At last week’s Sound Transit Board meeting, Sound Transit’s West Seattle project manager Brad Owen showed the extend of the guideway from the SODO station along the Spokane viaduct, across Highway 99 to the Duwamish bridge. He explained that rather than pouring its concrete deck in place, they plan to use precast segments. That will speed up the process and reduce cost.

The rendering shows the enormity of the guideway, adding a 4th level to the existing 3 levels (at grade, Spokane viaduct, Highway 99). At least the underside would be a bit nicer than the i-beam girders Sound Transit has been using lately along I-5.

Sound Transit has been using precast box girder segments in the past such as in Tukwila:

Both i-beams and precast segments have originally been developed for highway construction.

While assembling segments is faster than in-place construction, in Malaysia they precast full segments between towers. Then you don’t need a bridge between two towers for installation but a crane or two. That speeds up installation. Instead of a structural box underneath, they use two U-trough girder segments, one for each track. As the U wraps around the wheels, any rail noise is contained within the concrete trough. As the sides of the segment are at door level, during an evacuation from one train to another the center can help riders to get across to the other train without a major gap.

The latest guideways for the Grand Paris Express line use segmented box girders too. For roads the box must be under the deck, but for Line 17 they put the box above the deck to help with evacuations. This allows the bottom of the guideway to be totally flat. With slender towers it creates the most stunning elevated urban guideway design I have seen thus far.

If Sound Transit would build guideways that way, I bet people would be even more supportive of allowing elevated lines through the urban core.

44 Replies to “SODO guideway construction”

  1. As cool as the technique is, I do have some concern about installing them across SODO. The streets there have obvious unevenness due to the poorer soil quality underneath. Consider too that we just witnessed a huge West Seattle Bridge crisis thanks to problems with the way it sits on the ground.

    I’m not a structural engineer but it seems to me that sleekness shouldn’t be a primary objective in building this segment.

  2. I don’t believe that delivering pre-cut sections of superstructure is new for ST. I watched that method, over the course of over a year, for Angle Lake.

    My big complaint is the lack of interest at ST in building a carbon-negative concrete plant, as part of a joint venture with other local governments, and the state. It took the cooperative efforts of a bunch of authorities to build the windmill farms. They now need to use the same sort of cooperation to de-carbonize the ST3 capital construction process, as well as sell the carbrete to private builders throughout the region. ST3 needs to help reduce the impact act of climate change, not use up a big chunk of humanity’s remaining carbon budget.

    1. A very good point. I have been looking for years for projects that would move to a lower carbon concrete but I never hear of a major project implementing this.

    2. I think the problem is that it would have to be a state agency since the plant would have interests in providing concrete to public and private (mostly private) builders, but the last time the state tried to become a commodity producer, the WPPSS became the WHOOPS.

    3. ST’s mandate is to provide regional transit, not to fix the concrete-production process. Some people are already annoyed that ST is selling surplus construction land below market rate for affordable housing. This would be another of those, at a time when ST is having trouble affording its voter-approved project.

      The state should take the lead on this, since it’s the highest level of government, has a wide-ranging mandate, and has the most authority and resources and taxing ability. Just like the state could buy the BNSF track and make it passenger-priority and shift freight to UP and build more passenger tracks, it could help set up a carbon-negative concrete plant, and a state infrastructure bank while it’s at it.

  3. As I’m looking through the presentation, I’m seeing a statement: “Provides cost savings from reduction … in vertical transportation elements.”

    This is a high volume transfer station. This isn’t the place to reduce vertical transportation elements.

    This skimping in vertical transportation continues to plague the culture at ST. Why does ST keep spending extra billions yet skimp on vertical elements to save a few million?

      1. Not having escalators increases travel time for a rider. A cross platform transfer can reduce the transfer time by 1-2 minutes depending on the health of the rider and condition of vertical devices. Since the average wait is have the train frequency, that’s like having trains run 2-4 minutes more often.

        So having a cross platform transfer is like having trains run frequencies drop from 12 minutes to 8-10 minutes.

        That’s basic math. That’s not an opinion.

      3. Sure, but are we actually getting better frequency by skimping on vertical conveyances?

      4. “Sure, but are we actually getting better frequency by skimping on vertical conveyances?”

        No. The cost of vertical conveyancers ($6-12M each) is well under the cost of merely buying one more four-car train ($17M). And one more four-car train will only reduce frequency by less than a minute.

        Keep in mind too that ST forecasts more riders transferring at SODO than they forecast boarding at a majority of ST Link stations. And many of the SODO transfers will be riders from Capitol Hill, UW, North Seattle and Snohomish headed to SeaTac with luggage ( now the second busiest station).

    2. The transfers won’t just be from west to south and south to west, but also going in the same direction, to avoid the long transfer paths at Pioneer Square -ish and Westlake.

      Indeed, SODO could end up handling the most downtown transfers. Lots of elevators along or within the (center?) platform would be cheaper than threading the lines to create all possible cross-platform transfers.

      1. Certainly the center platform will get twice the number of transfers. However, it only takes on out of service escalator to end up making a ride walk down three floors of steps or wait for an elevator that may be out of service.

      2. Consider just how much of the transfers will likely happen at SODO:

        * NorthSpine-SouthSpine (probable the most common transfer)

        * WestSeattle – Ballard

        * WestSeattle – SourhSpine

        That is three of the seven downtown line transfer pairings.

        Good gosh they will need more elevators than a typical station.

    3. Yes, construction and maintenance cost could vastly be reduced by using a single track with a single center platform instead of three platforms as currently proposed. Instead of three sets of vertical transportations, you would only need two. Vertical transportation usage (and therefore maintenance) would be vastly lower, due to a simple cross-platform transfers rather than having to traverse two escalators for most transfers.

      1. Thanks, Martin. It’s glad to hear someone else note that there will be only ten tph at the max on Line 1 and six on Line 3. Now sixteen doesn’t divide evenly into 60, but the result would be a train every three minutes and forty-five seconds.

        That’s often enough to require overpasses at Lander and Holgate, and closing Lower Royal Brougham just east of the tracks. But ST has already committed to the two grade separations to accommodate an independent trackage WSLE, AND Lower Royal Brougham doesn’t get much traffic at all.

        There is no reason in the world to waste a billion dollars building another set of tracks for six trains per hour in each direction.

        Of course, the real question is, “Who still thinks that West Seattle Link is a good idea at five to seven billion dollars?”

      2. To be clear, the 10 and 6 are one direction only. That summed (16) is what each shared platform would serve.

        However if we count train arrivals in either platform it’s 32 arriving trains per hour.

        It’s just a semantics comment. Certainly a single platform could accommodate both lines at SODO — and it would reduce walking when transferring. You would just hop off one train and wait for the next train running in the other line. No need to use any stairs, elevators or escalators.

        Relatedly, the presentation talks about a “shoo fly” but the location for the crossover are actually not shown.. A shoo fly is a temporary crossover track and the switch to connect it to the permanent line. It appears that ST wants to build the station platforms in stages, and put 1 Line trains into the 3 Line track to serve the station in the construction phasing.

        Note that the presentation diagrams don’t show the actual shoo fly location. They just say there will be one.

        The new shoo fly proposal here to me just demonstrates how this station has the opportunity to be built with less than two side platforms as well as a center platform. If they are going to close the existing platforms anyway, why not propose two sets of vertical treatments rather than three, or one shared platform in each direction?

        I seems to me that the assumptions about the SODO station layout and construction phasing are just revealing how the staff — in their steadfast defense of the original three platform layout — have dug their heels in rather than to see that the station can be more user friendly to handle the high volumes of transferring that they project will happen at SODO, and fully rethink the station layout.

      3. Of course sixteen trains per hour is in each direction. I don’t see that that is a problem, though. There will be almost no “walk-up” ridership, but there will be people accessing the platform(s) from buses. So, sure, have a platform on the east side of the station as well. Riders headed north — certainly the majority of transfers from the buses — will have a level transfer, and its in the “to work and activities” direction that rapidity is more important.

        Are you worried that a single platform won’t be large enough for the number of passengers that would use it? Well, then, make it wider. There’s no reason that the northbound track has to stay where it is. Maybe a couple of the power transmission poles would have to be moved eastward also, but, really, how hard can that be?

      4. “There’s no reason that the northbound track has to stay where it is.”

        That’s exactly right Tom!

        I see this new proposal to have a shoo fly to a different platform during construction as flying in the face of ST’s prior decision to not move any existing platform at SODO. They could totally design the station differently if they wanted to by using this recent shoo fly concept.

        Any other system would say “oh we can reduce the number of riders on escalators” or “we can eliminate transferring riders from even having to use an escalator” or “we can have two sets of escalators rather than three” when using a shoo fly to a different platform during construction. But not ST!

        Dagnabit someone at Sat wants three different platforms at SODO and won’t settle for any fewer!

  4. I have an idea I think having up above until it hits delridge and then I think they should have it the stations go on under the neighborhood residential so without tearing down any homes and properties to make people happy my opinion is I think they should have it underground but haven’t going over the or by the West Seattle bridge is a good idea like the picture you guys will show what this is my idea I think the stations and the guideway should be a tunnel after you hit delridge having sleep down into a tunnel??..

    1. That’s the current $5 billion plan. WSLE will be elevated from SoDo to Delridge — actually a bit farther to the freeway behind the steel mill — at-grade alongside the freeway to the top of the hill and then enter a tunnel. Thank you for summarizing it for other new readers.

      You might want to use one of those two periods you saved up for the end somewhere in the middle of your ninety-nine word sentence when you explain it to them, though.

      3. And the voter-approved plan was all elevated. The estimates and the financial plan were pinned to that configuration. Adding a much higher bridge and a tunnel with underground stations are significant scope additions that drove costs up and were not part of the deal the public signed up for. And since it’s new scope without new revenue to pay for it, proceeding with the current configuration puts the overall program at grave risk.

  5. Regarding, “SODO guideway construction”, nice article. I really hate to be that guy, but “enormity” does not mean “enormous” – it means very bad or wicked.

    1. It has multiple meanings. Look at the third meaning here: https://www.merriam-webster.com/dictionary/enormity. It is quite reasonable to use it in this case as the author is suggesting that not only is it huge, but there is a negative aspect to it’s size. It is huge, costly and not especially attractive. It is not like, say, Mount Rainier (which only fits the one definition — it’s really big).

    4. I’m going with Martin on this one, as in “The West Seattle Link Extension is an enormity warping all sense of scale and probity.”

    1. If you want an even better view, you might as well build a gondola over Pigeon Point for a fraction of the price of the WSLE. Enjoy Mt Rainier on one side and the Needle on the other side and get a much higher frequency and transfer experience. 😉

  7. West Seattle Link is a pretty terrible project on cost/benefit.

    Still seems tragic that this will be built before light rail to South Lake Union. Especially when it will provide worse service than the existing buses.

    Surely Dow should keep calling the shots…..

    1. I looked up the existing bus routes on Google Maps and I’m so confused as to why this multibillion dollar project is getting top priority…current trips from West Seattle to downtown only take about 20 minutes. Am I missing something here?

      1. It’s easier to understand once you realize Link is more than just a light rail line.

      2. Susan, it’s because a few elected leaders were playing a board game in 2016 called “Expanding Link” that was really called ST3. But rather than look at adult things like travel time savings and cost-benefit ratios, the leaders did what a first grader does and just started drawing lines on a map to the places they personally wanted to see and possibly to make buddies associates and campaign contributors happy. And the people who developed station locations also did skimpy track snd station costing.

      3. I’m going to pile on here a bit. The basic problem is that the board does not understand transit fundamentals. The particular problems with West Seattle Link stem from that. The board treats Link light rail extensions like community centers. They assume they are fundamentally valuable wherever you put them and there is no real alternative. Thus you want to spread them around, covering as much of the city and region as possible. Unfortunately transit doesn’t work that way. Light rail is simply an alternative to buses (and other forms of transit). It is much better than buses in some cases and worse in others. It can provide a tremendous improvement in the transit network in some cases and do very little in others.

        Thus West Seattle Link — like Everett, Tacoma and Issaquah Link — was largely chosen based on regionalism. It was if they looked at a map and decided to sprinkle a little Link here and there. West Seattle is extremely well suited for Open BRT* and an extremely poor choice for light rail. To simply add one station to West Seattle Link costs a massive amount of money while adding very little. Open BRT would be much cheaper and better for many riders (https://seattletransitblog.com/2024/06/07/west-seattle-by-bus-instead-of-light-rail/). But BRT for West Seattle was never seriously considered.

        Regionalism also played a part in prioritizing West Seattle Link. Even if you assume that Link is the best long term option for West Seattle it does not at all seem obvious that it should be included in this package. Consider some alternatives. The Metro 7 has very high all-day ridership and fairly slow travel speeds. It travels over relatively flat terrain — well suited for cut and cover or fairly low (inexpensive) elevated rail. But that wasn’t even considered because “Rainier Valley already has light rail”. A similar case can be made — by looking at data that Sound Transit itself gathered — that the two best projects (of those studied by ST) are Ballard to the UW and Ballard to downtown. But that would mean “too much for Ballard”. They wanted to spread the Link around. They wanted to give the impression that huge swaths of the city would benefit from Link (instead of huge numbers of people) and thus West Seattle Link became part of ST3.

        It isn’t clear why West Seattle Link was placed in front of Ballard Link. Ballard Link is more expensive and for financial reasons it makes sense to build the cheaper projects sooner. The problem with that argument is that the downtown tunnel was arbitrarily considered part of Ballard Link. Ballard to Westlake is probably not a lot more expensive than West Seattle to SoDo — even though it is much more useful. I think it was assumed that West Seattle Link — though expensive — was considered “the easy project”. There are only three stations. It was not considered that expensive or that risky. There was not that much debate as to the particulars (prior to the ST3 vote). One theory is that Dow Constantine (who is from West Seattle) wanted it done first. It is fairly common for large projects to not be completed — thus it is quite possible that West Seattle Link will be built while we run out of money for Ballard Link.

        * I am reminded of this essay written by Jarrett Walker https://humantransit.org/2009/11/brisbane-bus-rapid-transit-soars.html and this particular section:

        The most common question is “if you’re going to build all that infrastructure, why not just put rails on it? Answer: Because Brisbane, like Portland, has a single very strong downtown but no major centers of activity outside of it. For that reason, the demand pattern spreads out as you go out from the city, and the route network spreads out to follow it. So the high frequency through this inner busway segment is made of routes that branch out to serve several different corridors further out, without requiring a connection.

        I think that actually describes West Seattle Link much better than it describes Portland (or Seattle in general). The demand pattern is well suited for buses that converge onto an expressway that can then run express to Downtown Seattle.

      4. “It isn’t clear why West Seattle Link was placed in front of Ballard Link.”

        I remember at the time it was because West Seattle Link did not have any underground segments, so ST said that they could get it open sooner.

        And anyone following the decisions afterwards knows how ridiculous if not deceitful this logic was.

  8. Regarding pre-cast segments…ST used them for the initial segment to Tukwila as a means of expediting delivery. However, they eventually gravitated back toward using beams because they are cheaper and less complex to fabricate and install. So color me skeptical that pre-cast segments will be cheaper. The main reasons are scaling fabrication — you need a supplier who can deliver the product; customized design — to handle changes in grades and curves, the segments are often unique, like puzzle pieces and require specialized design which can drive up unit costs; and transportation– the precast segments for Tukwila were built in Cashmere, and trucked across Stevens Pass one at a time. That is a whole lot of baked in cost. So, pre-cast segmental construction in summary: faster, yes; cheaper, no. Footnote: they can also be more seismically resilient due to the post-tensioning used to hold them in place.

    1. “trucked across Stevens Pass one at a time”
      wow, that’s a lot of added carbon

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