Crews finish future SR 99 off-ramp on time and on budget

Posted on May 31 2017 11:53 AM

The Alaskan Way Viaduct Replacement Program is more than just the tunnel – it is 32 projects that together will replace the viaduct with a new tunnel, highway connections, and a new Alaskan Way surface street. This month contractor Interwest Construction completed the South Dearborn Street off-ramp bridge, the 24th completed project of the viaduct replacement program.

Completed on time and on budget, this remarkable little bridge won’t have an immediate effect on anyone’s commute. The bridge currently stands isolated in the construction zone to the west of CenturyLink field. When the SR 99 tunnel is nearing completion, crews will connect this ramp to northbound SR 99, turning it into a northbound off-ramp to South Dearborn Street. After the tunnel opens, drivers heading to the stadiums or downtown Seattle will take this ramp.

What makes this bridge special is the earthquake technology it contains. As we’ve profiled in the past, this bridge is the first in the world to pilot-test a method for making bridges earthquake resistant. Its design uses memory-retaining metal rods and bendable concrete composite so the bridge flexes when the ground shakes, then snaps back into its original shape once the shaking ends. This video explains how this new technology works:



This off-ramp is one of several ways the AWV Replacement Program is improving Seattle’s resilience in the face of earthquakes. The viaduct is susceptible to earthquakes, and replacing it is, first and foremost, a safety project. Tunnels are one of the safest places to be in an earthquake because of the way they can move with the shifting ground, and the SR 99 tunnel is designed with earthquakes in mind. This post from 2016 explains how the SR 99 tunnel is built to withstand up to a 9.0 magnitude earthquake.

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