[UPDATE: To be clear, ST is not dismissing Sounder ridership. The author is.] One unexpected contention point in the ST3 plan is the precise location of Chinatown Station. The reference alignment places the station under 5th Avenue, steps from the existing station. However, Chinatown business that have already suffered through streetcar construction have no interest in disrupting business access yet again, although in the long run the neighborhood would presumably benefit from a closer station. SDOT thinks a 4th Avenue alignment may fund some work they already do there. Sound Transit, reasonably, is most focused on the easiest and cheapest way to complete the project. As usual, no stakeholder is primarily interested in the convenience of future riders.

This convenience matters: seamless transfers encourage ridership, and thousands of people will be switching between Link lines at this station every day. Indeed, this will happen as early as 2023 when East Link opens, but Sound Transit has already added an unnecessary escalator and flight of stairs (or two slow elevators) to that transfer experience to avoid a minor capital project.

Another consideration is Sounder, though about an order of magnitude smaller in ridership than Link by the time ST3 opens. Amtrak is probably another order of magnitude below that. But what is the right answer for riders? Sound Transit has four concepts for how these transfers might work: under 4th or 5th Avenue, either cut-and-cover or mined.

The 5th Avenue cut-and-cover station (above) creates more disruption for the neighborhood than the mined option, but it drops riders much closer to the surface. Northbound and southbound riders at the new station would be the same distance from the old station, though the lower one would have a longer ride to the surface. Sounder transfers are not a priority in this alignment. ST says the upper platform would be the northbound line, because it “best facilitates northbound-to-northbound transfers between the West Seattle-Everett line and the Ballard-Tacoma line, which is generally expected to be the highest volume transfer during the highly-concentrated AM peak period.”

ST fears that a side-by-side alignment, given the constraints of foundations under 5th, might not have the needed platform capacity.

The mined station (at right) plunges riders about 200 feet below the road, but construction would be less visible on the surface. This is deeper than Beacon Hill and much deeper than UW, implying elevator-only service. This may not be suitable for a high-ridership station. Transferring riders wouldn’t have to go all the way to the surface, although the complexities of emptying half of a crowded elevator are probably worse than simply taking it to the surface.

Under 4th, a cut-and-cover station would provide easy access to the current southbound track, but the northbound track requires going to the surface. Although the schematic isn’t clear, it appears to be possible in theory for the mezzanine to allow access to Sounder without having to cross 4th Avenue, though a surface path is inevitable. ST confirmed they are also looking at a stacked configuration here, as the BNSF retaining wall under 4th limits the available space.

Finally, a mined 4th Avenue station requires elevators, so the mezzanine provides little value while worsening crowd flow. Once they’re on the elevator, you might as well have them walk through the beauty of Union Station instead of a rat maze.

Of the four options, it’s clear that a shallow station is better for future riders. A crowded train at a downtown station and major transfer point is likely to overload the elevators and cause long waits. Moreover, a mezzanine stop that facilitates transfers is likely to cause further delays if large enough to accommodate large crowds.

Meanwhile, the two shallow options are hard to reason about, partly because the stacked and center-platform configurations may be applicable under either avenue. It’s even hard to figure out which transfers matter. Clearly, Chinatown will be the focus for transfers between Bellevue and both SeaTac and West Seattle; but other north-south and south-north transfers are best made elsewhere.

As for north-north and south-south transfers, we don’t have enough information. To get from SeaTac to Northgate, one might transfer at the first opportunity, Sodo; but then there is half as much frequency as there is further north. Chinatown is an option, but depending on the relative speeds in the two downtown tunnels, and the transfer experience at Westlake, that station may work out better. There is similar uncertainty for South-South transfers.

In all, it’s hard to objectively measure the tradeoff between being really close to Link and really far from Sounder (5th), or being a medium distance from both, even though the Link transfers are more important. The difference to riders between these concepts is not all that large. If the contest turns out to be damage to downtown business vs. ease and cost of construction, this seems like a difference that can be patched with money. ST passes on some of the savings from the 5th avenue project to local businesses, they survive the construction period, and ST doesn’t get bad headlines for delays and overruns.