In the latest ST3 study concept, with a one-seat ride from Ballard to the Rainier Valley, there are a total of 14 sensible transfers in Seattle: two at Sodo, between West Seattle and Rainier Valley; four at International District/Chinatown, between Redmond and either West Seattle or Rainier Valley; two at Westlake, between Ballard and Everett; and six equally appropriate at two or more of those stations, because the direction of travel through downtown is the same. In a discussion with ST spokesman Geoff Patrick and other ST staff, STB learned about some preliminary concepts for how these transfers might work.

Of course, these concepts are very preliminary. The Board hasn’t even committed to a second tunnel, much less accepted detailed transfer concepts. But they do indicate a staff thinking hard about how to avoid the transfer mistakes of the past.

At International District, Sound Transit would excavate a cut-and-cover station under 5th Ave S, directly east of the current station (see the figure at right). The new station mezzanine would connect directly with the northbound platform in the existing stop. From the existing southbound platform, riders would climb to the surface, decline to the northbound platform, and then work over to the Green Line mezzanine without having to cross the street.

This concept is miles ahead of past station designs, and significantly reduces the frustration of Sound Transit’s refusal to consider a center platform at the current ID station. Direct street access to the Green Line Mezzanine would be a nice addition. But then Oran developed a far better concept, with a tweak from me, shown at right. The beauty of this configuration is that it maximizes the ease of the most important transfers at International District, which are between East Link and either West Seattle or the Rainier Valley. I imagine a setup like this would be a substantially more complicated project, probably more expensive and with more service disruptions during construction, and I suspect Sound Transit will find a reason not to do it. But it’s worthwhile to put the optimal configuration on the record.

Although the all-surface transfer at Sodo is much more straightforward, switching Central Link to the Green Line and a new tunnel will require significant work in the busway corridor. As Geoff Patrick put it:

Subject to refinement during the environmental review and design processes, the existing tracks north of Massachusetts would be reconfigured to connect with a new alignment proceeding north to the vicinity of the current location of Stadium Station where it transitions into a new tunnel. The existing Stadium Station would be relocated to the west side of the E3 Busway and would serve the West Seattle to Everett line through the existing Downtown Seattle Transit Tunnel. All of the specifics will be subject to close review during the preliminary design and environmental review process, during which alternatives will be developed in consultation with the public, impacts will be evaluated and mitigation will be identified.

At Westlake, the Green Line will be traveling (roughly) North towards South Lake Union while the Blue and Red lines travel (roughly) East towards Capitol Hill. As you can see in the figure below, the green line tunnel would pass to the and below of the existing station. Stairs or escalators would connect the (mined) new mezzanine with either platform of the existing station. A transfer of this quality is crucial, as a decent Westlake transfer in this context fulfills the longtime wonk dream of a congestion-free transit connection between Lower Queen Anne, South Lake Union, and Capitol Hill, the informally discussed “Metro 8 Subway.”