Page Two articles are from our reader community.

Both transit advocates and politicians have been discussing the idea of a second downtown tunnel through Seattle. The tunnel would act as the foundation for future rail service to Ballard and West Seattle. Seattle Subway’s proposal currently looks like this and seeks to address a few issues:

  • Mitigates the closing (for buses) of the current Downtown Seattle Transit Tunnel by building the tunnel initially for buses
  • Provides capacity enhancements in the downtown core
  • Can provide exclusive lanes for buses heading to West Seattle and Ballard

The proposed tunnel could also have a few drawbacks:

  • Costs of unused railway infrastructure: If the tunnel were to be built initially with railway infrastructure (tracks, power and communications) as Seattle Subway suggests, these would still require some form of maintenance even if they were not being used. These infrastructure components don’t stand still over time, and will have an aging effect. No one really knows how long it would take for rail services to begin, but it would be a waste to maintain infrastructure that is not being used.
  • There are only 3 stations (Westlake, Madison and International District), fewer than the current DSTT. Although this would give a direct connection to Madison BRT, it would also mean that buses serving the new tunnel have farther stop spacing and potentially shorter travel times than light rail in the DSTT, the opposite of what it should be.
  • Conversion to rail could be a slow process due to institutional and political inertia, which may result in another DSTT situation where buses are “phased out”. The lesson to be learned from the DSTT, is that joint-operations is difficult and results in unreliable service for every mode, even six years into operations.
  • Alignment constraint in the current DSTT are not addressed, such as the Westlake or Chinatown curves

In an attempt to explore how these issues could be resolved, I’ve created another proposal, which is a tunnel on 4th Ave that will accommodate all light rail services from the beginning and in the future. The current DSTT will then serve buses (again) and potentially streetcars. The “Westlake curve” will also be removed, allowing higher speeds in the tunnel. Here are the key advantages of this proposal:

  • Removes infrastructure constraints from the network: The current DSTT has a few limitations on speed and acceleration. One is the horizontal shift in the rails before and after the platforms. The others are the tight curves just south of Westlake and International District. With a new tunnel, Sound Transit can take advantage of the (rare) opportunity to remove those limitations by designing a large-radius curve between University St and Capitol Hill, while using better transitions before/after the stations. This will allow for higher travel speeds through Downtown Seattle. This also removes one of the infrastructure constraints that prevents Sound Transit from purchasing higher-capacity non-articulated vehicles, such as those on standard subway systems.
  • Immediate travel time and capacity improvements for the entire regional light rail network: With infrastructure limitations removed and stops modified, higher travel speeds through Downtown Seattle will not just improve local travel time, but regional travel time. Both Central Link and East Link stand to gain a few minutes, along with reliability improvements. With higher stop spacing, punctuality and faster travel times, the capacity of the tunnel can also be increased to accommodate trains from additional lines. Converging multiple lines in one city center tunnel will provide a very high-frequency service through downtown
  • More leverage for regional funding: The prospects of regional funding for a tunnel that will, at its beginning, only serve Seattle routes will be a tough sell. However, if it can be used by regional rail in the beginning (Central Link and East Link), and provide travel time/frequency improvements on opening day, there could be more leverage to ask for improvements.
  • Separation of operations from day one: Dedicating the new tunnel to rail on opening day will prevent a repeat of DSTT. Joint-operations doesn’t work for a variety of reasons, but the basic concept is that rail operations are completely different from bus operations. Rail involves one large vehicle regulated by signals, occupying a section of the track at a time as it travels through the tunnel. Bus operations involve several vehicles, arriving and departing at various times. This has the potential to occupy multiple sections of track simultaneously, delaying service behind it. Providing a separation from day one will avoid this situation.
  • DSTT can serve both buses and streetcars: DSTT rail infrastructure could be converted to serve streetcars. Joint operations for streetcars and buses would be more compatible than light rail and buses, as their operation philosophy is mostly similar (short vehicles that can operate in mixed traffic without dedicated signalling systems). Some modifications will have to be made. This includes extending the width of the platforms by about 3 inches to accommodate the narrower streetcars, but the floor height is roughly the same (355 mm for Link and 350 for Seattle’s streetcars). Streetcars will also have to be capable of running at 1500 V DC in the tunnel and 750 V DC on the surface, although dual-mode operations are not uncommon elsewhere in the world.

Of course, no proposal is without drawbacks:

  • The most obvious drawback is that Central Link and East Link will skip Westlake Station, which is necessary to provide the large-radius curve between University and Capitol Hill. The good news is that the DSTT will still serve Westlake, and a future light rail extension to Ballard could reintroduce light rail service beneath the current Westlake platforms. Skipping the station also improves travel times for the regional-oriented Central and East Link lines.
  • Construction impacts when service is transitioned to the new tunnel
  • Bus and streetcar services in the DSTT depends on the fate of the Convention Place Station, and whether access to the DSTT will be preserved after its expansion. If not, a new access point will have to be built.

Comments? Ideas? Share your thoughts below!

25 Replies to “New downtown tunnel for light rail, current one for buses and streetcars”

  1. A couple of things:

    1. How does this interface with Madison BRT? Maybe add a stop at Madison in one of the tunnels?

    2. What about building a link between the current DSTT to the two branches that go to Aurora/SLU and LQA/Ballard so buses can use them and when the time comes, the two branches can easily be switched over to rail use as they will already be connected to the trunk route?

    1. 1. By stopping at the same locations as the current DSTT, it wouldn’t connect well with Madison BRT. However, I would argue that Madison BRT should accommodate the rail network, not the other way around. If a stop was added between University and Pioneer Square, the stop spacing would be too small and add to regional travel times.

      2. If I’m understanding correctly, your proposal would have East/Central Link in the new tunnel and Ballard/West Seattle services in the current DSTT.

      That would be a good idea for buses and maybe even rail. The drawback is that rail service would be split between two tunnels, and you would sacrifice the frequency that would be provided by combining all light rail service into one.

      1. I wasn’t clear on the second point. I meant that all rail should be moved into the new optimized-for-rail 4th avenue tunnel. However, the northern branches of the new tunnel should be accessible by bus until such time it actually makes sense (if ever (demand-wise and financially)) to run trains to West Seattle, Ballard, and SLU (and beyond). At that point, many of the buses will be replaced by rail to the same locations and bus access to the northern branches of the new tunnel can be cut off.

        So what I am suggesting is the WSTT with rail service switched to the segment of the new tunnel that parallels the current DSTT instead of filling it with buses. The northern branches can be accessed from both 3rd and 4th avenue tunnels so until rail makes sense, bus service can use those segments. This improves current rail services and allows for massive reliability improvements for current bus services.

      2. Are you saying to build access for WS buses that would allow them to use the DSTT, connecting into the DSTT between Westlake/University? That would definitely improve reliability for WS buses, and can even be built to accommodate streetcars.

        I also realized that I probably wasn’t clear on my proposal. The initial segment of the 4th Ave tunnel would be between I-5 and IDS, and wouldn’t include the spur off to SLU/QA/Ballard.

  2. How does the new tunnel work on the ID Station to Pioneer Square Station segment? With the BNSF tunnel also to consider, is there room for another tunnel under Jackson Street in that area? With all the tunnel proposals it seems that the portal area around IDS is going to be complicated and then getting to Pioneer Square Station is another very complicated task.

    1. Around Pioneer Square, the BNSF tunnel actually runs between 3rd and 4th. The current DSTT crosses underneath just before Pioneer Square Station.

      IDS is a difficult situation because 4th Ave already acts as a barrier between King St Station and IDS.

      If a new tunnel were to be built, it would have to be either:

      (1) Between 4th Ave and the DSTT, i.e. under Union Station. This is probably impossible…It would involve messing with the foundations of Union Station and 4th Ave.

      (2) East of the DSTT: Which would put it farther away from King St, making transfers more difficult. This would also bring up the question of how to facilitate transfers between King St, IDS and the new tunnel, because IDS station does not have a mezzanine level. Transfers may have to be done by going up to street level, or using an underground passage between the three.

      Without an underground passage, a transfer from King St to the new tunnel would involve crossing both 4th Ave and 5th Ave, which is completely absurd and by no means represents how integrated access should work…

      1. The alignment of the BNSF tunnel is such that there is plenty of room along 4th for a transit tunnel.

        Any tunnel using such an alignment would most likely have a station under 5th. It is really the only place to put an underground station in the area.

        The exact details of connecting to the current DSTT station and the King Street Sounder station would need to be worked out. Connecting directly to the Northbound platform in the DSTT would be easy. Getting to the Southbound platform would require either passengers cross on the surface (even if just the plaza) or digging a pedestrian tunnel under the current DSTT.

        For a number of reasons the connection to the Sounder platforms is likely to continue to require going to the surface and crossing 4th.

  3. 1. You found a way to make the gap between downtown and Capitol Hill stations even bigger! Await a job offer from ST, they love this kind of thing.

    2. Say the Convention Place access point remains. Convention Place is great for buses using the I-5 express lanes, OK for buses using I-5 non-express lanes (e.g. 520 routes) or otherwise using the Stewart-Howell couplet (mostly surface routes to SLU and UW), and painfully out-of-direction for anything bound west of Lake Union. The whole point of a second tunnel is to go places west of Lake Union.

    3. The Convention Place access point is not going to remain. Maybe the new access point will make more sense for buses going west of Lake Union… but that will be hard unless we cut out the Westlake turn entirely and rebuild the station. Maybe we can tunnel all the way to Seattle Center and emerge near the Monorail, creating an Island of Misfit Mass Transit…

    The finance and politics are also pretty challenging compared to the WSTT. We’d have to build one-and-a-half new downtown tunnels instead of one, which is sure to be more expensive. Who pays for the difference? Obviously Snohomish County, since the whole point of doing it this way is to get to Everett faster — it might actually end up a little worse for other riders, depending on how the north end of the refigured DSTT works out. Do Snohomish County voters care?

    Anyway, if you think the curves in the DSTT are bad (they sort of are), at least they exist in service of important stations. From the DBT to the Bellevue tunnel (where we’re building a bunch of sharp curves essentially as the result of political exhaustion) to many aspects of the 520 rebuild, we’re doing stupider stuff without even that as a justification.

    1. I have to agree with Al here. I don’t see the point of building a second rail-only tunnel when the current DSTT should work fine for rail once joint operations end.

      Dropping Westlake station from link (the busiest in the entire system and expected to remain so in 2030) is too much of a price to pay for a smoother curve off of 3rd.

      Furthermore the entire point of a new westside DSTT is to give a place for buses from the south and southwest a place to go along with routes to the northwest. Your proposal doesn’t really solve the north side of that equation.

      I may be wrong but i believe a properly designed tunnel can allow for better joint operations than the current DSTT. This is helped by the fact that fewer trains will be using the tunnel than the current DSTT even once there is a line to both West Seattle and Ballard.

      1. All very good points, which is why I listed the omission of Westlake as a drawback. It’s worth looking into what the service sacrifices would be and it depends a lot on where the riders are coming from.

        Is Westlake’s demand due to the fact that it’s the (current) northernmost light rail transfer station in downtown? If so, it would mean that it serves as a good transfer station for other connecting routes (71, 72, 73, etc.) as well as regional routes. It would also mean that these transfers are also possible at University St station. Of course, we will find out when U-Link opens.

        On the other hand, what if the majority of Westlake’s demand was local (core area rather than regional)? In other words, do most of the riders go to/from the downtown area and its surroundings? If this is the case, then local mobility would be a deciding factor, and it would be less of an issue as long as they have access to quick transfers to regional networks. It would also be less of an issue if it is served by rail in the future (Ballard/West Seattle).

        In the grand scheme of things, as the system expands, it’s not necessary to serve every single station with every single line. At that point, it makes more sense to look at the function of the station and its accessibility to other lines. I’m just listing the possibilities and I am in no way making any conclusions here, but this is something worth looking into. If anyone has concrete data, I’d be interested to see it (not that I’d be influential in making any decisions…).

        Now, regarding the curve…There is a lot more to this curve than simply travel times, and they actually directly impact maintenance costs. Light rail vehicles are designed to take sharp curves, but it does so at a high cost, mainly due to the fact there is significantly more wear and tear on both the trains and the rails than there is for conventional rail. This means shorter maintenance/replacement intervals for the wheel sets and the rails, both expensive processes.

        It’s a fact that light rail track design has to contain higher tolerances than mainline track design, because light rail’s wheel designs simply don’t take disturbances (unevenness and curves) as well as traditional trains. The reasons are outlined here:

        Considering both the wear on the rails as well as the wear on hundreds of wheelsets, life-cycle/maintenance costs can increase significantly if these kind of curves are common in the network, and there are a few in our line.

        It may not be an issue in the short-term, but it would be a good idea for ST to see how much long-term maintenance costs they can save by eliminating these curves.

  4. From a rider’s perspective, it we build another tunnel, it would be most efficient to have one tunnel for northbound vehicles and the other tunnel for southbound vehicles. Build a center platform in the new tunnel and same-direction transfers would be almost seamless. The existing tunnel would require some retrofitting, but a center platform would be pretty easy to install. (It would also reduce by 50% the amount of wheel wear inflicted on the LRVs by the curves in the old tunnel.) But I don’t know if the operational objectives of building a new tunnel could be met with unidirectional tunnels.

    1. That would likely require some sort of grade separated junction at the ends where the two tunnels split again, but would increase both the frequency and the capacity by a lot. If you were waiting on one platform, you can take which ever train that shows up (providing you’re staying within Downtown).

      Cross-platform transfers can also be done with separate tunnels that serves both directions, except at one station (IDS or University). One of the tunnels would split and weave into the other one.

      This way you will have a station for same-direction transfer, while preserving opposite-direction transfers (because multiple lines may use the same tunnel, e.g. going from Bellevue to Rainier Valley).

  5. The main reason a second bus tunnel makes sense is because we don’t have unlimited money. To properly serve West Seattle by rail, you need at least three lines. That is ridiculously expensive, and won’t happen. This leaves us with a couple choices — either we spend a huge amount of money and build one light rail line and force everyone in West Seattle to transfer, or we improve the bus system. The latter would not only be a lot cheaper, but would provide better end to end service for the majority of West Seattle riders (because they wouldn’t have to transfer). As it turns out, this proposal would be just fine for West Seattle. Folks there could use the existing tunnel (it is well set up for it). But more improvements would be in order for West Seattle to provide an ideal system.

    Ballard is a little different. You can run a light rail line up to Ballard and it will work quite well for a lot of people in Ballard who are trying to get downtown (or get to some place along the way). Unlike West Seattle light rail, there are places (very populous places) along the way. The big problem is that buses from Ballard or Queen Anne (or South Lake Union or Belltown) wouldn’t use the bus tunnel. It is nowhere near their routes. As Al mentioned, the existing bus tunnel is designed to get buses from the freeways into the tunnel. But from the north and the east, this will go away. There will be no reason to run a bus down the express lanes and into a tunnel once Link gets to Northgate. Likewise for a bus from the East Side. Thus the existing tunnel becomes of rather limited value. It can serve buses quite well from the south (especially with some improvements made to surrounding freeways) but it adds nothing of value to buses coming from the north.

    This means, for example, that unlike the WSTT, it can’t serve buses from Aurora. Nor can it serve buses from Ballard or Belltown. This means that you are completely dependent on us building more light rail to those areas. So, after spending a substantial amount of money on a new tunnel, you have to follow it up with a substantial amount of money on new light rail. If Sound Transit remains determined to build light rail from Ballard to downtown first, then such a plan is reasonable. Build a new tunnel so that all trains can run in the new tunnel, and use the old tunnel for buses. But that still would do nothing for those along the Aurora corridor. That is a lot of money for something that can be built later. I would hate to see more important projects (like UW to Ballard light rail) be but on the back burner, while we build a new Ballard to downtown line. In other words, this sounds a lot more like an implementation plan for a Ballard to downtown light rail line. If it is built, and goes as far as SoDo, then this is one way to do it.

    But I don’t see it as being a very good value. The best part about a WSTT is that it isn’t that expensive and provides major improvements to various neighborhoods. As mentioned, it is part of an ideal (or at least realistically ideal) system to West Seattle. I don’t think we will ever have the money to build an ideal light rail system to West Seattle (like I said, three lines) but we could build a top notch bus network there. A new tunnel would be part of that. This is far less expensive than Ballard to downtown light rail, let alone West Seattle light rail. At the same time, you would be providing substantially improved service to Ballard, and completely grade separated service to Lower Queen Anne, Belltown and South Lake Union. Those on the Aurora corridor would also see service that is realistically as good as it could ever get. I think a rail line on Aurora is just not going to happen — but really good bus service (traveling in HOV lanes on Aurora and then in a tunnel at South Lake Union) would be a huge improvement.

    So again, I think this is just another way that Ballard to downtown light rail could be implemented. But as has been mentioned many times before, Ballard to downtown light rail is not the best value. It should not be a high priority. There are many things we should do first, such as:

    1) Ballard to UW light rail
    2) A “Metro 8” light rail line
    3) Bus improvements for West Seattle, Queen Anne, the Aurora Corridor and Ballard (which include, but are not limited to a new tunnel) .

    The best part of the WSTT is not that it could eventually be converted to light rail, but that it could (with other improvements) provide really good bus service to lots of areas. You would have grade separation from West Seattle to Queen Anne, South Lake Union and Aurora, while providing really fast service to Ballard. I just don’t see how you can build a better transit system for less money than those three projects right there. I could easily see how we could blow a lot of money on other projects, and fail to get anything nearly as good.

    1. Fifty years from now, I would envision the Puget Sound light rail system like this:

      1) Airport > Rainier Valley > Downtown > Ballard > (University District). The Ballard extension would be designed and engineered just like the existing Link line (a relatively low speed line with many stations and some street running).

      2) North Link > Downtown > West Seattle > Airport > South King County/Tacoma. This line would be designed and engineered for higher speed operations than the existing Link line. Fewer curves, less street running and different vehicles would permit faster trip times between downtown and the airport. Trip times from south King County and Snohomish County would also be faster than bus service.

      3) East Link > Downtown. This line would be another high speed line, but it would likely terminate in downtown unless it is extended to the U District.

      1. That would be way more expensive and improve transit a lot less than the three proposals I mentioned. With the three proposals I mentioned, transit mobility is changed dramatically — for the bulk of the city, riding transit is faster than driving. Bus to rail connections are made much better as well.

        Light rail, in any way shape or form, will never operate as fast as an HOV3 running bus from Tacoma to Seattle. It won’t run as fast as an HOV2 running bus most of the time. This is nothing new. A 41, for example, is faster from Northgate to Westlake than Link will be (at least it is faster in the morning). But the trade-off are very high level attractions like the UW and Capitol Hill along the way. That doesn’t exist for most of the south end. There just aren’t that many people wanting to get from, say, Tacoma to Delridge in West Seattle. Neither are there many people in West Seattle who want to get to a station between West Seattle and SoDo — because there won’t be one. In other words, none of the lines you mention would be a huge improvement over what is possible with buses. The same can not be said for the two light rail lines I mentioned (UW to Ballard and Metro 8 Subway). Even when you run a system with very few stops, running very fast, you still don’t get huge numbers of people from far away to ride it. BART is very fast from Fremont California (a city the size of Tacoma) to the Bay Area (an area much bigger than Seattle) but it only carries as many people as a typical Seattle bus. The big numbers are East Bay (Oakland and Berkeley) to San Fransisco. It isn’t even close.

        Which is not to say that your ideas lack merit. A second southern line could make sense. You could send the Rainier Valley part out to Renton, and build a fairly cheap bypass (from SeaTac to SoDo busway). This would provide the kind of fast, commuter rail type system that folks in the southern suburbs likely prefer. My guess is that like West Seattle, there aren’t huge numbers of people trying to get from Federal Way (or Tacoma) to Rainier Valley. They could deal with the current line running a little less frequently (I would keep all the lines, just run the other two more often)..

      2. This is where design-to-objective comes into play. What would it take to build a line from south King County > Airport > West Seattle > Downtown that would be faster than a bus in the HOV lane and still be operationally efficient in the year 2050?

      1. That doesn’t add much, though, for folks on the north end. Traffic is horrible from Westlake to Mercer (no matter which direction you go) and I can’t see any bus connecting at the Convention Place Center once Link gets to Northgate.

        If the area in green (or at least the area in green north of Westlake) is connected to the existing bus tunnel, then it would be fine. I explore that idea in the next comment. Basically, it would mean (at the very least) extending the existing tunnel so that it matches the new WSTT. That would be more expensive, but would offer up the chief advantage you mentioned (smoothing out the curves) as well as perhaps a new station at First Hill. Connecting at University, instead of Westlake is a reasonable trade-off for the latter, certainly (I would take it). Whether it is worth the money or not is hard to say (especially since you could add a bus tunnel station at Madison on First Hill with a new bus tunnel as well). So basically it still gets down to whether it is worth spending a bunch of money to smooth out the curves. I have a feeling it isn’t.

    2. OK, reading some more (especially Shane’s comment above) I realize that there is another possibility here. Essentially, this could become a way to implement the WSTT. The key elements of the WSTT are:

      1) Entrances at the SoDo busway, Aurora and South Lake Union, along with a stop at Belltown (

      2) A new stop at Madison. The plans suggest a stop at fourth (to save money) but if we could afford it, this stop could be moved up the street (providing a First Hill stop).

      The existing tunnel could be retrofitted to provide the entrances (it already has a SoDo busway entrance). A new station could be added at Madison for the new train tunnel. I’ll deal with each idea separately.

      Retrofitting the existing tunnel to be more like the WSTT would not be that much different than building a new tunnel. Either way you have to build a tunnel north of Westlake and a tunnel paralleling the old tunnel south of there. But by my estimation, this approach would still require extra tunneling. You would basically be throwing away part of the existing connection between Westlake and the Capitol Hill station. You could keep that piece, but as mentioned, it really isn’t valuable in a few years. From what I can tell, the additional cost would be for the new connector — basically removing the tight radius curves. I think That is a trade-off. Basically, it would mean spending a fair amount of money to deliver better operation efficiencies. You could, of course, do that today (without building a new tunnel). I’m not sure it is worth it, unless you added a new station (on First Hill perhaps).

      As far as stations go, one of the reasons that the WSTT can add a station at Madison is that it connects to both the north and south end of the other tunnel. Someone coming from either end of the system could switch to a (very frequent) bus to save a few blocks of walking. This would be more likely the more the line moved up the hill.

      With the new tunnel, it wouldn’t make sense to add a stop at both Madison and University. So basically, you would replace the stop at University with a stop at Madison, perhaps up the hill. This would be more expensive (require more tunneling) but it would provide for a much needed stop (or two) on First Hill. So, essentially the new light rail would diverge from the Pioneer Square station, and then add a stop (or two) before Capitol Hill Station. To see what I’m suggesting, look at this crude sketch: The squares are existing stations. The circles are new WSTT stations and the stars would be new light rail stations.

      One drawback (other than the added cost) is that this would lead to a lot more transfers. Folks coming from Capitol Hill or the UW would have to transfer to get to the north end of downtown. Someone taking a bus from Ballard, Queen Anne or Belltown would go all the way to Pioneer Square, then head back northeast to First Hill and Capitol Hill. Despite this drawback, I don’t think this is a crazy idea. You would get a couple First Hill stops. The distances here are fairly short, and if we built a Metro 8 subway line and the UW to Ballard light rail, the system would be fairly efficient. I’m just not sure if folks would embrace transferring (especially transferring to a bus) once on a train.

      You could split the difference, of course. You could add a station on First Hill, but keep the routes almost exactly as you had it. But you could do exactly the same thing with a new WSTT — on Madison no less. It wouldn’t have the operational efficiencies as your proposal, but it would still provide a much needed station.

      1. Ross, I really do like what you’ve sketched out here. It allows us to go back and fix some of our most egregious errors (improperly serving Capitol/First Hill, building a rail-bus tunnel that doesn’t work well at all for rail (see the Westlake curve, the IDS portal, the slight curves at the ends of the platforms)) while moving ahead with the sensible WSTT idea. I think it might be a tough sell but on the surface I think it’s worth it.

  6. I completely agree that buses from the west will need access to the tunnels.

    I went through Sound Transit’s report that contains support for a second tunnel.

    Basically the emphasis was on the fact that most of the reliability issues will be the result of exceeding surface capacity by 2035. It also says that “In addition to serving Ballard and West Seattle/Burien/Renton-bound riders, a tunnel or tunnels accommodating both rail and bus vehicles would serve multiple travel markets, reliably accommodating most unmet demand from surface-routed corridors. I don’t really know what they mean by “reliably accommodating most unmet demand” because we’re seeing that DSTT isn’t reliable at all.

    But now I’m wondering if it would be possible to build additional access points into the existing DSTT just north of University St station (provided rail is shifted to the new tunnel). That would solve the access problem for West-side buses. This would have to be done anyway if the new tunnel was built for buses.

    Also, a rail-only tunnel wouldn’t necessarily be more expensive than a bus-only tunnel. In fact, it may be less expensive to design it for just one mode rather than two (also see my point in the article about maintaining unused rail equipment for a dual-mode tunnel).

    1. I agree, building for one mode is cheaper. I think if there is additional cost it is because you might have to do more digging. This is the way I figure it:

      If you build the WSTT as sketched out here ( there are really a couple of parts:

      1) A tunnel north of Westlake.
      2) A tunnel south of Westlake.

      If you reuse the existing tunnel, then you still have to build:

      1) A tunnel north of Westlake.
      2) A new tunnel south of Westlake, but one that is a train tunnel, from the south end to University Station and then connecting to the Capitol Hill station.

      So basically it is comparison of the two southern tunnels. In other words, if you are digging a tunnel from the south, once you get to University, you can either keep going (to Westlake) or curve over to rejoin the other tunnel. It isn’t clear where it would rejoin, but it looks to be around the freeway. I think that is bound to be a little more expensive. Maybe it is worth it to straighten out the curves. It would certainly be worth it if a First Hill station could be built. But as I said, you could add a First Hill station — a better First Hill station in my opinion — by moving the Madison WSTT station up the hill. If you look at the WSTT diagram and imagine the Madison Street station moved up to, say Boren, you have a really nice looking system. The second tunnel is less redundant and you still have a one stop connection to either end of downtown.

      As far as building for both modes are concerned, I think there is no avoiding it, unless you want to commit to building light rail to Ballard right now. The green section on your map is critical. Without it, the bus tunnel is of little value for those to the northwest (and South Lake Union). You either dig farther, or all you are doing is building a nice system for West Seattle. That’s good, and still a better value than building light rail to West Seattle, but not great. It means South Lake Union, Queen Anne and the Aurora corridor have essentially no improvement. Ballard could be OK with UW to Ballard light rail, but the other areas are left out for now. If anything, I would prefer building a bus tunnel and let it go at that (assume it would never be converted for rail). If there ever is a line, it will be out to Ballard, and as mentioned, that isn’t as big a deal if UW to Ballard rail is built.

      But I don’t think we have to be so negative about shared operations. This is being sold as a dual use tunnel, and it should be engineered for dual use. The existing tunnel was never engineered for that. They basically built a bus tunnel and thought that someday light rail might replace the buses. But I don’t think anyone figured we would run both buses and trains through the tunnel at the same time for twenty years. That is part of the reason we have so many problems. Folks are aware of them, but know that they are going away soon, so no one bothers to address them.

      Then there is a the headway issue. With these improvements, what is the headway of trains through the “core” (University to I. D.)? The plan is to have trains running from the UW to downtown every four minutes, but it is capable of three (eventually). So unless you get headways down to 90 seconds, you are reducing the capability of the system. Two minutes might be OK (meaning four minute frequency from the other lines) but any more than that and you hamper the most important section (UW to downtown).

      If we build a new WSTT, I’m definitely open to building a rail only line (with the improvements you mention) and then moving the buses over to the existing tunnel. But I think a tunnel used by buses must include the green section, and will therefore be engineered for dual use. I also think that losing the direct connection between Capitol Hill and Westlake is unfortunate, and the new curve might not be worth it (especially if it costs more). It would give us a chance to add a First Hill station, though, and that changes the equation considerably. To me, there are three good choices:

      1) The WSTT as described here:
      2) That same WSTT, but with the Madison station moved up the hill. This is more expensive, but might be worth it.
      3) Make the changes you suggest, but make the green part of this map ( part of the bus tunnel, and add a new station on First Hill (since you have to dig to straighten out the curve anyway). I think this would be the most expensive option (initially) but the operational improvements (and the First Hill station) might make it worth it.

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