From eight-digit repair to ten-digit tunnel: Here’s the West Seattle Bridge Cost-Benefit Analysis

By Tracy Record
West Seattle Blog editor

Just released by SDOT, here’s the Cost-Benefit Analysis (CBA) meant to help inform the city’s decision of what to do about the seven-months-closed West Seattle Bridge:

(It’s also on the city website. Added 10/26: Here’s a link to the 628 pages of appendices.)

Though it looks at six options for repairing or replacing the bridge, the renderings and costs are NOT by any means the final set of options – they’re what was roughed out for comparison purposes. It should also be noted that the CBA does NOT address the newly emerged option that some have nicknamed “rapid replacement” – though that will be explained at tomorrow’s West Seattle Bridge Community Task Force meeting, along with the CBA. But if you just want to skip ahead to the bottom line, those estimates are on page 68 of the 89-page document, with basic up-front construction cost rough estimates from $47 million for repairs to $1.9 billion for an immersed-tube tunnel.

Here’s the CBA document’s purpose as explained in its Executive Summary:

This CBA addresses some of the questions we have all grappled with since March 23 – What long-term impacts will this closure have? Can the City afford to wait for a replacement? What is the life span of a rehabilitated structure? What benefits does rehabilitation offer? What benefits does replacement offer? While the purpose of this report is to objectively present the benefits and drawbacks of multiple alternatives, to help inform the decision to rehabilitate or replace the bridge, its findings will not, and should not, dictate that decision.

The CBA is, in fact, just one factor in this decision, focused on helping to support decisions being made around public safety and technical risk. The decision will also be informed by external exigencies and current events, by the recommendation of the asset owner, SDOT, as well as by the guidance provided by the Technical Advisory Panel (TAP) and Community Task Force (CTF). Ultimately, the imminent decision to rehabilitate or replace the structure will be a City decision based on a value judgment for the safety and well-being of the people of Seattle.

Now, the toplines of the document, prepared by WSP, a consulting firm that SDOT has long been working with:

First, the document explains how the previously discussed finding was reached, that nothing suggested the bridge wasn’t fixable. It also notes:

As information is received in real time through the biweekly in-person inspections and 24-hour monitoring system, we learn more about the bridge and how it is behaving, allowing us to make more informed decisions. What we have learned to date has yielded confidence that the bridge behavior is predictable and that it is technically feasible to rehabilitate the bridge and restore its remaining service life, or more. However, we will continue to perform reconnaissance work to see if trends change as we finalize stabilization measures this fall.

Here’s how the studied possibilities were decided on:

The CBA began with five alternatives, all of which were on-alignment and fit the same grade/profile as the current bridge. In response to community feedback, the study adopted a sixth alternative – an immersed tube tunnel (ITT). This is the only alternative that deviates from the current alignment and grade/profile. During this process, we also eliminated the third alternative, a partial superstructure replacement, from consideration as it was determined that it was not the apparent low-cost option for a rehabilitation alternative. Section 2 of this report includes full alternative descriptions and details of each concept. WSP chose five representative alternatives based on apparent low cost to fit within the scope and schedule confines of the CBA. There exist other options within each category, many conceptually mentioned within the appendice that could and should be further explored or developed.

Since one giant question is “how much would (any option) cost?” it should be noted that the CBA says, “For each alternative, WSP developed ROM estimates for initial capital cost (inclusive of monetized risk items) and for life cycle costs. Life cycle costs include allowances for initial capital investments, operation and maintenance costs, inspection costs, and future repair/rehabilitation costs.”

The document goes into details of each type of option evaluated – including repair, which gets the formal title “direct strengthening to restore live load.” Here are the options, as screencapped from the CBA and as previously reported, with estimated durations:

Repairs are projected to last 40 years and to be able to reopen the bridge to traffic in 2022, with some additional seismic work required in the 10 years after that, and the bridge needing replacement by 2062.

Another duration-related note – how much closure time is estimated for each option. From the CBA:

The continued closure causes increased vehicular traffic using detour routes through marginalized communities. Because the overall closure duration was similar for Alternatives 2, 4, and 5 (even if in two phases), these were rated as better than Alternative 1, which would require two closures totaling 7.5 years, or Alternative 6, which would require one closure totaling 9 years.

For this measurable, rehabilitate and replace (except Alternative 6) have similar outcomes – the only difference is that part of the rehabilitation alternative’s duration is projected to occur in 40 years.

One question that has arisen often in these seven months – could a new bridge hold West Seattle light rail too? The CBA suggests it could:

Sound Transit’s current plan is to build its own structure for the West Seattle to Ballard Light Rail Extension (WSBLE) However, noting the opportunity for synergy between agencies, this measurable examined the technical feasibility of adding light rail to the WSHB structure, now or before 2032, when it is assumed that the WSBLE would be complete. Coordination between Sound Transit and the City has commenced to determine if a joint structure is desired. To date, Sound Transit and SDOT have discussed:

— Design life
— Capital costs
— Sound Transit O&M cost data
— Geometric considerations (vertical curves)
— Seismic design spectra
— Design loads (any plans for future increase?)

In addition to these discussion topics, SDOT has requested the following items from Sound Transit to support the planning of a replacement structure:

— USCG Navigation Impact Report (NIR)
— Topographic surveys and mapping of the ground and waterway
— Geotechnical information logs and borings
— Environmental reports/studies
— Traffic data, forecasting, and modeling used for the WSBLE DEIS
— Preferred alignment drawings and cross sections
— Anticipated construction schedule
— List of planned temporary and permanent property acquisitions

For the purpose of the CBA, WSP assessed which alternatives could accommodate light rail. Alternatives 1 and 2 do not reconstruct the bridge superstructure until after 2032, while Alternatives 4, 5, and 6 would be able to\ accommodate light rail prior to 2032.

The document reviews a long list of other factors – from broad, such as business and worker impact, noting that businesses may benefit from a captive audience as well as be harmed by the cross-river travel challenges, to technical, such as easements and utilities.

And now, the numbers. Note that one column shows the basic construction costs – the other columns take into account cost factors such as maintenance over whatever the ensuing lifespan is:

Everything above is the result of a quick readthrough, so we could get the document out to you. We will continue reading and add any other toplines. SDOT, meantime, (4:39 pm update) just published its own explanatory post; they write that Options 2 and 4 – repair and superstructure replacement – “rise to the top.” Meantime, tomorrow’s Community Task Force meeting (noon Wednesday; watch here – UPDATED LINK) will include a topline review and discussion; the document was sent to CTF members late last night, and they are expected to finalize their thoughts on it by month’s end. The mayor is now expected to make her recommendation sometime nextd month.

73 Replies to "From eight-digit repair to ten-digit tunnel: Here's the West Seattle Bridge Cost-Benefit Analysis"

  • Goldendog October 20, 2020 (4:30 pm)

    Cliff notes available 

    • WSB October 20, 2020 (4:41 pm)

      The SDOT post went live minutes after ours – we’ve added the link above.

  • Joe Z October 20, 2020 (4:33 pm)

    The West Seattle coyote saw its shadow today–that means 6 more years of detours! Grabbing some popcorn and looking forward to the comments section. 

    • DAFFY October 20, 2020 (6:06 pm)

      Bravo Joe Z!  Best laugh of the month.  Thanks.

  • Jort October 20, 2020 (4:37 pm)

    $1.9 billion for the magical unicorn pony tunnel?! That’s 171 percent of the TOTAL annual capital budget for the entire city of Seattle. Guess what?! NO TUNNEL. It was fun while it lasted, amirite?

    • Frog October 20, 2020 (5:09 pm)

      Dude, you have no imagination.  After Biden wins, there will be literally three trillion dollars raining down on the land.  A couple of bil for a tunnel is peanuts.  We can have that, and an equestrian / bicycle bridge, and ponies too.

    • junctioneer October 20, 2020 (5:11 pm)

      I can’t believe they ever wasted their time considering that option. I guess that’s what happens when the people of WS demand an option they know nothing about.

      • Jort October 20, 2020 (7:37 pm)

        If you can’t believe that the city would waste time and money trying to satisfy the insatiable curiosity of mostly well-meaning but overwhelmingly uninformed citizens who pester officials incessantly about trivial magic wish-list items because they and their neighbors all agree with each other that they think it’s a good idea and so do their friends who post internet comments so why don’t we just do it … then you haven’t lived in Seattle very long. This is called the Seattle Process and it is the defining feature of our governance. 

        • Peter October 20, 2020 (10:07 pm)

          Please propose what you would prefer in terms of process, what degree of replacement you prefer, and who you believe should make all decisions if your preferred solution is not followed.

          • KM October 21, 2020 (7:22 am)

            More Seattle Process, please!

          • junctioneer October 21, 2020 (11:36 am)

            That’s exactly it–I don’t want to direct which of my “preferences” get looked into. I think it’s ridiculous that some far-out radical project got considered in order to appease well-intentioned by uninformed people. This is exemplified by the completely inaccurate survey sent out by Herbold.

    • Jeff October 20, 2020 (5:21 pm)

      No kidding, hopefully we can finally put that to bed.  

    • Peter October 20, 2020 (6:40 pm)

      Fact is, people in West Seattle really want great infrastructure, they just don’t want to see it or pay for it. 

  • Time to fix the bridge! October 20, 2020 (4:51 pm)

    $47 million to get the bridge reopened and have it fulfill its life expectancy is a no brainer. It’s really not even capital costs, it’s deferred maintenance come due! 

    • drew October 20, 2020 (9:17 pm)

      Omg, this is  so true! Bridge Closure due to delyaed maintenance. Repairs will take at least 2 years to complete. The city of Seattle takes accountability and apologizes for it’s negligence.

    • L October 21, 2020 (7:59 am)

      Agreed.   Spend the $47 million to repair.   We also know that any estimates to replace are grossly understated in terms of dollars and time.   I can’t figure out why the city is so hell-bent on replacement other than they’re incompetent, because the answer seems so blatantly obvious.  Does the replacement “cost” include the costs to residents of not having a bridge for at least 4 additional years?   REPAIR!!

      • JVP October 21, 2020 (4:17 pm)

        SDOT wants a shiny new toy. Think how fun it would be for them to oversee a mega project!  If you were in their shoes, wouldn’t you want the fancy new bridge? Repair and maintenance ain’t glamourous. Fortunately, SDOT staffers don’t make the decision. 

  • AMD October 20, 2020 (4:52 pm)

    OMG, please no tunnel.  There is no reason this needs to be a tunnel.

  • Grant Nguyen October 20, 2020 (5:02 pm)

    Reading between the lines, seems like Alternative 2 (Shoring through 2022 + replacement in 2062) is the winner, particularly when reading through the sensitivity analyses (especially analyses 1, applying the industry-standard discount rate for costs, and 2, re-analysing for a 15-year repair lifespan vs. 40). WSP also seemed very adamant/optimistic about being able to achieve a 40-year lifespan with Alternative 2 (while noting that they did build in/quantify an early-failure risk), which I found interesting. 

    • Matt P October 20, 2020 (7:52 pm)

      I hope you’re right.  Repair and back by 2022 would seem like the dream scenario from how bag it looked in March.

  • skeeter October 20, 2020 (5:04 pm)

    I really only have two questions:1.  WWJD?  (What would Jort do?)  I’ve come to trust Jort’s keen insight and understanding of the transportation challenges we face  and I’d like to hear what option Jort thinks is best.2. This evening is the official reveal of the GMC electric Hummer with 1,000 horsepower.  I plan to reserve my spot when the order banks go live during the World Series tonight.  Will the bridge be open by December 2021 when my new truck arrives?  

    • Anne October 20, 2020 (7:58 pm)

      Oh please.are you serious?

  • Time to fix the bridge! October 20, 2020 (5:07 pm)

    $47 million to repair the bridge and restore its full life expectancy seems like a no brainer! And it’s hard to even call it a “capital” expense, it’s really deferred maintenance. 

    • Jon Wright October 20, 2020 (6:40 pm)

      I agree, but I think the big variable is they aren’t 100% certain it will last the full 40 years. If it was 40 years for sure, absolutely. But maybe 40 years? Not as sure. The intriguing thing about a new bridge is if it could combine motor vehicle and light rail traffic. But the prospect of staring at a closed bridge sitting there for 2 years before construction of a new bridge even start while planning, EIS, and permitting happens would be unbearable.

      • sna October 20, 2020 (7:32 pm)

        WSP says 95% chance repairs last 40 years, according to Seattletimes.  SDOT is being more pessimistic, but don’t know if that’s based on anything other than CYA

        • Neighbor October 21, 2020 (9:56 am)

          Perhaps WSP assumes that someone’s going to maintain it properly, and SDOT knows they won’t.

  • Bugsy October 20, 2020 (5:16 pm)

    Can anyone explain this to me? It seems like this is saying that the closure duration would be the same for repair as it would be for replace?  How could that be the case?  With repair, we would be back on the bridge in 2022.  With replace, who knows when.  So, the traffic in the detour routes would go on much, much longer wit replace.  What am I missing?

    From the CBA: “The continued closure causes increased vehicular traffic using detour routes through marginalized communities. Because the overall closure duration was similar for Alternatives 2, 4, and 5 (even if in two phases), these were rated as better than Alternative 1, which would require two closures totaling 7.5 years, or Alternative 6, which would require one closure totaling 9 years.For this measurable, rehabilitate and replace (except Alternative 6) have similar outcomes – the only difference is that part of the rehabilitation alternative’s duration is projected to occur in 40 years.”

    • WSB October 20, 2020 (5:35 pm)

      Because they are counting a future closure that would be needed someday to replace the bridge.

    • Chemist October 20, 2020 (7:26 pm)

      Unlike most highway projects (new overpasses, the spokane viaduct replacement, etc) where they build the new structure adjacent and then connect it to minimize closure times, SDOT and WSP figure that the replacement bridge has to be built where the current high bridge is now and so it’ll need to be torn down before construction can start.  I’m not sure exactly why a new bridge can’t be built to the north of the low bridge, to be honest.

      • JVP October 21, 2020 (4:22 pm)

        They really need to use discount “rates” on the future closure. What’s the present value of the future closure? 4 years closed today is more painful and costly than 4 years closed 40 years in the future. 

      • Nick October 21, 2020 (6:20 pm)

        Building the the north impacts the coveted port traffic. Thats a non starter to them. 

  • Joey October 20, 2020 (5:20 pm)

    $47M for repairs that can be completed by 2022 and projected to last 40 years. No further reading or debate needed. Let’s go! 

    • Bugsy October 20, 2020 (7:28 pm)

      I agree completely.  That’s the ONLY option worth considering.

      • Admiralty October 20, 2020 (8:40 pm)

        Repair is the only viable option. Economic damage to wait more years for anything else is not worth it. SDOT refuses to say what closure is costing us daily, monthly, annually.

        • WSB October 20, 2020 (9:11 pm)

          Actually the CBA does include some of those cost estimates. See page 45, “business and workforce impacts.”

  • TJ October 20, 2020 (5:28 pm)

    I for once agree with Jort. Tunnels off the table 

  • John October 20, 2020 (5:38 pm)

    Sound Transit is planning on building their own bridge?

    Must have deep pockets (taxes) to do that.

  • Mj October 20, 2020 (5:59 pm)

    The repair option is the clear choice.  With an aggressive schedule I believe it could be done by next Fall!

    Ps: I have a 1st, I agree with Jort the tunnel fantasy is off the table

  • 40years October 20, 2020 (6:12 pm)

    This is such a no brainer – Seattle will choose to not use a brain. Most dysfunctional city in America = Seattle, WA. Liberal Alabama. Fix the bridge. I mean…come on. Fix it. 

  • David October 20, 2020 (6:18 pm)

    Repair is the clear winner. No other way to see this in my opinion, but leave it up to seattle gov’t and who knows what is on the table. 

  • BBILL October 20, 2020 (6:27 pm)

    That “cheap” repair isn’t looking so cheap: “Alternative 2 operations and maintenance costs are $40.5M, nearly double
    that of Alternative 4 at $22.1M. Repair and rehabilitation costs for
    Alternative 2 are $1,279.8M versus $247.3M. “

    • Sna October 20, 2020 (7:35 pm)

      The repair is 47M up front.  The total cost for option 2 is super expensive because it includes the cost of a new bridge in 2060.  So that number is the cost of repair AND replacing.  

      • BBILL October 20, 2020 (8:00 pm)

        Yes, once it’s recognized that the broken bridge needs to be replaced, and there is risk that a repair would not make it until 2060, replacing today avoids the continuous high maintenance cost of Alternative 2.

  • Don Brubeck October 20, 2020 (7:33 pm)

    This study shows the fallacy of infatuation with technology and speed. The Immersed Tunnel scheme, like the existing failed bridge that was
    overly innovative in it’s time and rushed to completion, was enticing
    but very costly. It is more important to look at actual conditions of the whole route; allow time for analysis and design;  consider the real needs of the community; and use time-tested, durable technology. 

    • dsa October 20, 2020 (9:55 pm)

      Don, what you wrote is the most sensible thing I’ve seen written here or by the city.” use time-tested, durable technology.”

  • Matt P October 20, 2020 (7:45 pm)

    There is no question.  2 or 5.  4 may be “faster” in that it doesn’t need an additional closerure in the future for replacement, but that’s completely disingenuous.  The repair option gets us back in 2022 with a closure somewhere 5 to 40 years in the future and the replace superstructure in 2026.  No one would choose option 4 just because option 2 will require replacement some time in the future and could possibly be done once the light rail is here.  If we’re going to replace, then #5 is the no brainer. Possibly faster than #4, safer and will last longer into the future. 
    If we’re going to spend the money, then spend a little more to do it right, otherwise fix the thing cheap and take our chances it will last the 40 years.

  • old timer October 20, 2020 (7:58 pm)

    Repair alternatives may “rise to the top” because SDOT and the City are feeling pressure for a quick and easy solution.  Taxpayers however are looking at not only repairing a faulty bridge, but building a new one for Sound Transit/Light rail.  Can’t the two needs be combined?  And while I am ranting, just where does a tunnel let traffic come to the surface?  Trying to imagine commutes to Admiral, Alaska Junction, Westwood.

  • WS October 20, 2020 (8:34 pm)

    OLD TIMER-I don’t want to spend at least 6 years without the bridge just because of the light rail. Build another structure for the light rail as was planned before. And I am a taxpayer too. 

  • Smittytheclown October 20, 2020 (8:45 pm)

    Git r done!  For only 47m!  Woot!

  • Mr C Vu October 20, 2020 (8:46 pm)

    Old timer you got there first I totally agree.
    As usual thanks WSB for the TLDR version. Encouraged that WSP was behind the analysis so my previous concern over conflict of interest is greatly alleviated. This seems to be more about getting City administration on board than anything. They want reliable forecasts for future maintenance costs and guaranteed funding for repair/replace. $40m is something rest of city can swallow. The radically lower up front cost and SHORT time to get the peninsula reconnected should make this a no brainer for the mayor. Can we just repair this thing already and  then figure out a hybrid sound transit SDOT bridge replacement that’s off alignment to calm the SDOT admin concerns and give everyone what they really want? 

  • Beanie October 20, 2020 (8:52 pm)

    Thanks you WSB for the summary!

  • West Seattle Lurker October 20, 2020 (9:43 pm)

    This line from The Seattle Times article caught my attention, Zimbabwe warned a volunteer task force last week to not take the figures literally, because the project is at “0% design.”

  • Steve October 20, 2020 (9:59 pm)

    Why combine light rail with traffic and put all our eggs in one basket again? Keep them on separate bridges so our future generations don’t have to be on an island after an earthquake damages whatever we leave them. 

    • JVP October 21, 2020 (5:40 pm)

      This is a good point you make. Redundant and multi-modal transportation systems are always an important thing to have. 

  • Phil Tavel October 21, 2020 (1:04 am)

    Repair the bridge before the end of 2021 and do it as cost effectively and intelligentlet as possible. That’s it!

  • Amrakx October 21, 2020 (6:46 am)

    I vote for Alternative 2.  

  • sna October 21, 2020 (7:34 am)

    SCC Insight has a great analysis of the CBA that I would recommend all read:

    Summary from SCC Insight: So what’s the big takeaway from the report?  It’s clear that there are two alternatives that rise to the top: Alternative 2 (repair by adding new strengthening tendons), and Alternative 4 (replacing the superstructure). One requires a replacement in 40 years, the other in 50-75 years. Funding will be a challenge for all the options, but Alternative 2 requires the least up-front funding. All of the options require significant dedicated resources for ongoing operations and maintenance, however, and that’s something the city isn’t good at budgeting for.One gets the sense reading the report that the writers perhaps threw some shade on Alternative 2 in order to avoid presenting a clear and obvious conclusion on whether to repair or replace the West Seattle Bridge — and thus evade a political fight. But a close read of the details leads to the inevitable conclusion that Alternative 2, repairing the bridge, is the best option. It’s the most affordable now, and most likely gives the city 40 years to plan and fund a full replacement. It gets traffic moving across the bridge two years from now, minimizing the mobility, workforce, environmental, and equity impacts of the current situation. The work is fairly well understood now, and assuming the fix to “un-stick” Pier 18 goes well in the next few weeks, there shouldn’t be major impediments. There are certainly some risks, including that the repair may not extend the bridge’s life for as long as is hoped, or that a new problem may be uncovered. But at this point there are no insurmountable obstacles to moving forward with repairing the bridge — and that’s a much-needed piece of good news.

  • H October 21, 2020 (8:30 am)

    All – It is apparent that the city is steamrolling towards a repair option that is more expensive, more uncertain, and will cripple us at least through 2026.     This is unacceptable.   Time to write your elected officials to promote the repair – this goes to all the councilmembers I believe. 

    • H October 21, 2020 (10:14 am)

      I meant steamrolling towards a REPLACE option … repair the bridge now!

  • shotinthefoot October 21, 2020 (8:56 am)

    I must have missed the pricing for the zipline from Pigeon Point to downtown – was that not an option discussed? 

    • Dan October 21, 2020 (2:58 pm)

      Issues with the FAA! :-)

  • mc October 21, 2020 (9:11 am)

    Any choice but the immediate repair of our bridge is irresponsible. Don’t sentence our community to a slow death. REPAIR THE BRIDGE NOW! 

  • Stuck in Traffic October 21, 2020 (9:16 am)

    Repair it now… what else is there to discuss? FIX IT NOW!  After it reopens to traffic… Then and only then can you start discussing new bridges and new tunnels and whether the Light Rail can be on it etc. Get it Done!

  • wetone October 21, 2020 (9:30 am)

    I agree with many that #2 looks best with info we have at this time. What I really want now is an outside look into how we got here and why nothing was done from 2013 till shut down. ” Accountability  ”  for some reason  Seattle government has a huge problem with this and until this changes I have little faith with anything they say. 

  • sw October 21, 2020 (10:42 am)

    Option #2, all day long.  With the pandemic and other issues the city and nation are currently facing, funding for even the repair will be a stretch – let alone the full replacement cost.  I’m not usually one to promote band-aid solutions, but the estimation of up to 40 year lifespan for the fix changes things.  It would be ridiculous to design two new bridges (assuming Sound Transit would continue to develop their own bridge).  The repair option gives the city and ST time to work together on a long-term single bridge solution and do themselves both a favor by splitting the cost.  

  • Kyle October 21, 2020 (10:57 am)

    Now that we actually have Herbold going to post another unscientific survey? At least now we have some data :). As for my vote, #2 is the winner. 

  • Ex-Westwood Resident October 21, 2020 (11:01 am)

    Option #2.
    Who knows, by the time it actually needs to be replaced, in 40 years, we may really have “flying cars” and have no need for roads or bridges as we know them today. 

  • drahcir61 October 21, 2020 (11:09 am)

    Horse & buggy!
    Horse & buggy!
    Horse & buggy!

    Sorry, watching too much Masterpiece these days.

  • Stuck on Roxbury October 21, 2020 (12:01 pm)

    What about that I cannot sell my house or move without significant loss since I live on Roxbury and have 20 car back-ups in front of my house that no fool would buy and that I have to wait long times to get out of my driveway. I cannot wait 6 years or more for a replacement that will continue to drag the value of my house down.

  • Mj October 21, 2020 (4:14 pm)

    The $47 million repair cost is simply the cost of SDoT’s deferred maintenance, it’s time to get the repair work underway.  AND hopefully the City and SDoT will finally prioritize maintenance over sexy new projects and other City spending.

  • Paul Tralb October 24, 2020 (4:26 pm)


  • WSB October 26, 2020 (9:10 pm)

    SDOT sent a link today to 628 pages of appendices – added above but also noting here for the archives:

    • Chemist October 26, 2020 (10:03 pm)

      Thank you.  I’d wondered why their website had omitted the appendices.

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