Sunday, July 30, 2006

Build the Elliott Bay Bridge

A persistent issue here in Seattle is the question of what to do with the Alaskan Way Viaduct. The double-decker roadway, which runs along the waterfront beside downtown, is in danger of collapse if we have a strong enough earthquake. This is a life-and-death issue, so of course the Seattle politicians have spent the past few years proposing and discussing and attacking and not actually getting anything done. I wonder if they -- and Mayor Greg Nickels in particular -- would be happiest if the "ugly" thing just fell down. Then they wouldn't actually have to make a decision.

The politicians have managed to limit the discussion to a choice between completely rebuilding the viaduct and replacing it with a tunnel beneath its current location. The tunnel (which would be below sea level) is estimated to cost $4 billion by its supporters -- so you know it would actually cost more than that. The replacement option would cost $2 billion, supposedly.

A vocal group has been pushing for just tearing the old structure down and replacing it with nothing. All traffic, they say, would be absorbed by the surface streets. While this would undoubtedly cost the least of any option, in terms of upfront costs, it would be disastrous to Seattle's economy. Residents and businesses would escape the unceasing gridlock by relocating to other cities. Perhaps the supporters of this idea are from Tacoma or Portland. . .

Last week, I heard a different idea: build a bridge over Elliott Bay. The proposed idea would be to build a cable-stayed bridge that branches off from highway 99 just where the viaduct starts by the mouth of the Duwamish River and then proceeds just off-shore up the waterfront to rejoin the current highway at the entrance to the Battery Street tunnel. Since cable-stayed bridges have a typical span of a quarter-mile, numerous piers would have to be constructed along the route.

When I first heard the bridge idea, I didn't know the proposed route and automatically assumed a different route entirely. I figured that when you say you're building a bridge over Elliott Bay, you're not just building it along the shore, a hundred yards off the end of the piers. I envisioned a route from West Seattle, on the west side of the Duwamish industrial area, across the open water to dive straight into the Battery Street tunnel:



The flags along the line represent pier locations a half-mile apart. This would match the longest cable-stayed bridge in the world, as well as the span of the Tacoma Narrows Bridge, a rather modest (nowadays) suspension bridge just down the Sound a few miles. The water of Elliott Bay is indeed quite deep, which makes pier construction difficult (and costly), but the techniques used in constructing the new Tacoma Narrows Bridge caissons would work even easier in Elliott Bay, for the lack of strong tides. Those caissons -- the bases of the piers -- now sit in 140' of water. The deepest caisson in Elliot Bay would be in 240' of water. But, as I said, no strong tides to mess up construction.

The shoreline bridge would have caissons at a depth of 150', since the bay floor drops off so rapidly from the waterfront.

The new Tacoma Narrows Bridge currently under construction is to cost $850 million. Double the cost for doubling the piers from two to four, add for the deeper caissons, subtract for reduced overhead, and the cost of an Elliott Bay bridge is realistically in the neighborhood of $2 billion.

Yes, it would still be half the cost of Mayor Nickels's tunnel scheme and the same cost as the replacement, and it would be a darn sight prettier, if you ask me. Especially if you get a world-renowned bridge designer to design the thing. Say, Santiago Calatrava, perhaps? Unless he's too busy with bridges in Spain and Dallas and Israel. Okay, let's hold a design competition.

Aligning the bridge from the west side of the Duwamish industrial area instead of the east has several advantages. First, it eases pressure off the perennially clogged West Seattle Bridge. Second, it gives ships room to maneuver once they pass underneath it. Third, instead of towering over the waterfront, the bridge would be at a quite photographable distance. And yes, people would photograph it. It would be a tourist attraction along the lines of the Golden Gate Bridge and the Sydney Harbor Bridge. It would bring even more tourists to the Jet City. The bridge would not be a view-blocking eyesore, as some may decry. It would enhance the view of everyone living and working upon the shores of Elliott Bay.

Fourthly, not nearly so many properties would need to be destroyed since this route would enter and exit the bay at nearly right angles, thus not wiping out long stretches of waterfront as the shoreline route would. In fact, if the bridge were done properly, the number of buildings knocked down could be counted on one hand. The people who are really in trouble are those directly between the Battery Street tunnel entrance and the waterfront. They'd be in the way no matter what happens elsewhere. West Marginal Way would need to be widened into a full highway from the bridge approach down to where Highway 99 crosses the river and intersects with Highway 509, and this would undoubted cause some displacement, also.

The benefits of a bridge to a tunnel or replacement viaduct (besides the cost) are several, as well. The bridge could be built while the existing roadway remains in use. There would not be years of gridlock during construction, as in the politicians' plans. Once the bridge is completed, the viaduct would be torn down and could be replaced with a wider version of the existing Alaskan Way or whatever else it is that Mayor Nickels would do with the waterfront once he had the highway buried underneath. Passengers on the bridge would have marvelous views of the city, the water, and the mountains -- something tunnel travelers would sorely miss. And as I said before, the bridge could solve the problem of the West Seattle Bridge at the same time.

So, an Elliott Bay Bridge is on the cheaper end of proposed alternatives; it solves the problem of construction congestion; it adds to Seattle's world-class harbor flavor; it reunites the waterfront with downtown; it serves the industrial areas and provides another connection to West Seattle; and yet it will never get built because the politicians in this city are stubborn, incompetent idiots. Bummer.

5 comments:

Geographicallychallenged said...

Interesting. It's a novel idea.

I read that one of the reasons Mayor Nickels wants the tunnel is because the sea wall needs to be rebuilt. With a tunnel, he can get state tax payers to pay for Seattle maintenance.

Pedicularis said...

Very interesting idea, with low risk (certainly compared to the tunnel/seawall project).

Have you considered how much it might cost to build a new four-lane freeway from the south end of your bridge down to the south of the First Avenue South Bridge, which is the north end of the Burien Freeway, to connect into the freeway system? Might add a few tenths of a billion.

Anonymous said...

This debate should continue, however, it seems the powers that be JUST favor two options. I am sure the Mayor and State Government just hopes this option goes away! The pros seem to give the Elliott Bay bridge more momentum; a pity it will never see the light of day!

Congratulations Mr. Mayor!

AAF said...

I believe we need to form a citizen's action committee to shove this proposal down down Gregoire's throat. I can't believe that this lone sensible solution hasn't been explored further. Lets develop the design proposal and make sure the citizens of the northwest know what the waterfront could look like. Lets also make sure we let it be known that the viaduct replacement is a much bigger deal than the monorail ever was and this bridge could drive this city into great worldwide status or let us follow along in a visionless role. If there's a citizen's group already organized, please post its meeting site, if not, can we propose a meeting?

Sotosoroto said...

I don't know of a citizens' group for this. If you want to propose one, go right ahead. I think I'd be too cynical to head the group, but I'd be willing to lend support.