The State Route 520 Floating Bridge in Seattle, Washington
Home to around 3.5 million people, the metropolitan area of Seattle is divided by Lake Washington and the SR 520 transports 115,000 vehicles across Lake Washington on a daily basis. At depths reaching 61 m  a suspension bridge would require a bridge tower of over 183 m; thus a floating bridge is necessary. Constructed in 1963, this bridge however is now approaching the end of its lifespan and will be replaced by an even longer and wider floating bridge by 2014.
This paper will investigate why the bridge must be replaced, the past and current reasons for selecting a floating bridge to cross Lake Washington, what it takes to make a concrete bridge float, and how the new bridge will vary from the existing bridge.
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