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This Century's Top Ten Construction Projects


This Century's Top Ten Construction Projects
December 9, 1999

Lake Washington Bridge still wowing visitors

Dates: 1938-1940
Costs: $8 million
Contractor: Traylor Bros.
Amazing Fact: The shortest distance between Seattle and Mercer Island is about half as long as the Lake Washington Floating Bridge

When Homer M. Hadley first presented the idea of a floating concrete bridge spanning Lake Washington, people thought the idea was all wet.

But from his experience working in a shipyard during World War I, Hadley knew that concrete could be made to float. And building a floating bridge would be easier than trying to place piers in water 200 feet deep, with another 100 feet of soft clay on the lake bottom.

For 50 years, Hadley's idea kept cars afloat on Interstate 90.

In 1930, the city of Seattle and King County granted a franchise to the Seattle Toll Bridge Co. to build the Seward Park span, but financiers failed to step forward with bridge funds, and the plan fell through.

Lake Washington Bridge opening
Celebrants gathered for the bridge opening on July 2, 1940. One DJC reader who voted for the project said that the floating bridge is an attraction that sets "visitors abuzz, even after they leave. . ."
King County took over the project in 1935 with plans to build a steel truss cantilever from Seward Park for an estimated $3.5 million. Still, financing was a problem.

The state created the Washington Toll Bridge Authority to get federal grant money. The toll bridge authority was charged with locating, designing, financing and building both the Lake Washington and the Tacoma Narrows bridges.

In June of 1937 Lacey V. Murrow, a member of the toll authority and director of the state Highway Department, listened to Hadley's plan for a bridge made of concrete pontoons. The idea stuck.

Pontoons seemed ideal. Concrete would be less expensive, and a seven-foot immersion in the water would be enough to stabilize the bridge during rough water.

Murrow was satisfied that enough motorists would use the bridge, at 25 cents per car, to repay the revenue bonds to finance more than half of the $8 million it would cost to build it. A $3.7 million federal grant would pay for the rest.

Work began on the Lake Washington Floating Bridge on Dec. 31, 1938. For the next 18 months, more than 3,000 men were employed on the bridge construction.

The four-lane concrete highway consisted of 25 floating pontoons bolted together end-to-end and attached to fixed approach spans.

The bridge was anchored with steel cables to resist wind and waves, and hydraulic jacks to let out or take up the slack.

It was the first floating draw span in the world, with a 200-foot section designed to allow vessels to pass through. Two 75-horsepower motors were used to open the span in 90 seconds.

The bridge opened on July 2, 1940 as a crowd of 2,000 watched the christening of the 6,620-foot floating span.

Fifty years after it was built, water from a heavy rainstorm filled the pontoons and the floating bridge sank into Lake Washington on Nov. 25, 1990. Right away, efforts began to replace it with $88 million in emergency highway funds.


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