Interesting factoid – Did you also know that lots (most) government and WSDOT building projects come in on time and on budget? Check out their web site and read the quarterly reports: http://www.wsdot.wa.gov/projects – Republican propoganda notwithstanding, I’d bet WSDOT is better run than most companies.

It’s quite possible to do things as big as the viaduct replacement on budget, but not (as you said) with all the cost increases that come about because Seattle dithers forever trying to get consensus.

It’s a cut-and-cover tunnel, basically a submerged roadway with a lid. Much like the battery street tunnel, or the lids over I90 on Mercer Island, both of which has zero issues.

The big dig was hundreds of projects thrown together, miles longer and more varied than the viaduct, buried far deeper under the city.

Despite all the FUD, the tunnel and any elevated replacement are likely to be equally as safe (or unsafe), giving neither the edge in that regard.

Also – Any elevated replacement will have to dig far deeper and in different places than the current viaduct, with as much potential for unexpected ground-related issues.

To me the answer is obvious. Build the tunnel, but find a way to shift more of the cost differential to those that will directly benefit (property owners in that area and the city, which owns the piers + waterfront). People in Seattle are just so whiny about the “high” cost of infrastructure because they see numbers higher than what they saw 20 or 30 years ago. They can’t seem to get over the fact that the continued growth of Seattle (and King County) over the last 50 years necessitates major infrastructure improvements, and those have price tags in the billions. Unless we want to start shrinking as a city, get used to these numbers.