Lacey V. Murrow Memorial Bridge
 |
Lacey V. Murrow Memorial Bridge (right), looking east toward Mercer Island |
The
Lacey V. Murrow Memorial Bridge is a floating bridge that carries the eastbound lanes of
Interstate 90 across
Lake Washington from
Seattle to
Mercer Island, Washington. It is the second longest
floating bridge in the world, at 6,620 feet (2,019 meters); the longest, incidentally, is the
Evergreen Point Floating Bridge just a few miles to the north, built 23 years later.
The bridge was the brainchild of George Washington Lightfoot, who came to be called the "father of the bridge". Lightfoot began campaigning for the bridge in 1930, enlisting the support of Miller Freeman. The original two-way, four-lane
toll bridge was designed by the engineer Homer Hadley (1885-1967) and constructed of reinforced concrete in
1940. Tolls were removed in 1946. It sank in a storm on
November 25,
1990, while it was undergoing refurbishing & repair. The current bridge was built in
1993.
Formerly known as the "Lake Washington Floating Bridge", the original bridge included a movable span that could be retracted into a pocket in the center of the fixed span to permit large boats to pass. This design resulted in a roadway "bulge" that required vehicles to swerve twice across polished steel joints as they passed the bulge. A "
reversible lane" system, indicated by lighted overhead
lane control signals with arrow and 'X' signs, compounded the hazard by putting one lane of traffic on the "wrong" side of the bulge at different times of day in an effort to alleviate rush-hour traffic into or out of Seattle. There were many serious collisions on the bridge. The problems grew worse as the traffic load increased over the years and far outstripped the designed capacity. Renovation or replacement were essential and a parallel bridge, the
Homer M. Hadley Memorial Bridge, was completed in
1989.
The sinking of the original bridge was an example of human errors and decisions compounding to lead to disaster. The process started because the bridge needed
resurfacing and was to be widened by means of cantilevered additions. The
Washington State Department of Transportation (WSDOT) decided to use
hydrodemolition (
high-pressure water) to remove unwanted material. Water from this hydrodemolition was considered contaminated under
environmental law and could not be allowed to flow into Lake Washington. Engineers then analyzed the
pontoons of the bridge, and realized that they were over-engineered and the water could be stored temporarily in the pontoons. The watertight doors for the pontoons were therefore removed. A large storm arose on
November 22,
23, and
24, 1990 (the
Thanksgiving holiday weekend). This filled some of the pontoons with
rain and lake water. On November 24, workers noticed that the bridge was about to sink, and started pumping out some of the pontoons. However, on
November 25, 850 meters of the bridge sank, ironically dumping the contaminated water into the lake along with tons of bridge material. The bridge sank when one pontoon filled and dragged the rest down because they were cabled together and there was no way to separate the sections under load. Fortunately, no one was hurt or killed, since the bridge was closed for renovation and the sinking took some time. All of the sinking was captured on film and shown on
live TV.
Precedents and lessons for the future
Ironically, WSDOT lost another floating bridge, the
Hood Canal Bridge, about a decade earlier under similar circumstances, and it is now known that another major floating bridge in Washington, the
Evergreen Point Floating Bridge, is under-engineered for local environmental conditions.
["WSDOT Projects: SR 520 - Bridge Replacement and HOV Project", Washington State Department of Transportation]Future Plans
When the second bridge was built parallel to the existing span, it included a set of two
HOV lanes, reversible to accommodate the flow of traffic between Seattle and the Eastside (westbound in the morning, eastbound in the evenings). Unfortunately, because
the lanes are reversible, this pushes all the HOV traffic going on one side (depending on what time it is) to the general purpose lanes. This has been a huge problem with the increasing amount of
congestion in Seattle, Mercer Island and Bellevue. WSDOT is assessing the situation presently, and are planning to convert the lanes to two-way traffic. Half of this project is funded, and the first phase is estimated completion in 2009.
*
Homer M. Hadley Memorial Bridge*
Bridge Camera, includes some weather information*
Report from engineering firm analyzing the sinking of the bridge*
History Link on the Bridge*
Department of Transportation Sinking photos
