Win-Win With a Wye Junction (or Spur)
The current ST3 plan
[UPDATE: PLEASE do not overreact to the original alliterative title. As the the text makes clear, I am agnostic as to whether this is a spur or a wye.]
The fundamental ST3 tension in Snohomish County is between extending to Everett via I-5 or via I-5/Paine Field/SR99 (see map above). I-5 offers the cheapest construction and fastest trip between Everett, Lynnwood, and points south. Paine Field is a major, if sprawling, jobs center and the most obvious destination in the area. It also contains Snohomish County's hopes for broadening its economic base beyond Boeing,* and has a chance to be the region's second commercial airport. The SR99 option, superior in many ways, is dead due to perceived impacts on existing businesses.
The downsides of Paine Field are the construction expense (which would push arrival in Everett to 2041) and the added distance (with a trip that is 10 minutes longer and a fare $.50 higher) for Everett-Seattle trips. Together these make it less competitive with other modes and cancel out the ridership gains from Paine Field itself. So the choice is: wait 25 years to serve relatively speculative development, or build faster via I-5 and forego much of that chance. Local leaders recently floated an idea to speed things up a bit (make it cheaper) by avoiding travel on SR 99 altogether. This might save a few years, but both exacerbates the lost development opportunities and likely increases travel time even further.
It seems straightforward, however, to get to Everett faster while also avoiding difficult travel time tradeoffs. A rail spur or wye junction allows Everett-Lynnwood travel to follow I-5. Moreover, ST could build that segment on essentially the same timeline as a pure I-5 alignment, delivering real progress faster. The Paine field branch would follow later as development necessitates, probably around 2041.
The deluxe version would build both approaches to Paine to reduce travel time, but this would add another I-5 segment to the existing plan and therefore be more expensive. A single spur to Paine effectively replaces the other leg of Paine Field with a segment along I-5, so that the construction cost ought to be lower than the current Paine Field plan. But the beauty of the branching is that it can be done incrementally as funding allows, while easily delivering the core objective of completing the spine to Everett.
The drawback to branching is reduced frequency, but in this case that's a small price to pay. One operational question is whether trains would follow a spur coming from Everett or from Lynnwood, or a wye that allows both. This ought to depend on where Paine Field demand comes from. You're welcome to your opinion on this, but really ST should look at future study results or local input to decide. Recall that the spine can readily support three minute headways. That leaves three possibilities:
- Spur from the North: 3 minutes through Everett, 6 minutes to Paine Field and Lynnwood, and additional trains south from Lynnwood to resume 3-minute headways.
- Spur from the South: 6 minutes each to Everett and Paine Field.
- Wye Junction: 6 minutes Lynnwood-Everett, 6 minutes Everett-Paine Field, 6 minutes Lynnwood-Paine Field.
There's no plausible scenario where these train frequencies are insufficient for demand.
ST hasn't studied a branch or wye at all, at least publicly. But it's self-evident that it would deliver rail to Everett faster. After construction ends, it makes rail trips more competitive with I-5 while still not abandoning the County's hopes for economic development around Paine Field. It even hedges the possibility of commercial airline service at Paine Field. A branched Everett line is a win-win for everyone involved, and Sound Transit should seriously consider this alternative.
* presumably intensifying the land use to be more conducive to transit.