The state released its Final Environmental Impact Statement on the deep-bore tunnel last week. I've been wading through the thousands of pages—the report’s body is thicker than a Bible and sits on top of appendices A through X, including some appendices that come with over 250 exhibits—and so has Clark Williams-Derry over at the Sightline Institute. I'm working on a longer a piece about it. Meanwhile, Williams-Derry plugged a few of the traffic estimates into a nifty bar graph to compare traffic volumes downtown if we build the tunnel or if we shut down the viaduct and do nothing at all:

  • Sightline Institute

Sightline keyed in on the same problem we predicted the report would reveal. Because so many cars would exit Highway 99 to avoid the tolls, most of the downtown grid, the central waterfront, and I-5 is no different with a tunnel or if we just shut down the Alaskan Way Viaduct.

But there are a few marginal benefits, says Williams-Derry:

As you can see, compared with an earthquake that closes the Viaduct, the state says that the tolled bored tunnel would modestly reduce traffic volumes in lower Queen Anne, on streets in the downtown core, and reduce them a bit more in Alaskan Way through Sodo.

But the bored tunnel would make traffic a little worse in South Lake Union. And it’s basically the same as an earthquake for the waterfront, First Hill and Capitol Hill, and traffic crossing between Sodo and the ID/Pioneer Square... I-5 tells a similar story: the state’s models show that tolls on a new SR-99 facility will divert significant amounts of traffic onto I-5.

The tunnel's great advantage is that it facilitates an additional 40,000 vehicles a day under downtown (or 57,000 vehicles by 2030, if WSDOT's prediction of increasing traffic holds true, despite reports that traffic is actually declining). Bypassing downtown in the tunnel would save drivers—that is, those who can pay the $5 tolls one direction—from the snarl of traffic up above. However, as Williams-Derry writes, "in terms of center city traffic delays, the tolled bored tunnel is actually one of worst performers among the options studied."

Here's why this information should inform the debate around the project: The tunnel backers insists that failing to build the tunnel will result in a "stalled city," "gridlock," and a "parking lot on I-5." The problem with that argument: For most of downtown is that a tunnel also creates "stalled city," "gridlock," and a "parking lot on I-5."