge opened on July 15, 2007.

Eastbound bridge
In 1998, voters in several Washington counties approved an advisory measure to create a second Narrows span. Construction of the new span, which carries eastbound traffic parallel to the current bridge, began on October 4, 2002, and was completed in July 2007. The Washington State Department of Transportation collects a toll before entering the eastbound span, at $2.75 for Good To Go! account holders with in-vehicle transponders, and a $4.00 toll (a more than 45% upcharge) for cash/ credit card customers. The existing span had been toll-free since 1965. The new bridge marks the first installation of the new Good To Go! electronic toll collection system.

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