(The toll for an automobile would go from $6 to $8, collected only from northbound traffic the Golden Gate was the first major toll bridge to charge tolls only one way, thereby allowing traffic to flow freely in at least the other direction.) The toll hike was expected to increase revenue by $138 million, which the district had initially planned to use for seismic reinforcement of the bridge, the installation of a moveable barrier to allow the six-lane roadway to be divided unequally during rush hours, and improvements in ferry and bus service. By closing the trusswork in this way, the bridge deck was made significantly stiffer, especially against being twisted.Ī debate about adding any kind of suicide prevention system to the bridge had raged for decades, but it came to a potential resolution in 2014, when the region’s Metropolitan Transportation Commission pushed for the funding of a $66 million project to either build a high fence atop the railing or extend a safety net out beyond the edge of the bridge, to be paid for in part by a planned toll increase. To address such issues, an additional horizontal truss was added that connected the bottoms of the two vertical ones of the Golden Gate. In 1951, wind caused the bridge deck to sway and roll, and there was concern that these motions could become unstable and develop into the kind of twisting that destroyed the Tacoma Narrows Bridge. ![]() Strong winds can also cause vehicles on the bridge to become difficult to control, and can blow over trucks with large, exposed side panels. When the Tacoma Narrows Bridge was brought down in 1940 by a 40 mile-per-hour (64 kilometer-per-hour) wind that induced vertical and twisting oscillations along its entire length, there was cause for concern, because winds through the Golden Gate strait can gust to 75 miles (121 kilometers) per hour. A certain amount of vertical displacement was also expected, but not to the extent that traveling waves were observed to develop along the length of the roadway. The deck was designed to move almost 30 feet (9 meters) laterally in a crosswind, a distortion that was easily seen by sighting along a line connecting the bridge’s two towers. The truss arrangement proved to be inadequate in preventing the roadway from excessive movement. The bridge was designed and built with a pair of vertical stiffening trusses connected by a horizontal one incorporated into the deck, which carried six traffic lanes and two wide sidewalks. ![]() The Golden Gate Bridge fell into this category. As the design of any bridge is basically a theoretical hypothesis until it is built and tested by traffic and the elements, bridges designed and constructed in the 1930s tended to be susceptible to movement in strong winds, an old phenomenon that did not manifest itself anew until the second half of the decade. In other words, the bridge deck became lighter and less stiff and less constrained. However, beginning early in the 20th century, suspension bridge design trended toward a sleek aesthetic combined with a narrow structure spanning a greater distance. His Brooklyn Bridge epitomized the application of this formula. ![]() John Roebling, the engineer of the Brooklyn Bridge, understood this problem in the middle of the 19th century, when wind was destroying suspension bridges, and his design imperative for a bridge to sit steady in the wind was that its deck be sufficiently stiff by having substantial weight, longitudinal trusses, and diagonal stay cables. This layout naturally meant the decks were lighter, which in turn led them to be more flexible, which in time manifested itself as excessive motion in the wind. However, as suspension bridges began also to be built in less populated areas, where traffic consisted almost exclusively of cars and trucks, trussless decks carried only two lanes of traffic plus a very narrow sidewalk or two. The resulting wide bridge decks were necessarily heavy, and this feature even in the absence of the stiffening trusses made the roadways very stable in the wind. Around large cities, this trend led to bridges with three or four traffic lanes in each direction plus tracks for commuter trains. This aesthetic imperative worked fine for bridges designed to carry multiple lanes of vehicular traffic in addition to railroad trains and pedestrians. The bridge was designed at a time when the state-of-the-art in bridge engineering was to make the roadway of a suspension bridge look as slender as possible. The Golden Gate Bridge has undergone more significant structural and behavioral changes.
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