Transportation structures wear out. Roads get potholed, signs fade, viaducts crack and bridges sink. It is a fact of life in the Pacific Northwest where the sky falls and the earth shakes.
That said, the SR 520 project team is working hard to make sure the SR 520 Floating Bridge does not become the fourth state bridge (the third floating bridge) to take the plunge.
The following are a couple of unfortunate examples the region has hopefully learned from and will use to prevent a similar future SR 520 bridge scenario.
The original Lacey V. Murrow I-90 Floating Bridge was constructed of reinforced concrete and opened in July 1940. After 50 years of service, it was closed to traffic for modern upgrades. Unfortunately, while undergoing renovation, its pontoons took in tremendous amounts of water during a long rainstorm over Thanksgiving weekend in 1990 and the middle of the bridge sank to the floor of Lake Washington.
Creating quite the spectacle, eight of the bridge’s pontoons rolled, bobbed around all day and finally sank at dusk on November 25, 1990. It cast Seattle into the national spotlight and prompted a region-wide movement to name the new “bobbing” bridge. Drowning Doris, the U.S.S. Murrow, the Sub-Mercer-ble Island Bridge were among the best of them.
The surviving pontoons suffered major damages and were considered structurally unsound for reuse in a major highway system. Cross-lake travel roared to a halt as motorists resorted to traversing the perpetually plugged SR 520 bridge or driving clear around the lake. Citizens quipped, “Welcome to Seattle – the most livable, least accessible city” and “Hey call our travel agent – book us a trip across the lake, will ya?” People took the loss in stride, but it wasn’t a fun time for cross-lake commuters.
The west half of the Hood Canal Bridge suffered a similar fate. It also sank – years before – on February 13, 1979 during a storm packing 120 mph gusts and 85 mph sustained winds. It was 18 years old at the time. Three years after its comparatively quiet sinking, the $143,000,000 western half was rebuilt and the bridge reopened in 1982. Tolls were lifted in 1985.
The Hood Canal Bridge was first opened in 1961, and in its unique marine environment, experiences tide swings of 16.5 feet. It is the only floating bridge in Washington State built over tidal waters.