On September 20, the Washington State Department of Transportation (WSDOT) will release new cost estimates for two viaduct-replacement options, a cut-and-cover tunnel and a new aerial viaduct. (Unsurprisingly, WSDOT did not bother studying the surface/transit option.) The new estimates come in response to Governor Christine Gregoire's request for updated figures.

Two weeks ago, a state-appointed expert review panel found that WSDOT's cost-inflation assumptions were "overly optimistic," relying as they did on historic cost-inflation figures, not current construction cost increases. The difference between the old and new inflation rates is substantial: 2.4 percent, versus current annual construction inflation rates between 6 and 10 percent. In recent weeks, Sound Transit has run into similar problems with its cost-inflation estimates. According to the Daily Journal of Commerce, the light-rail agency assumed inflation during light-rail construction of 3 to 4 percent; actual costs for construction materials, meanwhile, have been rising between 10 and 15 percent every year.

It shouldn't come as much of a surprise, then, that Wednesday's cost estimates are expected to be higher than the current high estimates of $3.6 billion and $2.4 billion for the tunnel and aerial rebuild, respectively. "My sense," says council transportation committee chair Jan Drago, "is that they're going to be higher—probably much higher—for both projects." The new estimates could prove so alarming that the council decides against putting the options on the ballot—especially if the tunnel appears too expensive.

No one on the city council, with the exception of David Della, is actively supporting the aerial-rebuild proposal, so a public vote in favor of the rebuild would, in the council's view, be a disaster. (The most recent polls show the rebuild neck and neck with the tunnel.) The rebuild, Council Member Peter Steinbrueck says, "is our common foe." The state legislature, meanwhile, seems to be lining up behind the less-expensive rebuild, although nine Seattle legislators sent Gregoire a letter Monday supporting the tunnel.

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"We've spent hundreds of hours in meetings discussing this project, so why are we even discussing a vote?" Council Member Tom Rasmussen says. "I think this is why people elect us." A majority of the council now reportedly agrees with Rasmussen. As Drago puts it, "it's too complicated a project and we don't have the final numbers. If we didn't learn anything from the monorail, we're nuts!"

The state's expert review panel expressed a similar view, noting that "as some agencies have found out the hard way, approving and publicizing an overly optimistic estimate of project costs—or 'low-balling' the estimate to obtain initial project approval—becomes a significant liability as the project matures and the cost and schedule grows." Moreover, the panel pointed out, the city and state have not secured the funding they will need to build the $4-billion-plus tunnel. The panel called the city's projection of $40 million in federal funding "optimistic," and said it was "skeptical" that another $153 million in anticipated state funding "is viable, given that sales tax revenue"—the source for the presumed $153 million—"is typically earmarked for the state's general fund." On Wednesday, the city will find out whether the state concurs with that rather pessimistic view.

barnett@thestranger.com