The city is pushing a one-time tax bill called a "local improvement district" to property owners in downtown for the benefit of better views and higher property values once the viaduct is gone. There is speculation of pulling a second LID for improvements in the area of Key Arena to coindide with the new NHL team http://mynorthwest.com/1242618/dori-rob-johnson-seattle-nhl/
The tunnel may be necessary but it's not all rosy as the WaPo article makes it out to be.