Advertising

Thursday, March 4, 1999 - Page updated at 12:00 AM

E-mail article     Print

Broken-Down 520 Bridge On Last Legs? -- But No Plans Exist To Replace Or Upgrade It

Seattle Times Eastside Bureau

The Evergreen Point Floating Bridge - long the poster child for the region's worsening traffic congestion - has become a broken-down mid-lifer with no life-insurance policy.

The critical condition of the bridge was never more apparent than yesterday morning when thousands of commuters were gridlocked after the bridge broke under high winds.

And despite frantic efforts to repair the span no later than tomorrow's commute, long-term plans to enhance the bridge, or to add additional travel routes over Lake Washington, are stalled by politics and lack of money.

"The bridge is getting old - it's basically a bunch of boats strung together, and they're getting old and creaky," said state Senate Republican Leader Dan McDonald, an engineer whose Yarrow Point home sits near the bridge on the lake's eastern shore.

Built 36 years ago to carry state Highway 520 across Lake Washington, the bridge doesn't meet today's standards - and barely meets yesterday's. It has broken several times, and engineers put its life expectancy at 20 to 25 more years - barring another huge windstorm.

Modern bridges are supposed to withstand 90-mph winds. Yesterday, a mechanical assembly on the Evergreen's drawspan rollers broke when winds hit 45 to 50 mph. In 1993, its pontoons cracked with gusts of 70.

If winds ever roar faster than that, "it's kind of a crapshoot," said Chuck Ruth, a state bridge-design engineer.

Since last summer, crews have been keeping the bridge viable

with the structural equivalent of bubble gum and duct tape: They inject a gummy sealant into cracks in pontoons, then wrap them in steel cables for reinforcement. Those efforts have barely kept the bridge above 1963 standards - able to withstand sustained winds of 58 mph.

That won't work forever.

"Time has kind of had an effect on that, just like on us," Ruth said. "We could go through a certain intensity of storm several years back. The same storm now, we get leakage."

Chief bridge engineer Jerry Weigel said his crews have abandoned efforts to bring the 520 bridge up to current wind standards - 92 mph, the kind of wind expected once every 100 years - noting the work is too expensive to justify.

Washington's three floating-bridge corridors were considered an efficient and innovative way to span the broad waterways surrounding Puget Sound, but each has had its troubles: The Hood Canal bridge collapsed during a windstorm in 1979, one leg of the Interstate 90 bridge sank when pontoons flooded during a heavy storm in 1990, and the Evergreen Point bridge has endured chronic storm damage.

Yesterday's earliest commuters faced fierce winds, with gusts up to 73 mph, as they crossed the lake.

"It was like driving through a carwash over the entire span," said one Kirkland resident. "Zero visibility."

Traffic was stopped about 6 a.m. so the drawspans could be opened - a common practice to relieve wind stress on the bridge. But as the spans were raised and the center pontoons retracted, a heavy metal plate that holds guide rollers and a roller assembly snapped.

Without the rollers, it was impossible to guide the drawspan sections back into place.

To repair the damage, a 6,000-pound beam had to be moved to reach the broken assembly. And the resulting traffic disruption further slowed repairs. Replacement parts were stored in a maintenance shop on the Eastside, but the damaged section of the bridge was on the west side of the gap; parts had to be trucked around the lake.

This morning, Pat Moylan, bridge superintendent, estimated repairs will cost about $30,000. In addition to fixing the vertical roller assemblies, crews must replace stripped bolts and a support beam because the axle supporting the guide rollers was broken. Also damaged was the center lock system, two hooks that hold the center pontoons together.

Drivers coped with the bridge closure today, said James Jackson, DOT traffic systems specialist. DOT traffic cameras on I-90 showed some slowdowns throughout the morning, but nothing extraordinary.

"When you look at the traffic going across the floating bridges on Lake Washington, about 100,000 cars a day cross each one, so it's a tremendous, significant lifeline for the community," said retired state bridge engineer Myint Lwin.

In a bit of irony, the bridge broke the same day a regional task force gathered to examine the growing traffic burden on 520. A possible two-day shutdown of the bridge brought the group's challenge into sharp focus.

After a year of debate, the task force yesterday narrowed its options for commuter relief: Run rail transit across 520 or I-90; add more lanes to 520; build a tubelike floating tunnel tethered to the lake bottom; or run passenger and bus ferries from downtown Kirkland to the University of Washington or Sand Point.

No longer considered viable are proposals to add a third bridge, north of 520, crossing the lake from Sand Point to Kirkland or Juanita. A cursory study estimated 1,500 homes and businesses would have to be demolished to build a new bridge - in neighborhoods with substantial political clout to protest.

Meanwhile, state engineers are warning that the 520 bridge will need to be replaced no matter what other transit solutions are found. But cost estimates for that project run to $1 billion, equivalent to a third of the money approved last year for all statewide highway improvement projects as part of Referendum 49.

Aubrey Davis, a state Department of Transportation commissioner and former mayor of Mercer Island, said every solution seems to pose a new set of problems. The second Mercer Island bridge, he noted, opened less than 10 years ago and already is routinely clogged.

If a new bridge is pursued, it would probably look a lot like the current one - based on World War I military pontoon technology that has been Washington's long-span bridge of choice since the 1940s.

Unlike the suspended ribbons of steel that carry cars over San Francisco Bay and the Tacoma Narrows, the Lake Washington bridges are "floaters" - built over lake beds too wide and deep to handle a rigid structure. Also unlike suspension bridges, the 520 bridge sloshes around in the water, where moisture and waves deteriorate its concrete pontoons, and age has worn the moving parts, making it more vulnerable to windstorms.

"Wind for floating bridges is not good, said Weigel, the chief bridge engineer. "I've heard a couple people say, when they hear it start to howl, they worry."

-------------------------------------------------------.

520 by the numbers

Total shore-to-shore distance: 12,404 feet.

Length of floating portion: 7,578 feet.

Drawspan opening: 200 feet.

What's under the pavement? 33 concrete pontoons.

What holds it in place? 62 anchors.

Number of vehicles crossed per day, 1964: 17,400.

Number of vehicles crossed per day, 1997: 102,000.

Copyright (c) 1999 Seattle Times Company, All Rights Reserved.

advertising


Get home delivery today!

Advertising

Advertising