I have long thought that ST’s current bridge design was a mistake. Although I think that ST’s current design does a mediocre job of directly connecting to UW’s main campus it does a very poor job of improving access to the medical buildings as well as riders that are transferring to buses on Pacific.
Station area pedestrian improvements should have two objectives. Increasing safety and accessibility of the station. Since ST doesn’t have some futuristic technology to reduce distance the major way ST can improve accessibility is to improve directness of access by reducing the perceived effort or ‘impedance’. Safety is increased by grade separating pedestrians from cars. This is pretty obvious. Directness is improved by creating straight and direct links between the station and major destinations, in this case the main campus, medical buildings, and bus transfer points. This is exactly what ST’s current designs don’t do, especially for riders that are transferring to buses.
The three plans
Since I’m a numbers guy I did some back of the envelope calculations to prove my point. According to a study done in Singapore with their subway system researchers were able to create a weighted walking distance measure that can help predict where pedestrians will walk when they have multiple route options. The equation they came up with is below.
EWD = DISTW + 55.4NCROSS + 2.81NSTEP + 36.3NCONF
- EWD = equivalent walking distance (m),
- DISTW = actual walking distance (m),
- NCROSS = number of level road crossings,
- NSTEP = number of ascending steps, and
- NCONF = number of traffic conflicts along the walking route.
Because the context of traffic in the study looked to be a much less intensive than at the triangle, with most large roads already span by footbridges, I doubled the cross impedance factor (55.4 to 110) and used 55 for minor crossings. Thus for every major road a pedestrian cross they would rather choose to walk 109 ft or 54 ft respectively to avoid crossing that road. These values (impedance factors) simulate how pedestrians dislike obstacles. I know this is fudging the numbers but I think it is fair for a back of the envelope calculation. Thus please don’t read too much into the detail just look at the overall trends.
This are the real distances. Main campus distance is to where ST’s current footbridge sets down, medical building is the front entrance, NB and SB bus stops are those on Pacific currently, and possible 44 stop is directly across from the Link station on Mountlake Blvd. You can see most of my measurements here.
After applying the weighting equations, I ranked the solutions. Both vista plans out performed ST’s plan for directness, with the original vista plan doing best. I then calculated the directness of each option.
This is the crows fly distance divided by the weighted distance. A value of 1 is the best possible, with lower values worse. A value of .5 means that if you walk 200 ft to an object, you have walked an extra 100 ft because the route you took was circuitous.
This last table shows that both vista designs (the most recent one without a footbridge and the original vista design with a footbridge between the station, triangle and medical building) increase directness of travel, with the original concept improving it the most. To me this shows that ST’s current footbridge design needs to change. A big part of this is a re-evaluation of how important it is for pedestrian traffic to be grade separated from the Burke Gilman trail. This is the real sticking point and the reason that ST’s current design is so awkward.
To me it is more important to grade separate pedestrians from Mountlake and Pacific Ave, with the original vista design doing this best, both from a directness and safety perspective. Not only that, the UW triangle will be a future transfer hub, something ST’s current design does little to accommodate.
UPDATE: So I just pulled a NASA mistake and forgot that the equation was in metric not english systems. Embarrassing. This means that the equivalent distance of those options that have grade crossings will be even higher, ie worse. So… the original vista option is actually better than my calculations show.
UPDATE II: I wanted to add a caveat about footbridge safety. When I say that they are obviously safer I’m making the assumption that they go where everyone wants to go and they have an escalator for those ascending. If both of these conditions aren’t meet the probability that people will jaywalk increases. At which point the safety benefits of a bridge are outweighed by the increased risk of people jaywalking I don’t know. From the lack of literature I have found on the topic I would bet few know and it would be a very interesting research topic.