Zach’s summary and analysis of the Tier 2 alternatives arising from Sound Transit and Seattle’s Ballard HCT study is excellent, and if you’ve not read it yet, you should do so. There are some good ideas and some less-good ideas among the options, and I’m sure by now, our regulars will have thoroughly digested them, but in this post I’d like to point out one option that I was hoping would have made it into the final analysis but didn’t, a variant of Corridor C.
First, I’d like to explain my criteria for a sensible downtown Seattle rail line, beyond the obvious ones of being frequent, direct, reliable and focused on areas of high ridership potential:
- It needs to be no worse than an existing express bus trip, including transfer time. Ballard’s express services are massively popular, but express service is expensive to operate, both in terms of operations (lots of deadheading) and capital (lots of buses that sit at the base twenty hours a day). Riders will revolt if we try to cut their service without offering them something at least as good. If we can cut the 15X, 17X, 18X and maybe the 28X in favor of better connecting services, that’s a shedload of buses we can reallocate to better all-day service at minimal cost.
- It needs to be grade-separated south of Denny. Lots of people worry about the top speed of transit service, but it’s not very important for in-city services (say, typical trips of less than ten miles, stops about every half-mile), because even a fully grade-separated train spends much of its time accelerating or decelerating for stations; frequency and reliability matter most. Assuming any of these lines will be both very frequent and reasonably reliable, the most important factor to minimize trip time is to avoid extended periods of very low speeds, e.g. slogging at-grade through the city center.
To the first point. The current scheduled time from 15th/Market to 3rd/Pine on the 15X is 19-21 minutes inbound in the AM peak. Supposing train headways of 10 minutes (i.e. a five-minute transfer penalty) and a couple of minutes of added walking, we need Market to Pine travel times below 15 minutes if we’re going to build a rail line worth getting out of bed for. Option C currently fails that test — but I think it could be fixed through much smarter design, at a plausible cost.
More after the jump.
I’d like to enlarge on the second point with some back-of-the-envelope arithmetic. Consider the section of 15th Ave between Harrison and Dravus, which is about two miles long, has a speed limit of 35 mph, and only one arterial crossing that’s not already an overpass, at West Mercer Place. Suppose that a train gets to spend 1.5 miles of that at or near its top speed, and that it’s capable, on an elevated guideway, of 55 mph. The travel time difference between grade-separated and at-grade is then about one minute*. North of Dravus, there is a median with no crossings, which could be fenced off to provide a fully-exclusive right of way until the train became elevated to connect to a new bridge. So when evaluating travel time on 15th and Elliott, between Uptown and Ballard, the additional cost of two miles of elevated or tunnel construction likely buys us only about a minute.
The section between Harrison and Pine is very different. Here it becomes very difficult to estimate the difference in travel time between grade-separated and at-grade, because an at-grade alignment is so complex to evaluate. We can, however, look at a proxy: the difference in travel time between buses in the Downtown Seattle Transit Tunnel and surface-running buses traversing downtown on 3rd Ave (both about one mile with five stops). Metro staff have previously told me that the downtown transit tunnel saves about five minutes per trip versus the traveling on the surface. Belltown and downtown are similar environments — full of cars, lots of signalized intersections, and chronically congested in the peak — and 3rd Ave is a busway in the peak period, which provides similar transit priority to an exclusive lane.
It seems to me, based on Metro’s experience, that four or five minutes is about what a passenger would save on the 1.5 miles (and two stations) between Harrison and Pine, if instead of running on the surface, Corridor C had a portal just south of Harrison, at the intersection of Western and Elliott, and ran in a cut-and-cover tunnel along Western, Denny and 2nd Ave. The current configuration of the Western/Elliott intersection includes an undevelopable sliver of land that could be used to provide space for the portal. I will put in a request in to Sound Transit to get more detail on travel times on the various sections of these corridors, but if this turns out to concur with their estimation methods, then the upshot is that this “Corridor C2 (15th At-grade/2nd Ave tunnel)” would significantly narrow the travel time gap (currently about six minutes) between Corridor C (15th At-grade) and Corridor B (15th Elevated), at a much lower cost than Corridor B.
Additionally, a tunnel in this area would make the alignment politically far easier to implement. The fate of general purpose traffic should not be a primary concern in designing exclusive transit rights of way, but the street grid around stations does need to function well enough to get reliable connecting bus service in direct contact with the station. The west end of Denny is already a traffic bottleneck (even more so than everywhere else on Denny!), where Western’s three lanes taper to Denny’s two, and several major roads converge at awkward intersections. The disruption caused by reducing Denny to one lane at the west end may render connecting transit service unreliable, and will create enormous political pressure to run the train in mixed traffic through this section.
I should be clear that this “C2” would not be my ideal rail line. I agree with Zach that Corridor D, a completely-separated alignment that serves Seattle Center, Queen Anne, Fremont and Ballard (especially if operated using driverless trains running every couple of minutes until late at night, a la SkyTrain) would be utterly revolutionary for this city, I think it is the best alignment on the merits, and I intend to advocate for it.
But, sometimes we have to make difficult choices, like whether to build N miles of awesomeness that will last forever, or to build 3N miles of something that gets the job done — for thrice as many people, for the next 50 years. If we’re going to contemplate thrifty at-grade options (with vehicles that require drivers), we should be smart about them. That means running at-grade where roads are wide and speed limits are high, and running underground in the city center, which is where surface transit goes to die. While I hope it’s not the final result of this process, I’m a little disappointed that such an option has not made it this far in the analysis, and frankly slightly scared that downtown at-grade options, which will not get the job done, are still on the table at this point.
* 3600 seconds/hour * 1.5 miles * (1/[35 miles/hour] – 1/[55 miles/hour]) = 56 seconds.