Traffic Lab Ignores Sound Transit’s Tacoma Extension Problem

The Seattle Times’s Traffic Lab is the paper’s “ project that explores the region's policies that determine how we get around and how billions of dollars in public money are spent”.  A previous post detailed how, prior to the 2016 Prop 1 vote, the paper had recommended voters say “No to Sound Transit 3”.  Yet, their Traffic Lab  project continues to abide if not abbet Sound Transit spending billions on projects that will do nothing to reduce the area’s congestion and leave a huge debt. 

The latest example being the Traffic Lab abiding a June 12^th System Expansion Committee meeting detailing the Sound Transit approach to spending.  The meeting agenda “For recommendation to the Board”, included Motion No. M2025-31, adding up to $87,902,394 for a total not to exceed $181.555,740 for “Phase 3 project development services for the Tacoma Dome Link Extension" project.  

 

That funding was quoted as “Contingent on approval of  Resolution No. R2025-14 amending the Adopted 2025 Budget“ for the extension. (A budget they’d just approved in March) It authorized a $144,950,939 increase in 2025 budget from $112,388,021 to $257,388,960. (Sound Transit apparently doesn’t like reporting their spending in “millions”. ) 

 

It wasn’t clear with M2025-31 taking the additional ~$88 million, where the rest of the R2025-14’s additional $145 million in 2025 budget will be spent.  What is clear is that the Traffic Lab is abiding Sound Transit’s System Expansion Committee’s failure to recognize that the ST3 extension to Tacoma won’t reduce the area’s congestion. 

 

They don’t recognize Sound Transit’s problem with light rail trains limited to 4 cars.  Each 74-seat car can accommodate up to 148 riders, 592 per train. A 2004 PSRC study, funded by Sound Transit, concluded safe operation requires 4 minutes between trains, limiting capacity to 8880 riders per hour (rph). 

 

The Traffic Lab should “explore” how that limit affects benefits from theTacoma Link extension. Sound Transit’s latest ridership report for the 1 Line stations from Stadium to Angle Lake was 37,265 boardings, with 11,183 boardings at SeaTac. 

 

If 80% of the 26,082 boardings from the other nine stations were for routes into Seattle during the 3-hour peak commute, 1-Line boardings from Angle Lake to Stadium would average 6955 rph,  When 2 Line trains begin service early next year, Line I capacity will be limited to 4440 rph,  Thus, current Line 1 commuters nearer downtown will lose peak hour access to transit. 

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The extension to Federal Way later adds to the 1-Line boarders’ loss. A June 2024 Traffic Lab article claimed it would add, ”18,000 to 23,000 passengers.“  A similar analysis adds between 4800 and 6122 rph peak hour boardings on the route into Seattle, displacing even more current 1-Line boarders.

 

The bottom line is Sound Transit plans to spend millions on the Tacoma extension will further reduce current boarder access.  The Traffic Lab should recommend the Sound Transit Board delay funding the extension until next year when both Line 2 and Federal Way ridership effects on access for current  1-Line peak commute boardings are known.