The Tacoma Narrows Bridge (called "Galloping Gertie") opened to traffic on July 1, 1940. It collapsed on November 7, 1940, approximately four months after it opened. Its collapse was caused by a 42 mph wind. Initially, it vibrated in a transverse mode with a frequency of about 36 Hz and an amplitude of 1.5 ft. These transverse vibrations had occurred at other times during the four months it had been open. Later, a new torsional (twisting) vibration with a frequency of about 14 Hz began. This new vibration caused the collapse of the bridge. The original bridge design involved suspended plates that caught the wind, rather than allowing it to pass through. Click on the link below to see a short movie of the torsional and the transverse vibrational modes.