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When discussion of potential future light rail lines comes up often cost effectiveness is a topic of debate. I decided to run the numbers using Sound Transit’s numbers from their corridor studies.

Methodology I took the high cost number from each light rail alternative and divided by the low end of the average weekday boardings to give a cost per average weekday boarding. Costs were rounded to the nearest 100 million. The final cost per average weekday boarding was rounded to the nearest thousand.


  • It may not be valid to compare costs and ridership between corridor studies. At the level of detail in these studies the numbers are likely intended only to compare alternatives within the corridor.
  • It appears with the exception of the Everett and Tacoma Central Link extensions ridership estimates don’t include adjoining corridors. In particular Ballard-Downtown likely loses a lot of ridership by not including the downtown tunnel serving IDS/King Street that is in the West Seattle study.
  • I did not include the light rail alternatives from the ERC study. The ridership numbers were very low even compared to alternatives in other Eastside studies that use the ERC between Bellevue, South Kirkland, and Totem Lake.
  • I did not include the Angle Lake-Federal Way or Overlake-Redmond corridors. These are almost certain to be in ST3. I also did not want to go find the cost and ridership numbers or convert the costs to 2014 dollars.
  • I did not include past HCT studies such as the 522 corridor study. I’m not sure if these would be on the table for ST3 and I didn’t want to dig for the documents or convert costs to 2014 dollars.
  • Alternative B4 in the South King studies is two separate rail lines. One to White Center via a tunnel under Alaska Junction. The second one to Burien and Renton via Georgetown, South Park, and SR 509. Since Sound Transit broke out costs and ridership separately I did so as well. I also re-ran the numbers for Burien-Renton with an extra billion for a Downtown Seattle tunnel. The Sound Transit numbers didn’t include this cost in the costs for the branch and it is unlikely this would be built as a stand-alone line without the tunnel.
Alternative Description Cost per boarding
A Paine Field 92,000
A with option Paine Field + ECC extension 95,000
B I-5 69,000
C SR 99 86,000
Alternative Description Cost per boarding
B2b U District to Totem Lake 414,000
C2 U District to Redmond via East Link 144,000
C2a U District to Bellevue 289,000
Alternative Description Cost per boarding
C1 via Richards Road 300,000
C3 via I-405 289,000
A1a with Issaquah Highlands extension 300,000
Alternative Description Cost per boarding
A3 via Wallingford tunnel 86,000
B2 via Fremont 86,000
B2 with option via Fremont with elevated segments 76,000
C1 via Fremont and Wallingford 74,000
Alternative Description Cost per boarding
A Interbay, Ship Canal tunnel 150,000
A with option Interbay, Ship Canal bridge 133,000
B 15th Avenue elevated 127,000
B with extension 15th Avenue elevated + 85th extension 111,000
C 15th Avenue streetcar 86,000
C with extension 15th Avenue streetcar + 85th extension 78,000
D Queen Anne tunnel 138,000
E Westlake streetcar, Ship Canal tunnel 86,000
E with option Westlake streetcar, Ship Canal bridge 57,000
E with extension Westlake streetcar, Ship Canal tunnel + 85th extension 81,000
E with option + extension Westlake streetcar, Ship Canal bridge + 85th extension 56,000
Alternative Description Cost per boarding
A3 Delridge 97,000
A5 via tunnel to White Center 126,000
B4 West Seattle tunnel, second line to Burien-Renton via 509 106,000
B4 Downtown-White Center to White Center via Alaska Junction tunnel 167,000
B4 Downtown-Renton via 509 to Burien-Renton 65,000
B4 Downtown-Renton via 509 to Burien-Renton with Downtown Seattle tunnel 85,000
C5 elevated to White Center 141,000
Alternative Description Cost per boarding
1 SR 99 West 92,000
2 SR 99 Center 121,000
3 SR 99 Hybrid 108,000
4 SR 99 to I-5 109,000
5 I-5 West 88,000
6 I-5 East 79,000

14 Replies to “Cost Effectiveness of Potential ST3 Rail Alignments”

  1. Chris,
    Thanks – this is good info for numbers-minded folks like me. If you get a chance to edit, a link or two to your primary sources would be much appreciated.

  2. At what point are these ridership numbers taken? 20 years in the future? Immediately after opening?

    A more expensive line per rider at initial cost may be worthwhile if it attracts long term development patterns that ultimately increase ridership.

    I-5 alignments will be fast, but there are only certain types of development that are willing to be next to a wide, loud freeway.

  3. It’s a shame that the studied routes suck.

    I wonder what the cost per rider numbers would be for some of Seattle Subway’s proposed alternatives.

    Anybody know how to calculate ridership, cost, or cost effectiveness.

    1. Also remember these studies are at a conceptual level. Ridership estimates and costs are likely to change.

      A big difference will be using more realistic population numbers. I believe Ballard and Fremont both have more people and employment than the PSRC model is estimating for 2040.

      Another difference is extending the Ballard-Downtown line to IDS. Apparently that causes a big ridership hit in the level of modeling used at this stage.

    2. Finally cost-effectiveness is not the be-all and end all. Other considerations like TOD should influence the final decision.

      The Queen Anne tunnel was by far the most popular alternative in the public hearings for the Ballard-downtown study. There is a case to be made that the public will support “go big or go home” alignments that aren’t the most cost-effective.

      The larger lesson here is the extensions to Everett and Tacoma don’t have as horrible an ROI as some would like to believe. Similarly West Seattle/Burien-Renton don’t look so bad on an ROI basis. Especially compared to other corridors.

  4. I’m sure that it’s clear to all of us, but it would be a good idea to emphasize that these figures are not “per rider”, they are “per average weekday daily rider”.

    It would be good to extrapolate a “per ride” cost assuming 30 years of operation and 250 working days per year. That would give a reasonable value of the capital cost per commute ride taken, and it would be much less of a shock to the casual reader though still rather large.

    1. Good point on the costs being per average weekday boarding.

      I probably won’t turn this into an actual cost per ride. I simply wanted a metric for comparing the various alternatives in the various studies ST has recently released.

      To that end a few things surprised me:
      1. I knew Lynnwood-Everett was a pretty good line (in spite of the BART2 rhetoric flying around), but I didn’t realize quite how good. While the I-5 alignment is the cheapest rail alignment and the most cost-effective I hope ST chooses 99 or Paine Field.
      2. In a sea of awful Eastside alternatives the UW-Redmond alignment jumps out. If connecting to a UW-Ballard line significantly boosts ridership we could have a winner for ST3. It also answers the question of what to do with 520 bus service. The downsides are it only really adds S Kirkland P&R as a new dot on the map and the challenges of crossing the ship canal to 520 may prove insurmountable.
      3. The elevated option for UW-Ballard via Fremont looks pretty good.
      4. Downtown-Ballard isn’t going to look good by cost-effectiveness metrics. In theory DEIS ridership numbers might be better with updated population projections and by extending the line to IDS.
      5. Serving Alaska Junction directly is not very cost effective. All options are expensive for little ridership.
      6. The Burien-Renton segment looks very promising. We should find a way to include this in ST3.
      7. The Delridge alignment solves a lot of problems. It provides fast service to Burien and Renton. It gets past the major choke points for much of West Seattle and is the most cost-effective rail alternative ST studied. The trick is convincing West Seattle to live with having to connect by bus to the rail line.
      8. Federal Way-Tacoma comes out looking much better than expected. As even the biggest rail fans here have been pretty negative on the prospects for such a line the cost effectiveness is suprising. Again while the I-5 alignments are the cheapest and most cost-effective I hope ST chooses one of the 99 alignments here. 99W performs pretty well and has much better TOD potential (such as it is) than the freeway alignments.

      1. Capital cost per ride is a metric used by the FTA. They analyze it over 40 years. All of these projects would be pennies per ride on that timeline. As we’ve pointed out elsehwhere – the eastside alignments options need to be redone. Also – the Ballard/UW and Ballard/DT numbers are low (2035) and the Tacoma/Everett numbers are high due to the PSRC 2035 model.

      2. Keith,
        I just wanted a relative basis for comparison. If I re-calculated on a cost per ride basis the alternatives would still compare relatively the same.

        While I respect the work you do, I’ll point out ST rejected crossing the Mercer Slough with rail during initial screening. I’m not sure your changes really address the environmental issues they found. Given density and land use on the Eastside the case for rail is going to be weak there. Even East Link does not perform well on a cost-effectiveness basis.

        I’m aware of the issues with the PSRC 2035 model. I’d be curious what the numbers for UW/Ballard and DT/Ballard would look like with an updated model.

        I’d also be curious what the Everett and Tacoma numbers look like with a revised model.

        Personally I think Everett is worth it but Tacoma can be served with BRT. Pierce money is likely better spent on things like extending Sounder to DuPont, DuPont/Tacoma DMU, and expansion of Tacoma Link.

  5. Cost per rider is an interesting and important metric, but I don’t think it is a good measure of the cost effectiveness of a system. It will, inevitably, suggest that streetcars are the best value. You could simply take many of the existing buses, paint them red, and then proclaim these new “red buses” as very cost effective. Most of the streetcar routes essentially do the same thing. They are slow, and simply mimic a bus route. Just as the 44 and 8 are really popular (and slow) so too are many of the proposed streetcar routes.

    A better measure would be the number of new riders. These are folks that wouldn’t take the bus in the past, because it is too slow. For a lot of routes, this number is really big.

    But that’s not all. In some cases the same riders will take the new system as the old one, but their experience is much better. Time saved per rider is a good measure. For example, someone who takes the 44 will definitely switch to a subway following the same route, and will save an enormous amount of time.

    Another metric is the number of routes that can be truncated but still provide much the same service. For example, the 41 from Lake City will no longer get on I-5 once the Northgate station is built. This is a lot of bus service that can be used somewhere else (or along that line). But it won’t make the ride much faster (for those going downtown) nor would it necessarily add much to ridership (for those going downtown). (In this case, since the North Link also serves Roosevelt, UW and Capitol Hill, it will add significant ridership).

    So, in general, you need to look at the system as a whole, not just the ridership on the new line. For example, a subway from Ballard to the UW will not make a bus travelling on Phinney Ridge any faster, but it will make a bus travelling that route much more valuable. If you add enough fast transit, then slow transit isn’t so bad. Eventually you get to the point that someone in, say, Greenwood no longer feels the need to use their car. They will ride the light rail a lot, but in many cases, take a bus in a different direction. These buses may run a lot more often, because of added service which was the result of the truncation mentioned in the last paragraph.

    All of this is to say that while this is a great post, and very interesting, it only shows a small part of the system. It in no way represents the value the way that a far more complex, far more complete analysis would yield.

    1. In other words, cost per rider is not the same as cost effectiveness, but is simply one small element of cost effectiveness.

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