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| Washington State Floating Bridges (was:Re: North and South Channel swing Bridges) (271813) | |||
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Washington State Floating Bridges (was:Re: North and South Channel swing Bridges) |
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Posted by WillD on Sun Jun 25 21:20:53 2006, in response to Re: North and South Channel swing Bridges, posted by Edwards! on Sun Jun 25 15:40:59 2006. There are four floating bridges in Washington State, two on I-90, the Lacy V. Murrow bridge, and one apiece on SR 520, the Evergreen Point floating bridge, and on SR 104, the Hood Canal bridge. 520 and I-90 both cross the deep and fairly narrow Lake Washington, and 104 crosses the Hood Canal, a deep fjord-like body of water just north of Bangor, WA. 520 crosses from roughly Seattle's U-district over to just south of Kirkland, while I-90 starts around the SODO area, tunnels under the Mt Baker neighborhood, and then crosses to Mercer Island, where a fixed span then carries it to just south of Bellevue.The southernmost span of I-90's Lacy Murrow memorial bridge was the first floating bridge WSDOT built, back in 1940 for what was then US 10. It was a four lane bridge with toll facilities on the Seattle side, and lead a fairly mundane life until the 1990s. In 1989 a parallel crossing, the Homer M. Hadley Memorial Bridge (named for the designer of the first I-90 bridge) opened to alleviate traffic on the original span. This turned out to be fortuitous since in 1990 a worker on the original span left a valve on one of the pontoons open and part of the bridge sank. The newly completed bridge served double-duty as an unplanned replacement while the original crossing was fixed. By 1993 the original bridge was rebuilt with some of the original components, and was reopened to traffic. Today the I-90 crossing has had its tolls removed and accomodates 3 lanes in each direction, with three other reversable HOV lanes for peak hour travel. With 6 lanes on it the new I-90 bridge is the widest floating bridge in the world. The next bridge completed by WSDOT was the Hood Canal bridge in 1961. This is the only floating bridge across a tidal waterway in Washington, as well as possibly the US and the world. It has a central drawbridge which opens to allow missile submarines from the US Naval base at Bangor Washington pass, and has just one lane in each direction. Staying true to WSDOT's ineptitude with bridges the western end of the bridge sank in a storm in 1979. This occasioned Washington State Ferries to reinstate the ferry service they'd eliminated just 20 years before, but by 1982 the bridge was rebuilt and open to traffic. Today the Hood Canal Floating bridge still has just two lanes, and frequently opens for storms, to alleviate the kind of stress on the structure which sank it in 1979. The final floating bridge is the Evergreen Point bridge, which was completed in 1963. This is the longest floating bridge in the world, and thusfar has been Washington's least troublesome crossing (if you ignore the daily traffic jams). 520 has just four lanes and is a daily nightmare for tens of thousands of commuters from Kirkland, Bellevue, Redmond, and Eastside points north and east of there. There's talk of building a parallel crossing, a fifth bridge, but nobody seems to be able to decide how it should be done, so nothing happens and everyone just sits in traffic. I do remember when I was a kid being horrified when a control circuit in the drawbridge shorted and opened the bridge with cars on it. Several people in cars were crushed when the multi-ton span came up onto the road deck, but I think that's the worst incident that the Evergreen Point Bridge has had. I believe every floating bridge has a lifting drawbridge section in the middle for vessels too large to use the overpasses at either end. I believe it mostly consists of a section of road which is just a caisson with its water pumped out until it floats, then is hydraulically jacked up onto the bridge behind it and rolled onto the floating bridge. The one link to the Evergreen Point bridge shows this to good effect. I know 520 and 104 have them, the latter since it's on a navigable waterway and acts as a chokepoint for a naval base, but I'm not sure about the two I-90 crossings. It seems that the new crossing was built without a drawbridge and when the old crossing was rebuilt the drawbridge was eliminated. |
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