Sound Transit 3.5

Sound Transit 3 will see a 21st Century network of light rail connecting the whole of the  Seattle Metropolitan Area, from Everett to Tacoma north to south, Ballard to West Seattle within the city, and from out to the foothills of the Cascades west to east.

The one piece of the Metropolitan Area left out of the this network is Kitsap County, and it’s 260,000 (est.) residents, who are connected to Seattle through only through the Bainbridge, Bremerton, and Kingston ferries.  Ferries which run just once per hour, and which travel at speeds no faster than the mosquito fleet 100 years ago.

A proposed Sound Transit 3.5 connects Bainbridge Island and Bremerton to this network through a system of underground and under-Sound tunnels carrying the standard Sound Transit lightrail trains.  6.3 miles from Smith Cove to Bainbridge Island and 6.3 miles from there to the Bremerton.

Both train stations would be adjacent to the existing ferry terminals, connecting Sound Transit to the existing Kitsap Transit bus network, allowing most of the population of Kitsap County to reach Seattle and the rest of the Metropolitan Area in under half the time required today with a ferry.

Unlike the ferry, the trains could run every 15, 20, or 30 minutes, making commuting far more convenient for the thousands of Kitsap residents who work in King, Snohomish, and Pierce counties.

The challenge of this extension is, of course, Puget Sound.  The water is 600+ feet deep in the middle of the channel, necessitating a very deep bore tunnel.  Rail runnels at this depth with greater lengths have been built in Japan, connecting those islands with full-size, high-speed trains.  Similar tunnels for both rail and automobiles have been built in Denmark.  Over 100 years ago a pair train tunnels were built in New York City which are still in use today.  In short, no new technologies need to be invented to implement this plan.


This plan adds just two stations to the existing, approved ST3 plan.  In terms of size, scope, and projected passengers, it is most similar to the South Kirkland – Issaquah Link (see the ST3 page for details).  That extension is planned to be 11.75 miles long with at least four new stations.  No tunnels, but much of the line built on elevated track, and primarily serving suburban cities whose residents commute to work into Bellevue, Seattle, or other city centers around the region.

Total cost, timing, and other details are not yet known.  Kitsap County is not part of Sound Transit today, and as such its residents have never voted for nor pay taxes for any of the Sound Transit projects.  If this plan is to go forward, at least parts of Kitsap County would need to be added to the Sound Transit taxing district, if not the whole county, and the residents would need to approve this project as the residents of King, Snohomish, and Pierce approved ST3.

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