Longest floating bridge

The longest floating bridge is the Evergreen Point Floating Bridge (officially the Governor Albert D. Rosellini Bridge), which connects Seattle to the suburb of Bellvue, Washington across Lake Washington. The pontoon-supported section of the bridge measures 2,349.55 m (7,708.49 ft) from end to end. The bridge was constructed between 2012 and 2016 to replace an earlier pontoon bridge, and opened to the public on 11 April 2015.

A floating bridge, or pontoon bridge, is one in which the spans are supported by floats rather than supports that reach to the bottom of the lake, sea or river. These floats can be simple boats – as is the case with rapidly-assembled military bridges – or massive watertight concrete boxes, as used for permanent structures. The Evergreen Point Bridge has 77 pontoons, each anchored both to its neighbours and to a series of massive weighted anchors by sturdy steel cables.

All the major bridges over Lake Washington use floating pontoons to support their decks, an unusual feature in permanent bridge designs. The reason for this is the geography of the area. Lake Washington is 214 ft (65 m) deep at its deepest point, and the lakebed consists of another roughly 200 ft (60 m) of soft mud sitting atop the bedrock. As a consequence, it is not feasible to sink pilings to support bridge piers. Meanwhile, crossing the lake in a single span would require the construction of a colossal bridge whose cost would be astronomical and whose towers would dwarf every other structure in the city.

The 2016 Evergreen Point Bridge was built to replace an earlier pontoon structure in the same location. This bridge, which was slightly shorter than the new one, was constructed in 1963.