Ballard to Tacoma? Sound Transit Looks to Split the Spine

One possible ST3 scenario (map by the author)

Among the dozens of projects and corridor studies presented at the ST3 Board Workshop yesterday, perhaps the most interesting new concept was an operational idea to effectively split the spine into more manageable corridors. Though unspoken by regional leaders, the light rail spine has always been more of a political conception than an operational one, as running a pure Everett-Tacoma line was always going to be a stretch (at best). Such a line would be over 2 hours end to end, require additional maintenance facilities, restrict scheduling options, and likely require operator changes on every single train.

At the same time, Sound Transit has recognized something that advocacy groups such as Seattle Subway have long noted, namely that a new downtown tunnel for a Ballard-West Seattle line would waste that tunnel's capacity, hence Seattle Subway's idea for a bus-rail tunnel instead. Not at all keen on that idea but cognizant of the operational realities, Sound Transit has come back with an exceedingly ambitious and exciting proposal (see my unofficial map above):

• Blue Line: Everett to Redmond (6 Minute headways)
• Red Line: Everett to West Seattle (6 Minute headways)
• Green Line: Ballard to Tacoma (6 Minute headways)
• 3 minute headways between Everett and International District/Chinatown

South from International District Station (IDS), the Red Line would serve Stadium and Sodo in new tracks west of the current stations before running elevated to West Seattle, terminating either at Alaska Junction or White Center. The current station at Stadium would be demolished and rebuilt as part of Green Line construction. The Blue Line, meanwhile, would head east as planned to Mercer Island, Bellevue, and Redmond.

The Green Line would serve Tacoma, Federal Way, SeaTac, the Rainier Valley, Downtown Seattle, South Lake Union, Queen Anne, Interbay, and Ballard. From a rebuilt Stadium station, the line would enter an expanded International District Station via cut-and-cover construction on 5th Avenue South. IDS would essentially be a 4-track station, potentially with cross-platform transfers between southbound Green Line and northbound Red and Blue line trains. North of IDS, the Green Line would run in a new deep bore tunnel through Downtown to Queen Anne, with stations at 5th/Madison, at Westlake (beneath the current station), at Westlake/Denny, and at Queen Anne/Mercer. There the tunnel would emerge and run elevated through Interbay to Ballard.

Sound Transit's Ric Ilgenfritz walked the Board through this idea, and it was clear from the presentation that Sound Transit prefers this concept to a standalone Ballard-West Seattle line. Though there are drawbacks, such as permanently leaving out Belltown and requiring Snohomish and North Seattle riders to transfer to reach the Rainier Valley and Sea-Tac, etc, the operational benefits are immense:

• By freeing the Northgate-IDS core from the Rainier Valley line, you could potentially increase frequency beyond 3 minutes and improve reliability to near 100%.
• Transfers would be world class at both Westlake and IDS, both contained within their respective stations.
• Travel between South Lake Union and Capitol Hill (the "8 subway") would be effectively solved with a simple underground transfer between a 6-minute line and a combined 3-minute line.
• The new Madison station would connect with Madison BRT for additional eastbound options. It might be even better a couple blocks east as a true First Hill station, but that's a post for another day.
• The new tunnel would rebalance passenger loads, taking pressure off the current tunnel while better utilizing the new tunnel.
• This option allows ST3 to be built out with 4 maintenance bases instead of 5.
• Operations are much simpler, and labor much more reasonable, when no single line exceeds 90 minutes end-to-end running time.

What do you think?