As Seattle’s transit advocates, we often like to brainstorm about transit infrastructure because it generates discussions. It helps define what the region wants, and these discussions often drive politics. Light rail connections, BRT, and a second downtown tunnel are just some highlights of an ever-growing wish-list.
However, our focus on modes and infrastructure also leads us to overlook the actual objectives of these transit investments. We ask ourselves whether we want light rail and BRT, but rarely do we emphasize, “How quick and reliable should the system to be?” or “What is this system trying to accomplish?”
As a result, transit advocates are often surprised by operational deficiencies late in the process, leading to reactions like this:
“We have supported RapidRide and BRT from the beginning but Metro and the Council have let ‘BRT creep’ and politics take over, not what is best for riders. When RapidRide C and D lines open on October 1st we’ll have a glorified shiny new bus that is slower than existing service.” – STB
Part of the reason is because specific objectives are not clearly defined before transit is built. There were never defined travel times or reliability requirements from the beginning. We simply said “Build BRT” and assumed that everything would work out. As a result, decision makers have leeway to push for more infill stations to satisfy a few constituents, because why not? There was no legal requirement for what the actual travel time between A and B should have been. It’s easy to backtrack and modify service objectives that were never well-defined in the first place.
A few days ago, I posted on why light rail vehicles may not contain the performance necessary for regional transport (i.e. services that bridge suburban rail and low-end intercity rail). A brief overview of technical limitations was presented, but in order to keep the article short, the technical issues were simplified and details were omitted.
If you’re the type who enjoys a discussion about some technical challenges unique to light rail, here’s your article. We’ll discuss design characteristics that separates light rail from conventional heavy rail, focusing mainly on wheel-rail interactions. Then we’ll touch a bit on why higher vehicle performance is more complicated than just asking the vehicle manufacturer to tweak their trains for a higher design speed.
In part 1, we discussed how the limitations of our light rail system may impact its performance as a regional service. Now, we will highlight some potential issues within cities that we may face when our light rail capacity is adapted to serve high-demand suburban services.
Light rail’s need to provide high capacity and reliable mobility for the region is supported by its infrastructure. When the infrastructure means “surface running”, such as on MLK, high capacity (i.e. longer trains) is accommodated by large stations and reliability is provided by long stretches of track with uninterrupted travel. Although this means that mobility to and from the neighborhood is improved (regional mobility), accessibility within the neighborhood may be compromised.
With light rail expansion and planning well on its way, things look positive for rail transport in the Puget Sound Region. The momentum and demand for rail-based transport in the region appears higher than ever, with residents beginning to realize that our current transport network is simply inadequate for the growth rate in this region. When a single fish truck can bring the region to hours of standstill, transport alternatives cannot come soon enough.
However, as with every major project, there is always a time to step back and once again look at the big picture. What type of transport objectives are we trying to accomplish? What kind of connections and services do we need?
But here is the biggest question that we need to answer before Sound Transit 3: What exactly are we building right now?
The simple answer is, of course, light rail. The more complicated answer is that we are building a regional light rail network.
And that could be a problem, because light rail vehicle technology is not intended for regional services. If Sound Transit pushes these vehicles to compete with cars between Everett and Seattle, or Tacoma and Seattle, it will have to find a delicate compromise between competitive travel times and travel time reliability. Let’s discuss why.
I threw together a couple of charts to visualize how passengers have been using some of the routes that may be impacted by the U-link bus restructure. The data is hosted on Metro’s “For Transit Geeks” section of their U-Link bus network restructure proposal.
Here’s Route 48:
Notice how the passengers accumulate approaching the University District (45th St/15th or 50th St/15th, depending on direction) and begin to diminish when moving away from it. Also notice the higher passenger turnover when compared to the long haul 255 and 545 below (vertical comparison between colored area and grey area).
Here’s Route 255:
And here’s Route 545:
Both the 255 and 545 accumulate riders at a rapid pace until reaching the 92nd Av/SR 520 stop when going toward Seattle, with a few more getting off at Montlake than getting on. On the return trips, the 545 loses more than half of its load at the NE 40th and 51st St stops while the load on the 255 trails off somewhat steadily until the end.
Metro uses slightly different stops to define segments depending on which way the bus is traveling (inbound vs outbound); take heed when comparing the charts for the two directions. This visualization might be a lot more interesting and useful with break downs by time of day, by trip, or even by stop, but it doesn’t look like Metro provides that level of data. Bear in mind this is data for the whole day and is really only useful from that perspective.
An improvement I can already see is running these again on the same scale y-axis to get a better comparison between the routes; my intent here was simply to look at loading behavior across individual routes.