Are ST3’s Deep Stations a Problem?

Like most observers, we were shocked when we saw how deep Sound Transit's station plans were for the new downtown tunnel. Beyond engineering complexity, deep stations can present a problem for riders: getting to and from the surface isn't always easy and fast. This concern is particularly amplified by the location and intention of these stations, downtown stations are expected to be high-ridership and a lot of trips will be short.

Before the pandemic, a large portion of trips in the current Downtown Seattle Transit Tunnel (DSTT) both started and terminated in the tunnel. We would expect demand for these kinds of trips to be even higher when the new ST3 tunnel opens, which adds high value tunnel destinations at Denny, South Lake Union, and Seattle Center. That demand might look elsewhere if the rider experience is bad, adding 5 minutes to both sides of a short ride just to get to the platform doesn't really make sense for riders. The scale of the investment detaches from the utility of the infrastructure. In short - this tunnel is very expensive and better be very good too.

So, is it possible to have deep stations but maintain a good rider experience? The center of this issue for riders is about speed and reliability to get to and from the train platform. The depth of the station isn't an issue if you and 200 of your fellow riders can get from the platform to the surface in a couple of minutes. That means that escalators are pretty much out as a primary means of getting people in/out of a station that is over 100 feet deep. Sound Transit's DEIS presented the following depth options for each station: Midtown: 140-190, Westlake: 125-140, Denny 100-125, SLU 85-120, Seattle Center 85-120. That means it's very likely that every station in the new DSTT would fail riders if the primary conveyance is escalators.

Midtown station, Sound Transit. Riders are skeptical.

So... we need to talk about elevators. It's possible for elevators to move a lot of people, fast. It helps that what we ask transit elevators to do is so much less complex than what an elevator in a building has to do. Transit elevators are almost always just about going from one place to one other place. But let's be clear, the one place should be the surface and the other place should be the platform, yet some of the options presented include a deep elevator to a mezzanine that then requires escalators to reach the platform. Just... no. I'm sure we're not the only ones imagining getting to the mezzanine just to find the escalators to the platform out of service.

Worse, Sound Transit doesn't have a great track record on this front. The elevators at Seatac are a full on maintenance disaster and Mount Baker isn't far behind. Our only example of a deep station that relies on elevators is Beacon Hill and those elevators leave a lot to be desired. Some of the issues are larger ,such as maintenance problems leaving too few elevators in service. Some of the issues are smaller but really matter: It shouldn't be necessary to wait for the elevator doors to close to call another elevator to the platform while a crowd of people waits. Yet this is the kind of substandard experience Beacon Hill riders deal with regularly.

The worst of both worlds. Image The Urbanist.

So what does a good elevator experience look like? Since Sound Transit's future proposed ST3 stations are going to be using 2020's technology, we'll go a step further - beyond mastering the basics - elevators should be automated to be called to the platform when a train arrives. And yes, directly to the platform, not to another mezzanine with escalators. On this front Beacon Hill station got it right.

As an aside, the new stations at Westlake and ID should have both platform to surface elevators capable of moving a lot of people and escalators for transfers to the other tunnel that allow riders to use the existing escalator exits as well. Multiple options and pathways are a very good thing to have at these two extremely high ridership transit hubs.

All that said, we're still skeptical of deep stations. The best station in the current system for riders is International District Station. Grade separated and shallow, open, easy to access, easy to see what's happening on the platform from most entrances and most important: Very fast to get to the platform from the surface. If it was center platform and didn't leave part of the southbound platform open to the elements, it would be close to the platonic ideal station for riders. We had hoped that a shallow station that is level with the existing platform under 5th was possible but Sound Transit didn't study it. We're also curious if it's possible to build a shallow 4th aligned station that goes over the existing DSTT tunnel when it crosses to 3rd.

We've requested more detailed information from Sound Transit about what is driving these lines to be so deep but haven't received a reply, other than the same high level reasoning repeated elsewhere: building depths and tie backs. It seems like a shallow line directly under the 4th or 5th right of way is possible, but without more information we don't actually know why it's not. Though there are engineers involved in our group, we won't play armchair engineer on this. That said, we know it's worth asking if obvious things were looked at because sometimes process can get in the way of engineers doing their best work.

So, are deep stations a problem? Not if people can reliably get to the platform fast. If there are truly no other options but to make the new downtown tunnel deep, the details of how people will get to the platform and how much time it takes becomes critical. This new tunnel isn't just for long suburban trips, it has to serve all riders well. We should have this as a minimum expectation from Sound Transit for such a critical piece of infrastructure.