When we talk about building West Seattle or Ballard service, there’s often an assumption that this service could use the Downtown Seattle Transit Tunnel we have now. As far as I’m aware, it can’t.

The light rail spine we’re building now will eventually go through Federal Way to Tacoma, and through Lynnwood to Everett. The tunnel will be used not only for trains that run straight through from Everett to Tacoma, but also for trains that run from Everett (or at least somewhere north of downtown Seattle) to Bellevue and Redmond.

We’re starting with service on Central Link every six minutes during peak times. It’s probably reasonable to consider service down to headways (time between trains) of two minutes – the closest headways I’ve seen in any Sound Transit documentation are 2.4 minute, from their 2005 long range plan.

After University Link opens, I sincerely hope we’ll be looking at lowering headways during peak times. Maybe this will be to five minutes. If we build Sound Transit 2 just to Northgate and Bellevue, we’re going to add trains to the tunnel to bring headways down further. We’d have trains to the Rainier Valley every five minutes, and then trains to Bellevue every 10 minutes. The easy way to figure out combined headway is to figure out how many trains that is per hour – 6 for Bellevue, 12 for the Valley – and then divide the number of minutes (60 in an hour) by the number of trains (18). Let’s round this to 3 minutes.

This is a hundred year plus system – it’ll still be operating after all of us are long dead. We’re certainly going to increase the frequency of the trains on this line in the future – maybe even soon. We need the flexibility to do that.

Ten years ago, the monorail project was talking about 3 minute peak headways for Ballard-West Seattle. Combine that with just the potential ST2 service, and you’re talking about 1.5 minute peak headways. Those are physically possible, but that’s it, then. We wouldn’t have any room for ST3, no room for ST4, nothing.

New rail through downtown will need new right of way.

50 Replies to “The DSTT Will Be Full.”

  1. Why does no one discuss the buses in the transit tunnel? What is going to happen regarding them, and will trains ever have to wait on buses?

  2. Both the ST2 proposal and the current East link proposals reference connecting to the Central Link at the ID station.

    But there are no references to actually passing thru the entire DSTT.

    It’s possible that’s not part of the plan.

    Another possibility would be for the vehicles to change in the tunnel. Example: a University Line vehicle continues thru the tunnel, then becomes an East Link vehicle. This would cut traffic substantially in the tunnel, and the nearby Central base could act as the feeder to add/subtract vehicles to maintain headways, etc.

    A new tunnel is a non-starter.

    Also, it’s possible the East Link would terminate at street level at the ID station on 5th Ave. The recent re-routing of the I-90 ST buses to 5th Ave from 4th Ave would support that. I never understood why they added that jog into the route at Washington.

  3. Brad:

    There are LOTS of references to East Link trains going through the DSTT. That’s the big ridership benefit for East Link on 90 as opposed to 520 – you get a one-seat ride from Northgate to Bellevue on 90 because of interlining.

    That has always been the case. Have a look at the fact sheet:

    New ROW through downtown will be absolutely necessary for a new line to Ballard or West Seattle.

  4. rizzuhjj, I’ve addressed that issue in comments before, but just never posted about it.

    1) Buses and trains will be separated in the DSTT with the new signaling system for the first few years of operation. The proposed travel times account for some bus delay. Don’t freak out.

    2) Buses will be kicked out of the DSTT as train frequencies increase.

  5. We will need a second tunnel at some point no matter what we do.

    Engineering it could be very challenging: there’s already the BNSF tunnel, the DSTT and the waterfront. Downtown at that narrow point is only a few blocks wide.

    Second Ave would be the best place, since it would be a short walk to the DSTT on third, but it’ll be a challenge with the BNSF track underneath.

  6. use the TBMs to dig under 1st ave from the INTL district station towards Interbay

  7. gordon, a two block walk to transfer between Link and a new system would be prohibitive, given the hill. 2nd Avenue is probably a better choice – one could build cut and cover direct transfers under some of the cross-streets.

  8. michael, in terms of people getting access to transit, walking one block from 1st is fine.

    In terms of closing the street where all the action is for a couple of years for construction, that’s ANOTHER good reason to do construction on 2nd.

  9. Ben, thanks for the information. Where can I find documentation backing up that buses will eventually be phased out of the tunnel.

    Apologies if I sounded like I was freaking out. :) It just seems like something that isn’t discussed.

    It is not going to be fun sitting in a train waiting for some buses to clear out, that’s for sure. That will be a very obvious criticism of ST1 in the beginning.

  10. And I really have to say the talk about a 2nd avenue subway is interesting but perhaps a bit too premature. Even as an avid ST supporter I seriously doubt we’ll be voting on anything relating to that before 2016 at the very earliest.

    When do ST1 taxes sunset? Pretty much at the end of ST2 if ST2 passes, right? Yeah, I can’t imagine we’d increase about .9% for ST (as well as .9% for KC Metro).

    What do you think, Ben?

  11. I like the idea of a 2nd Avenue tunnel. You got a streetcar on 1st Avenue, a light-rail line on 2nd Avenue, and a couple more light-rail lines under 3rd Avenue. That’s amazing!

  12. sorry, but i think a second ave. tunnel would be a terrible idea. its just a bit too far for people to be willing to walk. The best thing would be another tunnel underneath the dstt. In most other transit systems in the world, you’ll see plenty of stations that have different levels for different lines. That makes a seamless transfer, which is very important.

  13. Jonlin, one block in Seattle is a pretty short walk. People walk just half a block or more to transfer buses anyway depending on where you are going.
    Have you been to Paris at all? I think in the Chatelet station because of all the lines that intersect there, some transfers I swear felt like I was walking or on a moving walkway for maybe 1/2 a mile. Factoring in all of the up and down and around when walking or transferring lines and one definitly walks more than a “Seattle” city block inbetween transfers.

  14. Jonlin, I don’t think you’re accurately gauging these distances. Not all blocks in Seattle are created equal – the distance between 2nd and 3rd Avenue in downtown is tiny.

    The Benaroya exit from the tunnel is closer to 2nd than it is to 3rd, even. Many users walk a lot longer than that just to get to their bus AFTER they’ve entered the tunnel.

    rizzuhjj, go to the Sound Transit project pages for the tunnel stations, and email the public outreach rep (or call them) for backup on the buses eventually being kicked out. I really don’t think anyone’s going to have problems with the status quo, anyway. We have only low-floor vehicles with flip-out wheelchair ramps in the tunnel, and there haven’t been operations problems that would suggest we’re going to have any trouble with rail.

    I’m not that interested in talking about ST3 or later either. I’m just pointing out that the DSTT should be left out of people’s ideas for the next phase.

  15. “…a two block walk to transfer between Link and a new system would be prohibitive, given the hill.”

    You do much more walking than that in London. Some of the standard connections are a long way apart. You get to hike with a crowd.

    The hill issue could be taken care of with underground escalators.

    The need for more downtown transit capacity (grade seperated) should be looked at along with the viaduct replacement. The two could be combined.

  16. Phil, they cannot be combined, mostly because of how the 2005 Transportation Partnership Package was written.

    And there are plenty of other reasons 1st Avenue is a non-starter. It’s a much busier street to tear up, it would affect significantly more historic structures, and there really IS a major difference in ridership caused by the longer transfer. Just because you can do two different things doesn’t mean they don’t have two different impacts. It would also require much greater downtown expenditure for underground work. One block is half as expensive as two blocks…

  17. Just in general, when bringing up cities like London and Paris – they wouldn’t balk for a second at a subway extension or a new line. They have different standards for making decisions about transit. There are connections in Tokyo that are a three or four block walk through underground mazes – but they’d be a political nightmare here.

    There will be no new downtown transit right of way – aside from perhaps more streetcar – for a good ten years. ST2 needs to pass first, and then after that, we still need to get to Mountlake Terrace. At that point, we actually have money to spend, with North King!

  18. use the TBMs … then you don’t have to worry about cut and cover construction.

    and boo hoo if there is construction for a couple of years … we’d get grade-separated transit out of it so in the end we’d be better off

  19. it shouldn’t be that difficult to connect the Westlake Mezannine Level to a station on First or Second Ave … it could also connect that pit that they have on 2nd and Pike/Pine.

    if the line is underground, it can also bend towards Westlake so that it would serve both 1st and 2nd.

    My thinking about 1st ave was that is where the attractions are … close to the ferry, pike place market, etc … and then head N. to Interbay (could pop out of the ground where Denny/Westlake/Elliot all meet up (north of the sculpture park)

    it could also manage to go over the BNFS tunnel and head towards West Seattle …

  20. Regardless …

    lets get AIRPORT-UW done.

    then we can concentrate on the


  21. Ben,

    Buses use the viaduct now, and making sure there are seperate lanes is not outside of the scope of the replacement. No reason those lanes can’t be used for future light rail or trolley if planned for correctly (grade, strength). I’m wasn’t talking about digging up 1st Ave, so not sure what you meant.

    “…cities like London and Paris – they wouldn’t balk for a second at a subway extension or a new line.”

    Yeah, right…like they don’t have knock-down, drag-out fights over there. I remember the fighting over the Docklands Light Railway; waste of money, no one lives there, toy train, etc…Sound familiar?

  22. gordon, a connection to 1st avenue would be a three block walk from Westlake – the Westlake station is between 4th and 5th. That’s not doable.

    The line can’t really “bend”. It has to follow the existing streets, and any deviation requires extra boring and a lot of depth, or demolition of an existing surface structure, both of which add a HUGE expenditure.

    Redmond-Bellevue-UW? You mean 520? Are we seriously having this discussion again? Not happening, not for 40 years.

    Phil, at this point, then, I have no idea what you’re talking about. Something about the viaduct, but also about 1st Avenue?

  23. They have an exit from the Westlake station almost on the corner of third and Pine, that’s like 400 feet from first ave.

    15,000 people already walk between 3rd and 2nd ave on pine.

  24. sure, quite a few people would walk from second to first. but those are mostly people who would be taking transit anyways; a one-block connection is enough of a hassle that people who are considering transit with instead drive their cars. london, paris, new york, tokyo; all those cities are built on transit, and it is completely impractical not to take it. unfortunately, thats not the case here, and its pretty hard to get people to take any transit at all.

  25. sorry, thats second to third. and remember the monorail? part of the reason it was killed is because it would be too hard to get from second to third. and also, what is the advantage of having it on second? third is in the middle of everything, allowing for the most people to have the shortest walk to their destinations downtown.

  26. You know guys, it’s not like if there’s a second ave tunnel that the entrance to the stations will be in the middle of second avenue.

  27. It’s a good idea, rizzuhjj, I wonder if it’s feasible technologically. In San Francisco, they renovated the Market Street subway to hold Bart over Muni, maybe it can be done here.

  28. Ben … East Links is supposed to go across I90 to Bellevue and then towards Redmond. I said nothing about 520.

    If sound Transit is any good, then they will plan it so that there is a line from the east side to UW and to the Airport

  29. as for underground mezzanine levels.

    look at NYC … there are tons of examples where there are multiblock underground passages.

    In addition to connecting between lines it adds available retail space, respite from the rain and a way to avoid traffic.

    It is not impossible to do and Subway lines DO bend all the time between avenues and streets… again look at NYC.

    Would it be easy? no. but it wouldn’t be impossible

  30. So, before everyone panics over the prospect of the DSTT being full, it might be useful to reflect on what this implies.

    At 2.4 minute headways (25 trains per hour per direction) using 4 car trains with 800 passengers per train, this represents 20,000 pphpd. – or 400,000 ppdpd assuming the current 20 hour service day. Both directions would represent 800,000 passengers per day.

    These are huge numbers, and if this ever happens we should congratulate ourselves and ST for a job well done – we will have just about the most successful LR line in the world.

    Assuming it does happen some day, then what??

    Well, for starters we would probably investigate improved operations and control. Just reducing the 2.4 minute headways to 2 minute headways would increase capacity an additional 20%, and at much less cost than a new line.

    After that we would look to building a new N-S line. It would go underground under 2nd Ave with an underground connection to the first line at least at University. Compared to a 1st Ave line, a 2nd Ave has better integration with the first line, higher ridership, and undoubtedly easier construction (lower water table, additional clearance over the BNSF tunnel, etc).

    As far as the comments about 1 block being too far to transfer between lines – give me a break. Going from 2nd to 3rd in Seattle is going the short distance on our DT blocks, and the distance is actually substantially shorter than length of the 4 car Link train that the transferring passenger supposedly rode to get there.

    A one block transfer in DT Seattle is not a prohibitively long distance – in fact, while riding some European systems I can swear I’ve walked much farther just looking for a restroom, or maybe it just seemed that way……In any case, it’s not a big deal.

  31. Another way to increase through-put is to lengthen the platforms and run longer trains.

    Remember, the Big Dig became a financial nightmare because they were criss-crossing layers while maintaining service. It was a tremendous engineering and construction accomplishment, and also stands as a lighthouse on a financial reef, flashing a warning to future engineers.

  32. lazarus, thank you. Indeed, 2nd to 3rd is just fine.

    We’ll likely tunnel under 2nd avenue for a second line.

    Seriously, one over the other? The current line already drops under the BNSF tunnel twice. You’re talking about going under the water line. Totally unfeasible, sorry.

  33. There are some major problems that some of you have forgotten.

    The BNSF tunnel runs under 2nd Ave for a good part of it’s trip. That is why the Discovery group wanted to have a Sounder connection to the DSTT.. It would be VERY close. In fact, if a train is working hard enough, you CAN hear it (BNSF) at the University Street Station.

    I do see the logic however in having the 1st Avenue Streetcar, 2nd Avenue Ballard/Westlake Tunnel, 3rd Ave U-Link/Airport/Eastside Tunnel…that’ll be very European and would be excellent…

    And in this case, a TBM would not be recommended for this. Cut and Cover takes a lot less time than launching a TBM. Remember, it has to be launched twice unless they got 2 of them but it would still take years to the corridor.

    Take a lot at the Skytrain “Canada Line” construction.


    Construction started on that line in Fall 2005 and is slated to open in November 2009. The 19km (11.8 mile) $1.3 billion dollar line is mostly cut and cover, elevated, bridges, etc. Basically everything that Ballard/West Seattle could be is being built now.

    On a side note – There are A LOT of new light-rail and commuter rail openings in 2009!

  34. Ben,

    For clarification: I believe your last paragraph refers to building the supposed new LR line under and parallel to the current DSTT. I concur, it wouldn’t be worth the added time, cost and disruption – it’s just not worth the effort.

    Parallel on 2nd but tied together at stations is a better bet. Even in Europe where it sometimes seems like multiple lines are stacked underground, they are usually offset or crossing.

  35. Brian,

    Although I must admit that it is hard to find good maps showing exactly where the BNSF tunnel is relative to the DT Seattle street grid, my impression was that the tunnel does not follow 2nd (if it follows the street grid at all).

    I base this assumption on the following:

    First, at KS Station the tunnel entrance and 2nd ave have already departed, with the tunnel entrance being at something like a 30 deg angle to 2nd ave.

    Second, the DSTT crosses the BNSF line twice. Since the DSTT is on 3rd, this implies that the BNSF tunnel must somehow be to the East of 3rd for part of its route.

    Third, historylink.org puts the meet-up between the north tunneling crew and the south tunneling crew as having occurred under 4th and University. This might be why you can hear trains in the BNSF tunnel while being in the DSTT at University.

  36. Brian, I agree – cut and cover will be the way to go, like most of the 3rd Avenue construction.

    I was under the impression, that the BNSF tunnel took a pretty diagonal route under the city. I have a downtown Seattle map from Kroll that I thought showed only one crossing of 2nd, and I’ve been basing my assumptions on that, as they use pretty good GIS data.

    You can see the south portal connects to 4th – the DSTT goes under it there. I thought the DSTT dropped under the BNSF again between University and Westlake – which is why you can hear the trains there.

  37. The DSTT was primarily bored – using methods not to much different than what ST just used for the BH Tunnel. Cut and cover was used only for stations and for the segment from Westlake Station to Convention Place Station.

    I suspect a 2nd Ave LR line would be built the same way – bored except for stations and maybe the BNSF tunnel crossing (if required).

  38. Thanks, Lazarus. I think you’re right, then. It’ll be a lot like Canada Line construction (where the stretch between stations was bored).

  39. Ben, you sure that stacking the two lines would put it under the water line? I don’t know much about water tables, but the elevation of 3rd ave is pretty high. Besides, how is it possible to have two stacked lines in SF at sea level with the planned expansion of the 3rd street light rail to the north passing under both of those?

  40. sorry, didn’t finish my question…
    How is it possible to have two stacked lines in SF at sea level with the planned expansion of the 3rd street light rail to the north passing under both of those while it is impossible to stack 2 lines ~100′ (?) above sea level?

  41. I have not left the best comments on this thread. :)

    Wesley, the DSTT drops under BNSF, as far as I know. Another line below it would almost definitely go below the water line. Under the water line would be possible, but much more expensive. SF has a big tax base to pay for projects like that. We don’t. It really wouldn’t offer us any benefit over going under 2nd, though, and any transfer benefit would be negated by losing riders from 1st who would walk 1 block, but not 2.

    SCO, lengthening platforms in the DSTT would be prohibitively expensive and likely close the line for some time. That’s really deep construction, and you’d have to replace bored sections with cut and cover in place… I think we’ll get a third system engineered for very high capacity before someone did something like that.

    Remember that Paris has some 70m platforms. They’re not extending old systems, they’re just building new ones.

  42. Well, I was wrong!

    Here is from the Benaroya Hall website

    “The facility sits directly above the BNSF Railway tunnel under Downtown Seattle that is the primary rail corridor for the city and adjacent to the Metro Bus Tunnel . To isolate the performance hall from the rumbles of the traffic in these tunnels and the streets outside the hall floats on rubber pads to isolate it from the outer shell of the building. These same noise-isolation features also dampen the sensation of earthquakes within the facility.”

  43. but that would mean a new tunnel would have to go below the bnsf which is below the dstt, right? I guess it would still be better to have it at 2nd. I kinda like the idea of having escalators that would connect the two stations. Maybe they could make them quick to access from the street to facilitate lugging my lazy ass up the hill.

  44. Wesley, the DSTT drops under the BNSF, not the other way around.

    A 2nd Avenue tunnel would be just like building the DSTT.

  45. Or you could force a transfer at Westlake between LRT lines – Thus you’d build a new tunnel thru Denny Triangle (Clise Properties)/ Seattle Center/QA which pops out onto 15th Ave W to Ballard. The light rail would terminate at Westlake, forcing a transfer to the DSTT. (Another intriguing option – considering this is years out – is the removal of the Monorail and a cut and cover tunnel under 5th Ave).

    The Ballard extension with a transfer at Westlake is more reasonable than thinking about a second transit tunnel thru the downtown core to satisfy West Seattle. West Seattle will never get LINK – it’s just not dense enough.

  46. Hey anonymous,

    If we built to Ballard, we’d probably want to complete a downtown tunnel so that there was a one seat ride from Ballard to all the major points downtown. You’d get really low ridership if people had to transfer to get to the Wells Fargo building, or the Columbia Center – some of the major downtown office towers are significantly south of Westlake.

    Also, King Street Station is significantly south of Westlake. Sounder users who’d want to use this line to get to work would have to transfer twice (assuming they didn’t transfer to get on Sounder!), and Amtrak and Sounder service are steadily increasing, so this wouldn’t reduce cross-downtown bus needs.

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