• Via Seattle Municipal Archives on Flickr
Cary Moon is director of the People's Waterfront Coalition, a group advocating for waterfront and transportation solutions. — Eds

Much of the support for the bored tunnel under downtown Seattle relies on the assumption that it would make the cars disappear on one end of downtown and reappear on the other. But the tunnel must emerge from the ground somewhere, and recently released plans show it ain’t pretty.

As designed by the Washington State Department of Transportation (WSDOT), the tunnel’s southern portal would be next to Pioneer Square. The portal design includes a highway interchange, just south of King Street on Alaskan Way, providing the ramps for all SR-99 travelers trying to get to and from downtown (.pdf). Next to the stadiums, WSDOT wants to build two on-ramps, two off-ramps, and a block long freight flyover—in addition to the highway itself.

According to WSDOT’s predictions, about 59,000 cars a day will be channeled onto the few streets in this area, mostly on First Ave or Alaskan Way. First Ave currently carries about 25,000 cars a day, and Alaskan Way about 12,000. To get a picture of an additional 60,000 cars on these streets, imagine the same traffic volume as Lake City Way.

There's more. WSDOT’s new tolling study released this month (.pdf) shows the state expects about 30,000 additional cars to divert to city streets each day to avoid the toll. Worst case, we could see 90,000 more cars trying to get through Pioneer Square each day.

Pioneer Square community leaders are alarmed, knowing that their most valuable asset is threatened: the unique urban ecology of narrow streets, a walkable neighborhood, and small businesses in one of the finest historic commercial districts in America.

The folks at the Seattle Department of Transportation deserve props for developing a solid list of principles for protecting urban character and hiring capable consultants. But highways attract traffic. Exploiting the streets of our struggling historic district streets as on-ramps is just wrong.

To contemplate these potential impacts, the American Institute of Architects, Great City, and the Pioneer Square Community Association hosted a forum on Friday (full disclosure: I was one of four panelists). Two things became clear. First, improving transit service, as promised by Governor Christine Gregoire last January (but still not funded), is crucial for Seattle. WSDOT's own traffic models show that If transit is built, and service is frequent, a huge number of these drivers would choose it instead. Second, the City of Seattle must oversee WSDOT's project. Among other measures of accountability, an expert review panel with legal, technical, and design expertise should protect Seattle's interests. Otherwise, we could end up paying a billion dollars per mile for a highway that does a poor job of providing access to downtown, offers NO new transit, and turns historic-district streets into highway access ramps.