The Washington State Department of Transportation said its own mistakes in the design of the new Highway 520 floating bridge will costs tens of millions of dollars and delay construction, according to reports.
Inspections found that cracks in the bridge's pontoons grew over the winter as a result of design problems caused by the department, according to the Seattle Times.
Transportation Secretary Paula Hammond said the problems will mean the department will miss a December 2014 deadline for opening the bridge connecting Seattle and Bellevue, Wash. across Lake Washington, according to the newspaper.
Officials have put the total cost at around $4.6 billion for the floating bridge project, which had been expected to open to traffic by December 2014.
The most recent plan included $800 million to $900 million of Garvee bonds, $112 million of toll revenue bonds and $550 million of triple-pledge bonds.
Floating bridges are typically made of large, watertight concrete pontoons connected end to end.
One of the bridge's pontoons — 28 feet tall, 75 feet wide, and 360 feet long — weighs more than 11,000 tons, according to the DOT.
The pontoons are built on land near the lake and then floated to the bridge site and held in place by steel cables connected to anchors in the lake bed.
Washington has more floating bridges than anywhere in the world, and the four longest and heaviest floating bridges — the current 520 bridge, the two Interstate 90 bridges across Lake Washington, and the State Route 104 Hood Canal Bridge.
