Evergreen Point At Heart of I-912 Debate
By: Peggy Anderson
The King County Journal
October 21, 2005
Fixing the Evergreen Point floating bridge and the Alaskan Way Viaduct are at the center of the debate over Initiative 912, which would repeal the gas-tax increase imposed by the Legislature this year to pay for those and other projects.
But just how dire is the situation?
Together, the two spans carry 225,000 vehicles daily through the congested heart of the Puget Sound region -- 115,000 on the bridge that has taken State Route 520 commuters across Lake Washington since 1963, and 110,000 on the 50-year-old viaduct that carries State Route 99 above Seattle's downtown waterfront for 2.2 miles. Both were designed to carry about 65,000 vehicles per day.
``Sheer volume and location put them at the top of the list'' of state Department of Transportation concerns, agency spokeswoman Linda Mullen said.
As Gov. Christine Gregoire put it recently: ``These are our levees. And the earthquake is our hurricane.''
Concrete is porous. Air and water seep through and, over time, expose the internal steel skeletons of aging structures like the viaduct and the floating bridge.
The steel speeds the process, expanding when the weather is warm and contracting when it's cold. This flexing stresses the concrete and triggers a phenomenon called ``spalling.''
``Old concrete crumbles and pops as the steel expands,'' exposing the metal and accelerating the rust process, said Patrick Moylan, state Department of Transportation maintenance and operations manager.
And then there are outside factors such as earthquakes.
Dave Dye, who administers big Puget Sound-area projects for the DOT, said predicting the next big earthquake is speculative at best.
``But we do know we are overdue for an earthquake, and we know that neither of these structures will fare very well,'' Dye said.
Along with the lives that might be lost, a downed viaduct would add a full lane of traffic to Interstate 5 at rush hour -- and increase five hours of daily congestion to 14, he said. Losing the bridge would shift its passengers to the Interstate 90 bridge a few miles to the south.
The viaduct has been intensely studied since the 2001 Nisqually quake, when officials discovered the structure had shifted 4 inches from the original design. It's not clear how much of the shifting was caused by the 6.8-magnitude earthquake.
``We really didn't look at it till after the quake,'' Mullen said during a recent walk beneath the structure that towers between downtown and the waterfront.
Experts say there's a 1 in 20 chance that the next 10 years will bring an earthquake strong enough to make the soaring roadway unusable.
Since 2001, the viaduct has been subject to Nisqually-related patching -- epoxy injections to fill in for spalled concrete, steel ``knee braces'' to strengthen creaky uprights, carbon-graphite fiber wraps to strengthen crossbeams. About 30 6-inch plastic gauges record the slightest movement along worrisome fissures.
Two crossbeams linking pairs of the 181 big uprights are secured by ``post-tensioning rods'' that essentially squeeze fragile concrete together.
Similar systems hold the Evergreen Point bridge together. Sixteen post-tensioning cables in orange PVC pipe run the length of the bridge's two floating sections. They cinch up the 33 pontoons, tightening up the cracks that crisscross the pontoons and stripe the barriers on either side of the roadway.
Inside the pontoons, repaired cracks show as dark lines about 3 inches wide. Some of the dark bands have a bubbly white pattern down the middle, a sign water's getting in anyway.
``The people driving don't realize we are making constant repairs,'' said Rick Rodda, assistant superintendent of the bridge maintenance office, on a recent sunny day as cars and trucks zipped across the lake.
The bridge's floating halves are separated by a draw span for vessels that must be raised frequently to ease pressure from high winds. Sometimes the bridge is closed because waves are washing across it, making driving hazardous.
The draw span itself is a weak point on the aging bridge.
Chief DOT Engineer John Milton worries about wind and waves as well as earthquakes.
``We believe the bridge has a 20-year life span left. That's assuming no earthquakes and no bad storms,'' Milton said. But he figures the region is overdue for a battering storm after a dozen years of relative calm.
``As an engineer, I feel it's at a point we should be concerned,'' Milton said. ``We're taking risks already. I don't like relying on nature not to do something.''
Two of the state's three floating bridges have sunk over the years -- the western half of the Hood Canal Bridge during a 1979 storm, and half of the Interstate-90 bridge across Lake Washington in the 1990 Thanksgiving storm.
Those events helped spur modifications to the Evergreen Point bridge.
Waterproof hatches were added after the 1990 storm. An alarm system alerts tenders whenever 6 inches of water accumulates in any of the pontoons. A generator now ensures power to the draw span.
``It sits 6 or 7 inches lower in the water than when it was built'' because of the weight of the improvements, Rodda said.
A concrete wave-deflector was replaced with a metal one to lighten the load. Steel catwalks inside the 360-foot-long pontoons were replaced with fiberglass.
``We are at the max,'' Milton said. ``We can't add anything out here without taking away something else.''
