NPI's Cascadia Advocate

Offering commentary and analysis from Washington, Oregon, and Idaho, The Cascadia Advocate is the Northwest Progressive Institute's unconventional perspective on world, national, and local politics.

Monday, January 7th, 2019

Safety First! New WSDOT video explains how SR 99 tunnel is designed to withstand quakes

In the autumn of 2005, with the Novem­ber gen­er­al elec­tion just days away, rep­re­sen­ta­tives of the North­west Pro­gres­sive Insti­tute stood on the 1st Avenue South ramp to the Alaskan Way Viaduct to make the case against John Carl­son and Kir­by Wilbur’s Ini­tia­tive 912, which would have wiped out fund­ing to replace the viaduct. Our “Viaduct Haz­ard Demon­stra­tionmade the night­ly news, and KIRO7 even pro­vid­ed aer­i­al footage to go along with their sto­ry.

Over eleven years lat­er, we are final­ly about to tear down what is left of the Alaskan Way Viaduct, with its replace­ment tun­nel due to open in just a few weeks. (The south­ern por­tion of the struc­ture was demol­ished in 2011.)

Still image of the new SR 99 Tunnel provided by WSDOT

The new State Route 99 tun­nel, under con­struc­tion (Cour­tesy of WSDOT)

WSDOT has appro­pri­ate­ly released a new video that explains how the new deep bore tun­nel is designed to with­stand earth­quakes and why the tun­nel is actu­al­ly a place you’d want to be if The Big One shook Seat­tle.

It may sound coun­ter­in­tu­itive, but a tun­nel like the one that will soon car­ry SR 99 under­neath down­town is actu­al­ly the best place to be in an earth­quake.

And that’s because tun­nels move with the earth.

WSDOT has been try­ing to explain this con­cept to the pub­lic and the media for years, but unfor­tu­nate­ly it has­n’t become as com­mon­ly under­stood as it should be. I’m lucky: I got a first­hand expla­na­tion decades ago, dur­ing my time in Scout­ing.

That expla­na­tion came dur­ing a guid­ed tour of the I‑90 Mount Bak­er Tun­nels, when I got to see the oper­a­tions cen­ter and the work WSDOT does behind the scenes to keep the facil­i­ty run­ning. What I most remem­ber about that tour is the engi­neer explain how tun­nels are earth­quake-resis­tant struc­tures. Were there to be a quake, he said, the Mount Bak­er Tun­nels are where he’d want to be.

I mar­veled at this knowl­edge and nev­er for­got it.

WSDOT wants all Wash­ing­to­ni­ans to have a bet­ter under­stand­ing of why cer­tain facil­i­ties (like the new SR 99 tun­nel, one of many tun­nels in Seat­tle) per­form bet­ter in quakes than oth­ers (like old bridges).

So they made this video, which opens with footage of the 1989 Loma Pri­eta earth­quake in Cal­i­for­nia, which caused the col­lapse of the Cypress Street Viaduct.

It’s real­ly well done, and I hope you’ll take a few min­utes to watch it today.

This Fri­day will be the last day that the Alaskan Way Viaduct is open to traf­fic. After that, the viaduct will be tak­en out of ser­vice. The tun­nel will open a few weeks lat­er, bar­ring any prob­lems or delays with recon­fig­ur­ing the new ramps.

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One Comment

  1. Aren’t para­dox­es grand?

    # by Leno Lorentz :: January 13th, 2019 at 11:53 AM