The continued debate in ST3 is whether to build the West Seattle line above ground or in a tunnel. The residents want a tunnel, but the existing plan and budget is above ground.
The proposed ST5 extension to Kitsap County is best connected to the Sound Transit system in West Seattle. Puget Sound is not at deep between Alki Point and Bainbridge Island as it is between Smith Cove and Bainbridge Island.
If ST3 were to add the proposed Kitsap Extension now, before finalizing the West Seattle line, then not only would there be a new, compelling reason for the West Seattle connection to be underground, but as long as a tunnel boring machine is needed to cross the Sound, that tunnel could connect downtown Seattle to Delridge directly, without the need of a new bridge across the Duamish and without the need for the line to connect to Sodo and Stadium Stations.
In fact, with a deep bore tunnel West Seattle / Delridge could be greatly shortened, popping up in Seattle in the empty hole in downtown Seattle adjacent to the existing Pioneer Square station (see above).
Moving the interconnect from the International District to Pioneer Square would alleviate alleviate the need to disrupt the International District businesses for years, all while putting a tunnel boring machine in downtown Seattle to dig the second downtown tunnel for the line that connects to South Lake Union, Seattle Center, and Ballard.
The fate of that second tunnel is unclear here due to the drop in ridership and loss of funding caused by the pandemic.
Rather than finding corners to cut and rather than pushing out the completion date for ST3, it’s time to look at all the mass transit infrastructure the metropolitan area will need by 2050 and blending those needs into a better plan than ST3.
Step one for that is adding Kitsap County, turning ST3 into ST5.