Evergreen Bridge Opens: World's Longest Floating Span

The longest floating bridge ever built opened to traffic on August 28, 1963, connecting Seattle to the affluent suburb of Medina across the deep, wide expanse of Lake Washington. The Evergreen Point Bridge, officially the Governor Albert D. Rosellini Bridge, stretched 7,578 feet across a lake too deep for conventional bridge pilings, a feat of engineering that relied on 33 hollow concrete pontoons anchored to the lake floor by steel cables. Lake Washington presented a unique engineering challenge. The lake sits in a glacially carved trough with soft sediment floors dropping to depths of 200 feet, far too deep and unstable for the pile-driven foundations that support most bridges. The solution, pioneered by engineer Homer Hadley for the nearby Lacey V. Murrow Bridge in 1940, was to float the bridge on concrete pontoons, essentially hollow boxes that displaced enough water to support the roadway above. The Evergreen Point Bridge refined this approach with larger pontoons and a higher deck to accommodate boat traffic. Construction began in 1960 and employed a workforce that had to contend with wind, waves, and the logistical complexity of building on open water. The pontoons were cast on shore, towed into position, and sunk to their operating draft by flooding internal chambers with water. Steel anchoring cables held them in place against wind and current. The bridge carried four lanes of traffic with no shoulders, a design that would become increasingly inadequate as Seattle's eastside suburbs exploded in population through the tech boom of the 1980s and 1990s. The original Evergreen Point Bridge served for over 53 years before being replaced by a new, wider floating bridge that opened in 2016, itself the longest floating bridge in the world at 7,710 feet. The old bridge was demolished, but its legacy shaped the development of the entire Seattle metropolitan area by making the eastside communities of Medina, Bellevue, Kirkland, and Redmond viable commuter suburbs. Microsoft, Amazon's early operations, and dozens of tech companies established themselves on the east side of the lake, in large part because a floating bridge made the commute possible.