During a presentation last week about the impacts tunnel construction will have on Pioneer Square, city and state transportation planners described proposed new tunnel as an "amazing" chance to redevelop the area into a dense, urban, transit-oriented community. Steve Pearce, viaduct program manager for the city's transportation department (SDOT), called tunnel construction "a major opportunity ... to really reshape a part of the city and create a more urban place, a more habitable place... while meeting our transportation objectives."

One element of the tunnel planners barely mentioned at last week's meeting, however, could prove a significant barrier to that goal: Two massive ventilation buildings, one at each end of the tunnel, equipped with huge fans that that would pull air out of the tunnel in case of an emergency. These buildings would be as tall as 65 feet in the south end and 85 feet in the north; would be largely vacant, especially during off-peak hours; and would include no street-level uses, creating a block-long dead space between Dearborn and King Streets to the south, and between Harrison and Thomas Streets to the north.

Yesterday, tunnel planners at the state transportation department (WSDOT) told me they're doing everything they can to minimize the negative impact of empty buildings on the street, including making the buildings (which are being designed by local architecture firm NBBJ) as transparent as possible, to allow people to watch the fans at work. "We want it to be open to the public, so that even if there's not a public use, it isn't walled off," Ron Paananen, WSDOT's viaduct replacement project manager, said.



The north portal ventilation building.

WSDOT planners also pointed out that removing the viaduct will open up acres of land for new mixed-use development to the south.

And they said the state is also looking at whether the south building  could include some street-level uses (which aren't currently part of the plan) such as storefronts and a public plaza. However, the north vent building—occupying a full block between Harrison and Thomas Streets, which will reconnect the streets north and south of Aurora Avenue—will have a maintenance shop at street level, with parking for industrial machinery and trucks, precluding any pedestrian-friendly uses.

And as critics of the project note, it's not like even a pretty six-to-eight-story ventilation building will be a plus for the neighborhood. "[The buildings will be] big and bulky, and there's going to be a huge amount of air flow, so they might be noisy," says Cary Moon, founder of the People's Waterfront Coalition. On the south end, she adds, the vent building will be "one more blow against that area being a walkable, pedestrian-oriented place."