Annual inspection of 520 bridge shows no new damage

While crews inspected the aging 520 bridge on Saturday, state transportation officials gave tours pointing out its deficiencies and presented a new emergency plan in case of a "catastrophic failure."

Local and state politicians, transit representatives and media attended the tour during the inspections, which will keep the bridge closed until 5 a.m. Monday.

No new damage had been found as of Saturday, said transportation spokeswoman Suanne Pelley.

Winter is the most dangerous time for the bridge because of the risk from windstorms, and the inspection is scheduled now so that problems can be fixed before then, said Archie Allen, bridge superintendent with the state transportation department. In addition to this weekend's annual inspection, smaller checks are conducted the second Thursday of each month.

Heavy storms, particularly the Inaugural Day storm of 1993, caused cracks in the pontoons, said Rick Roddan, assistant bridge superintendent. Those cracks are repaired now, and crews monitor for signs of new damage.

If there were catastrophic storm damage to the bridge, the emergency plan released Saturday would guide the coordination of communications with city transit agencies, businesses and emergency responders, and it would establish traffic detours.

The plan outlines some traffic alternatives. One scenario calls for a car-pool lane to be established in both directions of I-90 between Seattle and Bellevue within one month of the 520 bridge's failure. More options are listed in the event the bridge were closed for more than six months.

The state Transportation Department is making a surplus of modern pontoons in case of an emergency. Replacement pontoons on hand could speed construction of the new bridge, and they also could serve as replacement pontoons for the current bridge.

But the only permanent way to make the commute on 520 safer is to replace the bridge, transportation officials said.

Unlike the current bridge, its replacement, which officials hope to open in 2014, will be designed to withstand a "1,000-year-earthquake" and windstorms up to 92 miles per hour. Winds of 50 mph could be severe enough to cause the current bridge to sink, according to the project's Web site www.wsdot.wa.gov/Projects/SR520Bridge.

The new bridge also won't have a drawspan, which is the most maintenance-intensive part of the structure. Instead, the bridge span will be 72 feet high — the same height as the I-90 bridge that crosses Lake Washington to the south.

"I'll be happy to see the drawspan go," said Allen, the bridge superintendent. "If the bridge moves or the bridge floats, it requires a significant more amount of care than fixed bridges."

Other aspects of the new bridge discussed Saturday include quieter pavement, noise walls, bike lanes, shoulders and a wastewater-management system.

Sean Rose: 206-464-2292 or srose@seattletimes.com