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 Demon­stra­tion” made 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.)

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.