The Seattle Alignments and the Hidden Costs of West Seattle Rail

The Sound Transit 3 proposal package can roughly be divided into two parts, the suburban projects and the urban projects (the suburban projects could in turn be further divided into completing the “spine” and the eastside). The urban projects are the projects located in Seattle that are intended to serve Seattle residents. Of course, these projects will also serve suburban residents (at least much more so than suburban projects) because many Seattle neighborhoods are high-density employment centers that are not readily accessible by car, at least during rush hour.

My previous posts have mostly concerned some of the issues around the suburban projects, namely their poor cost-effectiveness and issues around freeway based alignments. This post intends to look at the issues around the urban projects, as well as propose a (in my view) superior alternative.

Let’s start by getting the facts straight. By the basic numbers, Ballard has by far the best ridership per dollar. Using the most recent numbers from Sound Transit, and basic assumptions of upfront payment of costs, 30 years of operation and a 20 year wait before service opens, Ballard has an extremely low cost per rider and is over 2.3 times more cost-effective by this metric as compared to West Seattle link as seen in Table 1 below.

Table 1:

Ballard WS Table 1

However, these numbers are misleading. The 129,500 figure for Ballard ridership includes ridership on South Link that will use the new tunnel, but only to go to/from the downtown stations to points further south. This is effectively ridership that would use the old tunnel under a no-build scenario. In order to compare West Seattle rail and Ballard rail apples to apples we need to use ST’s estimate of 67,000 riders that actually board or alight from the stations north of Westlake.

We also need to update the costs for both Ballard and West Seattle. Sound Transit maintains that the existing tunnel cannot have three separate lines (South Link, East Link and West Seattle Link) all sharing the same tunnel, as it would water down each branch’s headway to an unacceptably low 9 minutes. For similar reasons, Ballard Link also can’t use the existing tunnel. So in effective terms both lines require building the second tunnel and so the cost of said tunnel should be split evenly between the two lines for accounting purposes. Table 2 below shows these numbers under the assumption that the downtown tunnel is 1.25 miles at $750 million per subway mile.

Table 2:

Ballard WS Table 22

As you can see, the Ballard segment still grades out as more useful than the West Seattle segment. But the difference is closer to 33% better not 130% better. Combining these two columns we can derive the cost effectiveness of the Seattle rail projects as shown in Table 3.

Table 3:

Ballard WS Table 32

This $5.27 figure is ok, but these numbers can be improved upon with better routing decisions. I noted earlier that the West Seattle and Ballard lines required construction of a second Downtown tunnel. But this isn’t exactly true. Building a West Seattle line requires a downtown tunnel because only two of the three lines going south from the International district can use the existing tunnel. But the Ballard line doesn’t have to go all the way through Downtown. It can instead head east towards First Hill and the Central District. Because Sound Transit obstinately refused to ever study real transit to First Hill in this round, we don’t have exact counterfactuals, but let’s consider the Green Line in the image below, serving Madison, First Hill near Broadway and Jefferson, the Central District near 23rd and Jackson and Judkins Park station.

Green Line


For ridership, if we assume that Interbay gets about 7,000 boardings then on average an urban station for Ballard link is worth 12,000 boardings. So First Hill station would account for an additional 12,000 riders. The Central District and Judkins park are somewhat less dense so let’s estimate that combined they add an additional 12,000 riders bringing the total to 24,000 riders.

For costs, the net cost of a First Hill alignment over building a downtown tunnel would be about 1 mile of additional tunneling plus 0.6 miles of additional elevated track. At costs of $750 million per mile tunneling and $250 million per mile elevated (in line with the West Seattle rail alignment), the total net cost would be about $900 million, or about $1 billion dollars less than West Seattle rail. That leaves $1 billion dollars in Seattle’s budget, enough money to build direct access ramps between the West Seattle bridge and the SODO busway ($200 million) and completely grade separate the Interbay section ($400 million), with potential additional funds for infill stations, improved amenities around stations, a ship canal tunnel or other short-term improvements.

The alignment change also has an additional cost/benefit advantage. With the Ballard line not interlining with an existing Link line, the Ballard line can be automated (it could also have smaller station footprints and hence cheaper capital costs but I am ignoring that complexity for now). Automation comes with substantial operational efficiencies, as well as making it cheaper to maintain high frequency at off hours. Based on Vancouver Skytrain operational costs of $1.94 million per mile and Ballard and West Seattle link operational costs of $5.35 and 4.68 dollars respectively, automation should reduce operational costs by at least 50%, a substantial value improvement long-term.

Table 4 below outlines three scenarios. Ballard and West Seattle as proposed (Table 3), Ballard to Judkins Park automated with grade separation in Interbay and Ballard to Judkins Park light rail at grade through Interbay. Note that the automated scenario assumes that grade separation through Interbay will not add any additional riders, even though speed improvements through that section should increase ridership by a non-trivial amount.

Ballard WS Table 42

Based on these assumptions the automated line would increase ridership per dollar by 12%. Of course without better ridership estimates for First Hill, the Central District, grade separated Ballard and frequency improvements with automation, this figure could be too low or too high. For instance, if the First Hill segment drew 30,000 riders instead of 24,000 we’d see a 22% improvement over the current proposal with a $4.32 subsidy per rider. This analysis also ignores the cost/benefit of bus transit improvements for West Seattle* or how the remaining ~=$400 million dollars budgeted get spent. The analysis also ignores the costs associated with the disruption associated with building at grade along 15th ave. All these factors indicate that the Green Line would be substantially more cost-effective than what is proposed.

If your disappointed about the at grade segment in Ballard or the lack of service to First Hill, note that the fundamental problem is that service to West Seattle requires using limited resources inefficiently, as a large portion of the West Seattle alignment is redundant and West Seattle. though dense, isn’t dense enough to overcome that issue. Moreover, if you want to find funding for complete grade separation or a tunnel under the Ship Canal, the way to do it is prioritizing First Hill over West Seattle. I’d also add here that if Sound Transit is a regional organization then First Hill, with high employment density and a key regional asset in Harbor View Medical Center, represents a regional destination in a way that West Seattle, with mostly residential density and no regional destinations doesn’t.


*At most times of day bus service to the portions of West Seattle is extremely fast. During midday Rapid Ride C is scheduled to get between Alaska Junction (California and Alaska) and Downtown in 20 minutes on average. West Seattle rail would get between the Junction and Westlake in about 17 minutes, with most of the time savings coming between Alaska Junction and Delridge, where the C line makes several additional stops. But at peak, the West Seattle bus routes are prone to crowding and congestion on SR-99 and/or the West Seattle bridge. The simplest fix to that problem is to bypass that congestion by making the left lanes of West Seattle bridge HOV 3+ and then building off ramps from those HOV lanes to the SODO busway. The buses would then connect with Link at SODO and potentially continue north to Downtown.



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