Semiannual inspection closes SR 99 Alaskan Way Viaduct this weekend

WSDOT tests automated viaduct closure system

WSDOT press release:

Crews will close the State Route 99 Alaskan Way Viaduct this weekend for its semiannual inspection and to test a new system that automatically closes the viaduct when sensors detect an earthquake.

The new system is designed to clear traffic from the aging and vulnerable structure of as quickly as possible within two minutes of the first signs of a moderate to severe earthquake.

“Recent events in Japan remind us how vulnerable we are and that earthquakes come without warning,” said Washington Transportation Secretary Paula Hammond. “These gates provide an added level of safety to motorists traveling on SR 99 while we work to take the viaduct down.”

On Saturday and Sunday, March 19 and 20, drivers should plan for a full closure of both decks of the viaduct from 6 a.m. to 6 p.m., between S. Spokane Street and the Battery Street Tunnel. The closure could cause increased congestion on I-5 and all major north-south routes. Real time traffic information is available at www.wsdot.wa.gov/traffic or by dialing 5-1-1.

During the closure, Washington State Department of Transportation (WSDOT) and city of Seattle crews will inspect the structure for settlement and perform routine maintenance and preservation work. WSDOT will release preliminary inspection results by March 25.

In addition to inspection and preservation work, WSDOT will conduct a series of tests of the new automated viaduct closure system. The system consists of nine traffic gates, similar to railroad crossing gates, controlled by a series of seismic-monitoring devices.

When sensors detect a magnitude-5 earthquake or stronger, the system will automatically close the viaduct within two minutes. Once the traffic gates are lowered, the entire viaduct must be inspected by WSDOT bridge inspectors before it can reopen to drivers.

During the tests, all of the gates, which are located at all viaduct access points, will lower simultaneously and warning lights will flash. Neighbors might hear alarm bells for short periods of time during the weekend maintenance closure.

The flashing beacons in West Seattle and on SR 99 announcing the viaduct is closed could activate intermittently during closure hours, because they are linked to the automated viaduct closure system tests. It is important to note that whether these flashing beacons are on or off, the viaduct will remain closed 6 a.m. to 6 p.m. on both Saturday and Sunday. The new system will be fully operational in April.

For more information about the automated viaduct closure system, visit www.wsdot.wa.gov/projects/sr99/viaductclosuresystem/.

For more information on the Alaskan Way Viaduct and Seawall Replacement Program, visit www.alaskanwayviaduct.org/.