When a committee of experienced financiers this fall examines the financial options available for rebuilding or replacing the Alaskan Way Viaduct in Seattle, it probalby will slow down a groan a bit when it gets the proposal offered today by Mayor Greg Nickles.

Not because it’s irrational or unfeasible. But there’s an uncomfortable amount of betting on the come involved in it, and for that reason we suspect the search for a winning formula probably will go on.

To back up: The Viaduct is a roadway roughly paralleling the shoreline of Elliot Bay in Puget Sound, between the water and the downtown hillside. the roadway is raised and limited-access. For some , it is a visual abomination; for us (and we fit mainly into this camp). It’s a great piece of transportation workmanship, because it actually allows drivers to swiftly (most of the time) cross from one side of downtown to the other. The problem is that it is unstable. A single serious geologic jolt could bring it crashing down.

Dealing with it somehow is going to be expensive, and there’s no way around that. Maybe the least expensive way would be eliminating it and throwing traffic onto the surface streets, but in this already traffic-clogged city, few have the stomach for that. The other options: Rebuild it more sturdily more or less where it is, or build a tunnel underneath. The former now has an estimated price tag of up to $2.4 billion, the latter about $3.6 billion. You can reasonably expect both numbers to rise with time.

Here’s the catch: As matters now sit, there’s maybe enough for the viaduct rebuild but definitely not enough for the tunnel. About $2 billion is available for either from the new gas tax money approved by the legislature and then by voters last year. Another $400 million or so has been earmarked. After that, you’ve got to scramble for bucks.

That might seem to give the rebuild a definite edge over the tunnel idea. But Nickles, a tunnel advocate, was determined to find the extra money. And he has located it, more or less – enough, he estimates, to bring the kitty to about $5 billion.

The problem is that some of it looks a little iffy.

Apart from the $2.4 billion already in the pot (most of that gas tax money), the rest is “Anticipated and potential revenue sources.” That should be a red flag. Here’s the list:

$280 million – Federal (transportation funding sources extending through two federal funding cycles)
$200 million- U.S. Army Corps of Engineers (Seawall)
$60 million – Federal Emergency Relief funds for the earthquake damage and risk to the current viaduct
$800 million – RTID
$150 million – Tolls
$177 million – Sales tax rebate on RTID-funded projects.
$400 to $500 million – Utility relocation
$250 million – Downtown area Local Improvement District for areas near the project
$20 million – City of Seattle transportation funds
$200 million – Port of Seattle

Much the largest single chunk is $800 million from a proposed Regional Transportation Investment District; transportation officials hope to place a plan for funding it on the 2007 ballot. Note the caveats: They hope to put it on the ballot (it may not get there) and they hope it will pass (it may not).

There’s $400 million for utility relocation (always a big piece of such projects). The mayor’s office says that ratepayers won’t be stuck with proposed rate increases (which could be contested and rejected); but if not, where does the city find the $400 million?

And so on it goes. And drawing substantial criticism already.

It’s a hopeful plan, but it could easily ride for a fall. Expect some changes when the finance experts get through with it in a few months.