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When a bridge is being designed there are several factors to consider including the weight it must hold, the weather it must endure, the terrain, the building materials to be used, and the cost.
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A beam bridge is supported by one or more beams. An example of a beam bridge is southern Louisiana's Lake Pontchartrain Causeway bridge that spans 23.83 miles. It is the world's longest.
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A truss bridge is supported by a truss that bears the load of the bridge and everything that crosses it.
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A cantilever bridge is built with two sections that are each supported on one side and meet in the middle. The largest cantilever bridge in the world is the Quebec Bridge in Canada, at 1801 feet.
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An arch bridge has an abutment (substructure) at each end that takes the weight. The largest arch bridge is Chaotianmen Bridge in Chongqing, China, at 5,712 feet long.
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A suspension bridge is suspended by cables hung from towers. The towers are deeply rooted into the ground or underwater floor by caissons or cofferdams.
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A cable-stayed bridge is held up by cables but towers are higher than suspension bridges. The Russky Bridge in Russia is the longest cable-stayed bridge in the world.
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Footbridges are built for people to cross on foot. These usually do not cover very long spans, but make it possible to cross rivers, streams, roadways, or other gaps.
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The world's oldest bridge still being used is the stone-segment arched Zhaozhou Bridge in China that was built in 605 A.D.
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The Inca civilization in South America is known for the rope suspension bridges they built to enable crossing steep ravines and gorges in the jungle.
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The Akashi Kaikyo Bridge in Kobe, Japan spans a distance of 6529 feet. When it opened for use in 1998 it became the longest suspension bridge in the world.
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The busiest bridge is the George Washington Bridge that connects New Jersey's Bergen County to New York City. More than 102 million vehicles use it each year. It is a double decker bridge.
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The Siosepol Bridge in Esfahan, Iran was built during the Safavid dynasty between 1599 and 1602. It has 33 arches spanning 976.9 feet.
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Sometimes bridges fail due to inadequate maintenance, poor design, structural failure due to unforeseen circumstances, or even earthquake or other natural disasters.
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The Golden Gate Bridge in San Francisco is 8981 feet long and incorporates 80,000 miles of cable. It is one of the most famous bridges in the world.
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