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Washington State and Seattle DOTs install new earthquake closure system on viaduct

In a co-project, Washington State Department of Transportation (WSDOT) and the Seattle Department of Transportation (SDOT) have installed and are testing a new system of sensors and automated emergency gates, which will close the vulnerable SR 99 Alaskan Way Viaduct in Seattle to traffic in the event of an earthquake. The US$5.5 million system is calibrated to be triggered by an earthquake of magnitude 5 or greater, which is the threshold at which engineers expect there would be damage to the viaduct without the threat of sections collapsing. The new system is designed to clear traffic from the aging structure as quickly as possible, within two minutes of the first signs of a moderate to severe earthquake. The current process to close the viaduct to traffic can take up to two hours and requires the help of many emergency response teams.

The new system consists of nine traffic gates, similar to railroad crossing gates, located at all viaduct access points and controlled by an earthquake detection system. When the earthquake detection system detects a magnitude-5 earthquake or stronger, all of the gates will lower simultaneously, warning lights will flash, bells will ring and the system will automatically transmit a message alerting WSDOT’s 24-hour traffic management center and SDOT that the viaduct is closed. The system consists of seven sensors, which resemble bulky smoke detectors, placed evenly along the central waterfront stretch of the double-decker highway. At least three sensors will have to register a 5.0 quake before the system is activated. WSDOT says road construction and large trucks are unlikely to register false readings.

Matt Preedy, WSDOT’s project director, said, “Without the gates, it could take us up to two hours to clear the corridor. This way, our personnel don’t have to place trucks in front of the ramps. It’s a much better distribution of our emergency forces.” Preedy also said the viaduct could not withstand another jolt on par with the 2001 Nisqually Quake, which at 6.8, damaged support columns and joints. “If that had lasted 10 seconds longer; it’s likely the viaduct would not be here,” he said. The federal grant for the project also provides funding to extend WSDOT’s existing fiber-optic communications network from I-90 to the intersection of First Avenue South and South Atlantic Street near SR 99. The new fiber communications extension will be part of the system used to notify WSDOT’s traffic management center, other agencies and emergency responders, if the automated viaduct closure system is activated. The extension could also be used to connect into future fiber communication networks along the SR 99.
 

March 23, 2011

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