(This post is part of a series.)

From the Seattle Times—no surprises, really, but worth noting:

The price tag for a new, elevated structure to replace the aging Alaskan Way viaduct has grown from $2.4 billion to $2.8 billion and the cost of building a tunnel has gone from a high of $3.6 billion to an estimated $4.6 billion, according to a report released today by the state.

Meanwhile, the estimated cost of building a new 520 floating bridge has grown from an earlier estimated high of $3.1 billion to $4.4 billion, according to the state Department of Transportation report.

Plain old inflation, coupled with unusually rapid rises in the cost of steel and cement (blame post-Katrina reconstruction, the rapid runup in energy prices, and rising demand in Asia), have pushed construction costs way up.

It’s not just for highways, of course; from what I’ve heard and read, construction costs have risen for homes and commercial construction projects.

And that means that we can probably expect the same sorts of cost increases plaguing things like light rail, too.  Which suggests this: no matter how you slice it, mobility just isn’t as cheap as it was just a decade or so ago.

UPDATE:  It looks like the figures above are the low end estimate for cost increases. The scaled-back “core” tunnel project could cost as much as $5.5 billion, and the “core” aerial highway as much as $3.3 billion. See the figure here, from the Seattle P-I, for more detail.

Unusually enough, the range of uncertainty in construction costs has escalated, rather than fallen, as time as passed.  I’d expect that cost uncertainty would narrow over time, as more of the planning is completed, and the project scope is better understood.  But in this case, commodity and construction prices have become so volatile that it’s really hard to tell what things will cost in a few years—which suggests that the public might never have an accurate cost accounting for the Viaduct or SR-520 until the projects are nearly complete.  Oi.