If we had to choose between a new viaduct or a deep-bore tunnel, which should we choose? First, I think the reality is that a deep-bore tunnel will be constructed since “important” people are interested in it succeeding. If I’m wrong and the tunnel project does collapse, the ensuing political chaos would result in an environment where surface/transit/I-5 has just as much of a possibility as being built as a viaduct.

However, for this first part, let’s assume we could choose just between a new viaduct and the tunnel. Martin has gone to great lengths to show that the city would save hundreds of millions of dollars if a viaduct were built instead of the deep-bore tunnel. It’s true, but money saved isn’t necessarily spent and it’s not obvious that Seattle would tax itself to invest in transit and bike projects just because it would have taxed itself for a deep-bore tunnel. Major transit investments like the Central Streetcar are dead-on-arrival — there isn’t local political support — and we wouldn’t see money from the state for transit: improvements beyond basic mitigation are certainly considered optional by the state. The state has already ignored the transit funding it agreed to with the deep-bore tunnel agreement.

Photo by Oran.

These things are important, because in any scenario where a viaduct is being rebuilt is over the very strong objections of the Seattle mayor and city council members: if the state is already overruling us, why would they sweeten the pot? Heck, why not build a bigger viaduct or one with more off-ramps? And if the city is upset with the state, would it partner on strategic transit improvements?

After all, the transit elements of the rebuild plan were included in the same stakeholder process that was completely ignored when state and local officials agreed to build a deep-bore tunnel. I think Martin’s comparing a fully politiked deep-bore tunnel to a conceptual viaduct. It could be the case that a rebuild would result in tremendous local spending on transit, but even more transit spending is possible with surface/transit/I-5 where transit is moved near the forefront of the plan.

More after the jump…

That is, we shouldn’t assume a rebuild and a tunnel are the only two options. The rebuild option is just as dead as surface/transit/I-5 and to resuscitate one necessarily resuscitates the other.

Much of the intrigue regarding the tunnel has to do with Seattle’s mayor his relationship with the city council, a group that is much more amenable to surface/transit/I-5 than a rebuild. I don’t think it’s just the state legislature that matters; clearly a rebuilt viaduct is a favorite of business interests that would lobby the legislature, but if the deep-bore tunnel project collapses I’m not sure that’ll be an excuse to ignore what the city desires about the basic premises of the highway’s design. The “pragmatic” and the business community who would support a viaduct currently form the coalition supporting the deep bore tunnel, and they’d lose credibility if the tunnel collapses.

Surface/transit/I-5 is the best alternative, but my intuition is that a bypass tunnel is better for our urban environment than a rebuilt viaduct that serves downtown. If all our highways bypassed our urban core, we’d have a much better transit network for it. Admittedly, a rebuilt viaduct with just Western ramps would be a substantial improvement over today’s viaduct, but I’d ask Martin to reconsider whether those ramps are a “bonus.”

The waterfront will not be a dense, urban neighborhood as some of us hope, but in any case it can still be much better than merely the shadow of a highway. There may be some reason for optimism regarding the waterfront. While the best option is that the city opens up its requirements to allow for more waterfront development in conjunction with the park, a showpiece urban landscape that combines some local business with an interesting park may turn out to be a better thing for the city than we expect. I think a waterfront park can be simultaneously all three: 1) a wasted opportunity, 2) better than a viaduct, and 3) something we’re proud to have.

Finally, who wants to say we had the chance to tear down an elevated roadway on our waterfront but decided to rebuild it instead? What compels me to write this post is the fact that I do not want a viaduct along my waterfront and I suppose I’d swallow a tunnel if I had to. It’s almost entirely emotional, I admit.

45 Replies to “RE: Viaduct or Tunnel”

  1. It comes down to whether Seattle wants to

    1)Maintain the existing barrier twixt city and docks, which I suppose will make a nice park like the High Line in Manhattan, when it becomes redundant after Peak Oil really kicks in.

    2)Build a tunnel that may make the Boston Big Dig project look on-time and corruption-free.


    3)Repeat the economic success of the Embarcadero-transformation which was completed in little time with relatively little cost and no international-scrutiny (because it was not that big a project).

    Consider also Seattle, if you dare, what a bold statement it would be to the Traffic Engineering and Asphalt-building cabal and the rest of the world, that an American city decided to remove an express-way and not replace it.

    Throw in a couple of windmills to power the renovated Waterfront street-car and you might even see a new level of tourism.

    Of course, you could just wait for Mother Nature to do the job for you!

      1. Seattle wouldn’t be the first city to say “No” to the concrete cabal. Portland did so about 20 years ago. And while our total transit numbers (percentage) are better than theirs, our bicycle traffic is 1/2 theirs.

  2. Erik, whether you want a tunnel or not, comparisons to the Big Dig are misleading and wrong. The Big Dig was a huge project involving multiple bridges and tunnels. This is a relatively simple bore done around the world. The main risk is the breakdown of a boring machine. Not inconsequential, but a relatively known risk.

    Your comparison with the Embarcadero is also somewhat wanting. That freeway was a loading zone for the Bay Bridge, not a throughfare.

    That being said, I am okay with no tunnel if that is the way it is to go, but I will never favor building another viaduct on our waterfront.

    1. The main component of the Big Dig was to place the Central Artery into a tunnel. You can remove the Ted Williams Tunnel (extension of I-90 to Boston’s Airport) and the Bill Buckner/Lenny Zakim bridge from the totals and you will still have a project that was enormously delayed and over-budget.

      With the Deep Bore Tunnel proposed for SR99, there will still have to be substantial work to move utilities and ensure that structures above are not compromised. It will be “easier” than the Central Artery Tunnel, but it will still be a risky task.

      The Embarcadero Freeeway was supposed to be the route of US10 from the end of the Bayshore Freeway to the Golden Gate bridge. It was never fully completed and so was easier to remove. But then was the SR 99 viaduct ever fully “completed” given what happens to the “roadway-experience” around where it passes the Systembolaget (State Liquor Store) warehouse.

      SR 99 on Aurora operates fine with traffic signals and at-grade crossings.

      SR99 on East Marginal Way operates fine with traffic signals and at-grade crossings (it even has a drawbridge that frequently opens!)

      So why won’t SR99 *on* Alaskan Way not work?

      1. So why won’t SR99 *on* Alaskan Way not work?

        Because traffic patterns near/around downtown are not remotely the same as those in outlying areas of the city.

      2. What traffic patterns are those? Downtown to the West Seattle bridge? Downtown to N 46th Street? Are those enough to justify not making the viaduct a boulevard?

      3. I’m not saying that the traffic patters are or are not enough to justify not making the viaduct a boulevard. I’m saying that Aurora Ave N. North of Greenlake is not a valid comparison to SR99 around and through downtown.

    2. I think the Big Dig comparison is more similar than you think. We are considering a 50′ tunnel over a rail tunnel, next to a light rail tunnel, under dozens of skyscrapers, and through unstable and inconsistent soil. As an engineer, I see this project as incredibly risky and wouldn’t touch it unless I knew that I wouldn’t be responsible when a skyscraper’s foundation is swallowed by a sinkhole or the TBM gets stuck and has to be excavated, and then I would bill an arm and a leg for it. The Big Dig was incredibly complicated but most of the problems could be addressed during design. We won’t know what we are going to get until the TBM starts work.

      Let’s build the surface portion with an Alaskan/Western couple now, so that it can open when the viaduct is demolished, but reserve the option of building a bypass tunnel in the future. Then, in the meanwhile, the engineers can figure out a way to build this with less risk, or we will realize that we really don’t need the tunnel after all. I’d call it the “deferred tunnel” option.

      1. Nothing will ever be without any risk, but the risk you state for the DBT as currently planned is not nearly as bad as you seem to think.

        The DBT won’t go under the LR tunnel, and tunneling under an existing railroad tunnel is just not that big of a deal. After all, Metro did it twice in the 80’s when they built the DSTT and the clearances there were much tighter.

        On top of that, the actual cost to build the DBT bore is something on the order of only $300M. The rest of the DBT cost is in outfitting, roadways, systems, etc. And those are pretty much off-the-shelf commodities.

        We need to stop being afraid of our shadows at every turn and just get on with the task of making this a better city. Delay does nothing to improve this city.

      2. You’re right, we shouldn’t delay. Let’s build the surface portion now. If we wait for the engineering to be done on the tunnel, we will be years behind schedule. What makes this risky is the size of the buildings above the bore and the difficult soil. Boring can potentially destabilize the buildings above. The larger the building, the more bearing presure, the more risky tunneling underneath becomes. Building a cut and cover tunnel (which I would prefer) next to a tower is not the same as tunneling underneath. I try to keep up on projects like this. The local comparisson is the Brightwater bored tunnels, which had two TBMs stuck last year. Or there is the Beacon Hill tunnel which opened a sinkhole or two. I don’t know of any bored tunnel going under such large buildings in such poor soil. As much as I like the idea of the DBT, it, in my professional opinion (I am a civil engineer), highly risky. Not impossible, but I suspect the cost and schedule will be far higher than what is estimated at this time. This needs to be considered, especially considering the state of WADOT’s budget. There are far more important projects that can be built on time and on schedule.

    3. It’s not a “simple bore” it’s the largest single bore ever. And it’s being done in soft glacial till, not hard rock. The risk that one of the boring machines gets stuck, or that the soil sinks as it digs under the buildings is high.

      1. It’s the largest single bore by something like only 2 feet or so. That’s about a 5% change.

        A 5% change is not enough to scare any engineer worth his/her salt, and there isn’t any design “cliff” that makes a 5% increase in diameter impossible.

        Attempts to scare the uninformed public with such rhetoric are little more than rhetorical FUD.

  3. “What compels me to write this post is the fact that I do not want a viaduct along my waterfront and I suppose I’d swallow a tunnel if I had to”

    This is essentially where I’ve ended up on this issue, only I’d add that the 6-lane 30mph waterfront highway proposed by the surface option is worse for the waterfront than a viaduct rebuild.

    The controversy surrounding this issue shouldn’t be surprising, as all three options are a mixed bag. The biggest problem with tunnel is that it delivers low mobility bang for the buck, but when I think of the tunnel as an investment in the waterfront, I can hold my nose and get behind it.

    1. Absolutely. It mystifies me that folks who have been complaining for years that the Viaduct cuts off the waterfront from downtown would think that adding more (and busier) lanes of traffic would improve that situation. As a pedestrian, I’d take the current status anytime in comparison to that. (But unlike you, I can’t get behind the ridiculous DBT, even if I hold my nose. No transit in the tunnel? Then no support from me.)

  4. The one thing I haven’t been able to wrap my head around with the surface/I-5/transit option is how a large increase in through traffic is supposed to mix well with a high concentration of pedestrians (and pedestrian crossing) and ferry traffic. Am I missing something?

    1. Mike the influx of cars will be at low speeds. Frankly I would expect if this corridor is limited to 25mph traffic will go elsewhere.

      Frankly I’m shocked to see this state spend so much on car infrastructure projects, it really feels like 1965 around here some times. With peak oil the only thing that will matter is what is best for transit, not how do we let people in SOV’s bypass downtown…

      1. So that sounds like the answer is that both SOVs and bus lines (there are several that use the Viaduct) will have longer transit times. That would be fine if the transit portion included light rail from West Seattle to Ballard, but I don’t believe it does. Seems kind of lose-lose to me.

      2. Maybe West Seattle has been lucky to have a personal freeway for years, but those days are over.

      3. That’s really not cool, Mike Orr. West Seattle is part of the city and deserves decent mobility, as do other neighborhoods. And making their transit slower and more unreliable is not going to improve anything for anyone.

        I wonder of some of the anti-monorail campaigners in West Seattle are rethinking their positions yet…

      4. I agree that West Seattle needs good mobility, but I don’t think it’s entitled to forever have an expressway to downtown simply because 99 happened to be adjacent to it for several years. Ballard doesn’t have a direct freeway to downtown, nor does Rainier Beach, Maple Leaf, Madrona, etc.

  5. I mostly agree with this, but have to take issue with this:

    If all our highways bypassed our urban core, we’d have a much better transit network for it.

    How so?

    Making this worse for cars is not at all the same thing as improving things for transit. A large number of our most popular bus routes would be slower and less popular if they were not able to use the freeways to get to downtown. And they would cost more to run, as you would need more buses running to get the same frequency. And it would not create the money needed for the better transit we want.

    What’s more, this would direct a lot of development elsewhere. The reason jobs locate themselves downtown is because a lot of people can get there. If I-5 bypassed downtown more businesses would locate elsewhere and the regional development pattern would become more dispersed and harder to serve by transit.

    1. Eric, your comment seems to assume that people would live in the same places and in the same way if we didn’t have highways serving downtown directly. Our buses have use highways and people commute on highways because people live further from the urban core. In this alternate history, we’d certainly have a larger investment in rail and more density. I’m envisioning something like Vancouver, BC.

      PS, I should have said major highways — specifically I-5 and SR-99.

    2. Vancouver BC, London, Moscow, and pretty much all other European cities. These cities do have six-lane boulevards to the city center but not freeways. The freeways end at the edge of the city or in a ring road around the city. The US ended up with the Robert Moses model, with freeways going through downtowns. When Eisenhower approved the Interstate plan he got assurances from the DOT that it would not go through cities, but they were lying.

      In cities without freeways, rapid transit becomes the main way of getting around. This in turn cases the city to densify around transit stations, which is what makes the city more walkable and liveable.

    3. This is one of the problems with the DBT – because it won’t have any exits from the tunnel, it will bypass downtown and deposit cars at the ends of the tunnel en masse.

      1. Sort of. It doesn’t reduce the accessibility of downtown by much as compared to the status quo — it’s a couple more blocks from the exit, depending on where exactly your going. It does considerably reduce the accessibility of Belltown, Interbay, Magnolia, and Ballard relative to the status quo, but not relative to the surface option.

    4. Okay, none of these example cities built highways straight through their city centers with no exits, so it’s hard to be sure these are apples-to-apples comparisons. Vancouver never connected the highway on the south to the highway on the north, you just have to take surface streets to get through Vancouver. London and Moscow had extensive transit infrastructure before they had highways.

      If you simply mean that a long time ago we did not build I-5 and did build other infrastructure to help people get in to the city (but not through it), then I agree. If you’re talking about what would happen if we took a metropolitan area where most people rely mostly on cars to get around and removed all freeway exits to the downtown area but helped through traffic move easily, well, what would happen is the jobs and retail would relocate to more accessible (but less transit friendly) places. And the latter question is more relevant; we’re trying to get from point A (2010) to point B (a transit friendly 2030), not from point C (1940, maybe?) to point B, and so we need to find the best step from point A.

      1. Well, a fair amount of car-oriented retail would move to the ‘burbs but pedestrian- and transit-oriented retail could still thrive Downtown.

  6. 1. With so little access to Downtown Seattle can any Waterfront tunnel proponent tell me exactly what purpose this project is supposed to serve? Freight? Cars? Is there really that much through traffic on 99 now?

    2. Does anybody think that any other city in the world would take a “view” waterfront like ours and rebuild, let alone build in the first place, an elevated highway across it?

    3. Why is the Seattle Transit Blog, probably the best forum ever on public transit, spending so much time arguing road design, and so little transit possibilities? It seems to me that planning for the city neighborhood- including park space- that many of us would like to see, starts with electric rail, streetcar and “light-“.

    4. Has anyone presented any kind of a plan for any kind of transit as part of the Waterfront project? If all we’ve got is the phrase “I-5/Surface/Transit”, now wonder Olympia gives transit so little respect.

    Mark Dublin

    1. Is there really that much through traffic on 99 now?

      Being an almost daily observer of traffic on 99 I would have to say yes, there is a good deal of through traffic on 99 now.

      1. Yes, but how much of the traffic you observe is going from one end of the viaduct to the other and how much is getting on/off and the various exits along the route?

      2. There are two exits from the Viaduct going northbound and one going southbound. The one going southbound is low use. The two going northbound have heavy use in the morning and light use in the evening (when 99 is more congested). Even with the heavy use in the morning, there is still a fair amount of traffic that travels through the Battery St. Tunnel. I do not know what portion of that traffic is in order to avoid the Western St. exit, but I assume there is at least some.

        There is effectively one onramp for the Viaduct traveling northbound, and two onramps for the Viaduct traveling southbound. The one for northbound sees light traffic in the morning and moderate traffic in the evening. I can’t speak to the two southbound onramps in the morning, but they see heavy use in the evening.

    2. “Why is the Seattle Transit Blog, probably the best forum ever on public transit, spending so much time arguing road design, and so little transit possibilities?”

      Well, transportation is interconnected. But more importantly, major transit funding isn’t really on the table at this exact moment while the deep bore tunnel is funded.

    3. 1) An honest proponent would say, “The deep-bore tunnel is an express bypass from north Seattle to the airport and other south end destinations. We say it speeds up port freight in order to get public support for the project, but actually it will slow down port freight because the exits are in the wrong place for them so they’ll have to use the local street, and long-distance N-S freight is not likely to leave I-5. The bypass does not serve downtown, but downtown already has more road and transit alternatives than anywhere else so they can shut up.”

      2 & 3) Effective decisions are a compromise among the public, businesses, and governments as a whole. In a democracy we can’t impose our will on the entire community, or impose unlimited taxes to build the perfect city. Expecting the highway lobby and its sympathizers to go away is not realistic. The decision on the viaduct was made in the 1930s when it was first built. A rebuild is not a new highway, it’s essentially maintenance work. I-5 has a severe bottleneck downtown with only one through lane each direction, and no room to expand. 99 is a relief valve when I-5 gets too backed up. So what other city has decommissioned a waterfront freeway that plays such a major role in the region’s highway system?

      We should built the smallest and cheapest automobile capacity we can. But we have to be realistic that we aren’t the only, or even the main, decision-makers, so there will have to be some kind of viaduct replacement.

    4. http://www.seattle.gov/transportation/docs/seawall/Oct10/ConceptPlanDNorth.pdf

      These draft SDOT Concept ‘D’ drawings are from the oct 19th presentation from this city website:


      From this page, other Concept drawings are good to copy and print. Concept ‘D’ shows the proposed plaza widths, blank Alaskan Way, sidewalks and curb extensions on both sides, seawall edge proposals. Best I’ve found.

  7. Thanks, Mike. But think about this, John: this time of year a lot of dogs and cats aren’t supposed to be “on the table” either, but a lot of ham and turkey ends up on the rug or under the couch through concentrated interest and sheer four-footed gall.

    Besides, the only way things get on the table in the first place is if somebody puts them there. The late monorail idea may have been a turkey, but it did spend awhile on the table. Something on a better plate of engineering might get to be in the meal.

    You never know when a good idea might be the one whose time has come.

    Mark Dublin

  8. As I said in the last article, it will create a new Waterfront neighborhood. The entire area between First Ave and Alaskan Way, now mostly dead, will become vibrant, with existing historic buildings revitalized and the many (underused) parking lots and vacant lots built upon. I’m excited. Oh, and I can see a bunch of cool retail going in on the ground floor of the buildings that currently face the Viaduct.

  9. I’m sure tired of seeing stories about the Viaduct. Can’t we just move on instead of constantly revisiting a decision over and over again?
    Now, I haven’t seen Martin’s analysis, but hopefully it factored in what we didn’t see in the media: (a) tearing down the Viaduct to rebuild it would involve 3 – 4 years of having no Viaduct, but the costs of doing so were never added to the cost of that option. By comparison, the deep bore tunnel is estimated to have a few to several months of “no Viaduct.” (b) Any replacement Viaduct would need to be replaced every 50 years, or twice every 100 years. The deep bore tunnel has a 100 year life cycle. Therefore, to make the costs “apples to apples,” the cost of the replacement Viaduct should be doubled.

  10. I’m surprised to learn the Seattle Transit Blog considers the Central Line Streetcar politically dead.

    It may not be a part of the state’s plan, but it is the top priority among the citywide network plan adopted by City Council in 2008 and represents the crucial connector that could breathe life into the Seattle Center, the Central District and Pioneer Square…

  11. http://www.seattle.gov/transportation/docs/seawall/Oct10/ConceptPlanDNorth.pdf

    These draft SDOT Concept ‘D’ drawings are from the oct 19th presentation from this city website:


    From this page, other Concept drawings are good to copy and print. Concept ‘D’ shows the proposed plaza widths, blank Alaskan Way, sidewalks and curb extensions on both sides, seawall edge proposals. Best I’ve found.

  12. I’ll bet the new waterfront park won’t be named after any state political figure. Or any non-Irish surnamed municipal politician. Assuming the rights-of-way air rights aren’t auctioned off to help pay for the world-class price tag. Sheesh.

    Lazarus, regarding extrapolating beyond the engineering world’s state-of-the-art limits, it is in human nature to want to use things beyond their intended range. I would recommend reading “Success through Failure: The Paradox of Design” and “To Engineer Is Human: The Role of Failure in Successful Design” by Henry Petronius, an accomplished author and civil engineer.

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