Issues to Watch in the Seattle ST3 Alignment

Representative project alignments for the West Seattle and Ballard Link extensions (courtesy of Sound Transit)

Last month, Sound Transit announced an ambitious plan to wrap up alternatives analysis in 18 months for the Ballard-to-West Seattle ST3 plan. They're not promising that this will actually bring delivery forward from 2030 for West Seattle and 2035 for Ballard, but it should reduce risk of further slippage.

We have a pretty good idea of where this line will go, as indicated by the "representative alignment" at right. However, there are three interesting questions that will affect how much this project costs and how many people it serves. Remember also that money is time; a more expensive project increases risk of not having enough money in time, and slipping out opening day by a few years.

The ship canal crossing. In a guest post last month, Seattle Subway covered a lot of the issues. A relatively inexpensive bridge would include a drawbridge that would open fairly frequently. More height means fewer openings and more costs. This is a fairly clear tradeoff of budget and schedule risk for escalating train reliability.

Or, with more cost and technical risk, Sound Transit could tunnel under the crossing. Given the depths involved, this would mean running deep underground through a lot of Ballard. This limits the number of potential stations but also avoids various mitigation headaches.

Similarly, a relatively low crossing could replace the current Ballard Bridge, with adequate space for cars, pedestrians, bikes, and transit. SDOT loves this idea because it would take paying for it off their plate.

Midtown Station. The default is for this station is 5th & Madison, which is well within the walkshed of today's stations. Pushing the station further up Madison would bring dense neighborhoods and massive ridership generators into the system. Besides a pile of apartments, adding the hospitals and even Seattle University to the high-capacity transit network would right a historic wrong.

On the other hand, the downtown tunnel would have to be a few hundred meters longer, and the station would have to be deeper. Both would increase cost and risk. Moreover, it would require two undercrossings of I-5 instead of zero. Sound Transit performed this technically complicated operation once to build University Link, and has little interest in doing so again. Lastly, the known coalition in favor currently consists of the First Hill Improvement Association, a certain high-level transportation official, and me. That's not enough.

Alaska Junction. From well before the ST3 vote, the segment to West Seattle has always been advertised as an elevated segment. For fans of Chicago, Tokyo, or the Seattle Monorail Project, segments of elevated track are a delightful part of an urban scene and often a welcome respite from the rain.

However, it's worth observing that this region has never built elevated track through heavily populated areas. Sound Transit has always opted for an underground, retained cut, or surface alignment after receiving community input. Opposition even forced the monorail off Second Avenue, onto the current track on Fifth, before it died. Undoubtedly, some people will look at mockups like this West Seattle Blog photo and be horrified. Or they will ask - simplistically - why others are getting a tunnel and they are not.

That said, burying that track is essentially a beautification project, while the other modifications would be material improvements to the efficiency or usefulness of the train. So it's a little harder to justify spending more money and possibly delaying delivery.

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There is a very real tension between getting everything cheaply, and as soon as possible, and having light rail do everything we would like it to do. The coming process will be a strong indication of what people really care about most.