Where is the world’s largest bridge?

The answer to this question rather depends on your definition.  There is no universally accepted definition of what constitutes the size of a bridge.  Generally, though, two types of measurement are considered when trying to determine which is the world’s largest bridge; the total distance between the two shores connected by the bridge, and the length of the main span between the two towers on the largest suspension bridges.

If the first definition is used, the largest bridge in the world is the Lake Pontchartrain Bridge just outside New Orleans, which connects the north and south shores of that lake – a total distance of nearly 24 miles.  Most record books tend to consider the largest bridges in the world to be suspension bridges, however, and by this measure, the world’s largest bridge is the Akashi-Kaikyo Bridge, in Japan, which has a central span of over six and a half thousand feet.

(http://en.wikipedia.org/wiki/Image:Akashi_Bridge.JPG)

Why is it an engineering marvel?

The Akashi-Kaikyo Bridge took twelve years to complete, and in order to build it, the engineers had to overcome a number of serious issues.  Not the least of these was the Kobe earthquake of 1995, which in addition to leveling the nearby city of Kobe and killing over six thousand people, moved the two towers then under construction further apart by nearly a meter.  Fortunately, the world’s largest bridge was designed to withstand massive seismic events, and the structure was mostly undamaged.  Building across one of the busiest sea lanes in Japan caused problems all its own, and to make matters worse, the straits in which the bridge is situated have some of the worst weather in the world, with hurricanes and heavy seas a constant problem.

http://www.pbs.org/wgbh/buildingbig/wonder/structure/akashi_kaikyo.html

Are there any larger bridges planned?

Although there are many large bridges under construction all around the world, few are expected to be longer than the largest bridges in the world currently.  A project to build a bridge connecting Sicily with the mainland of Italy would have been the largest bridge in the world, with a 2-mile main span.  However, this project was abandoned in late 2006 due to concerns over costs and safety.  Another contender for the title of largest bridge in the world is also unlikely ever to see the light of day:  the Bering Strait Bridge, which would connect Alaska with Siberia across the 50 miles that separate the USA from Russia across the frozen straits.  However, the immense technical challenges, cost, and sparse population of the two regions mean that this project is unlikely to get the green light in the foreseeable future.

http://en.wikipedia.org/wiki/Bering_Strait_bridge