Hadley’s Folly

A Floating Bridge Made of Concrete

“Imagine such a structure staggering and lurching in the grip of a real storm! Imagine what would happen to automobiles trying to cross it! But worst of all, imagine what would happen if the thing came apart!”
—The Seattle Times editor C.B. Blethen on the construction of a floating bridge[1]

Why a Floating Bridge?

Homer M. Hadley
Homer M. Hadley
“C.E. Andrew, the project engineer, claimed it would be impossible to build a conventional bridge anchored on piers between Mercer Island and the western lake shore due to the depth of the water, which exceeds 200 feet in places.
The soft, muddy bottom of Lake Washington would require piers at least 350 feet, he said, longer than those used for the San Francisco–Oakland Bay Bridge.”[2]

Lake Washington is a deep lake with a soft muddy bottom, this makes conventional bridge design completely impossible. Homer M. Hadley a structural engineer was the first to come up with a solution to the problem: a bridge that floats. At first he was laughed at, the idea was called “Hadle’s Folly” by investment bankers he attempted to obtain funds from. But then he took his idea straight to Lacy V. Murrow, State Highway Director, who loved it.

“Designed by the engineer Homer Hadley (1885–1967), the bridge floats on hollow concrete pontoons. This technology was highly innovative at the time.”


““If Seattle will stop arguing over what it wants and decide on something ... funds will be available,” [senator] Magnuson said. “There is no objection whatever in Washington, D.C., to a pontoon bridge.” It came down to a Seattle City Council vote – 5 in favor, 4 against. “Hadley’s Folly” or Murrow’s bridge, it would be built.”[4]

There was much controversy over bridging Lake Washington with a floating bridge. People had 2 main fears, that the bridge may sink in a storm,and that it would be an eyesore. There was much campaigning for and against the bridge and it was approved by the Seattle City Council by a very narrow margin.

The Bridge is Built

“Construction began on Jan. 3, 1939. The bridge – at the time the largest floating object ever built, and the only floating concrete bridge – would carry its first cars in 18 months.”[4]
The bridge was built using floating hollow concrete pontoons linked together by steel cable and anchored into the lake bed by large anchors. How does it work?

Page Works Cited

1.Boswell, Sharon and Lorraine McConaghy. “A bridge to the future.” 16 June 1996. The Seattle Times 1896-1996. 10 October 2009 <http://seattletimes.nwsource.com/special/centennial/june/bridge.html>. 2. Rothschild, Mary. “Why A Floating Bridge, Anyway? Depth Of Lake And Economics Dictated The Highway On Pontoons.” Seattle Post–Intelligencer 28 November 1990, Final ed.: A8. 3. Lange, Greg. “First automobile drives across Lake Washington Floating Bridge on June 5, 1940.” 14 Janurary 1999. HistoryLink.org: The Free Online Encyclopedia of Washington State History. 1 March 2010
4. Engstrom, John. “Our hearts sank Seattle's soul took the high road over a floating concrete bridge; [FINAL Edition].” Seattle Post–Intelligencer 20 December 1990: C8.