Sound Transit is making substantial progress on the Northgate Link and South Link extensions. This week, two key milestones were reached with tunneling work and the placement of final elevated guideway segments.

Pamela, one of two tunnel boring machines (TBMs) mining the underground Northgate Link extension, broke through to the Roosevelt Station Station pit. Her arrival marks the second TBM to reach the station this year. Pamela was initially launched in November from the Maple Leaf Portal near Northgate Mall. Since then, she has traveled southward for the first 1.5 miles of her 3.4 mile trip to University of Washington Station. Pamela will take a temporary break at the Roosevelt Station site for repairs and refurbishment until being relaunched. The TBM will continue onward to the next station pit site located in the University District.

Northgate Link extension schematic.
Northgate Link extension schematic.

In March, Pamela‘s sister TBM Brenda arrived at the Roosevelt Station site after eight long months of mining. Brenda has already been relaunched from the Roosevelt Station site and is expected to arrive in the University District later this fall. Both TBMs should reach University of Washington Station (near Husky Stadium) some time in mid-2016. Sound Transit expects contractors to wrap up interior tunnel work like power and track, fire and life safety, and signaling and communications systems some time in early 2018. However, service will likely start three years later in 2021.

The Northgate Link extension is a $2.1 billion, three-station extension. Two stations (University District Station and Roosevelt Station) will be underground while one station (Northgate Station) will be elevated. Sound Transit is projecting 35,000 daily riders to access each of the three stations (University District: 12k; Roosevelt: 8k; and Northgate: 15k). For riders boarding from the University District, travel time to Downtown Seattle will be as little as 8 minutes while Northgate is even shorter at 5 minutes. Today, both of these trips are considerably longer with most in excess of 20 minutes and 15 minutes, respectively. But perhaps even more dramatic is the project trip time from Northgate to Seatac Airport. Station-to-station trip time is estimated to be 47 minutes one way. That trip would take 1 hour and 4 minutes and two buses under the best circumstances today.

University District Station bulk rendering.
University District Station bulk rendering.

Sound Transit has a number of fascinating tunneling statistics that transit nerds will appreciate:

  • By completion, more than 500k cubic yards of earth will have been excavated by the two TMBs;
  • The cutterheads of each TBM are 21.5 feet in diameter (about two stories high);
  • 7,200 concrete rings will line the tunnel walls (these are placed as the TBMs move forward); and
  • Each TBM is more than 300 feet long and weighs 600 tons.

After two years of construction, Sound Transit is nearing completion on the South Link extension from Seatac Airport to South 200th Street. Work on the the 1.6-mile double-track extension has progressed rapidly considering that construction only began in May 2013. Sound Transit’s contractors have largely focused on the construction of pylons and elevated guideway, but extensive work has been done on Angle Lake Station near South 200th Street. Earlier this week, construction crews hoisted the last few concrete guideway segments into place on the alignment to complete the connection to the Seatac Airport Station terminus.

Once opened, Angle Lake Station will act as the new interim terminus of Central Link until the Kent/Des Moines extension becomes operational in 2023. Angle Lake Station is projected to have more than 5,400 daily boardings by 2018. Trains departing from the station will head northward and terminate at University of Washington Station. Sound Transit has estimated travel times to be 37 minutes to Downtown Seattle and 43 minutes to the University District. Frequency during the weekday peak will be relatively high at every 6 minutes. The station itself will be elevated and come with a number of amenities and services:

  • A 1,050-stall parking garage for drivers and vanpool riders;
  • Covered waiting areas and platforms;
  • A transfer area for local routes and the RapidRide A Line;
  • Secured bicycle storage; and
  • Local improvements for pedestrian and bicycle access as well as site landscaping and artwork.

Sound Transit reports that the project is currently running well under budget by $20 million. Total project costs are estimated to be $383 million. The extension should open in fall 2016, about a half-year after University Link to the north. In the meantime, contractors have plenty of work ahead of them before trains get rolling. Construction crews will now set the remaining rails, erect overhead catenary wire systems, and install signaling and communications systems.

Aside from these two projects, the latest update from Sound Transit indicates the University Link–the extension from Westlake Station to University of Washington Station–is 95.3% complete. Station construction is still ongoing at Capitol Hill Station. Meanwhile, testing and minor work also remains before the extension opens in early 2016.

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Stephen is an urban planner with a passion for promoting sustainable, livable, and diverse cities. He advocates for smart policies, regulations, and implementation programs that enhance urban environments by committing to quality design, accommodating growth, providing a diversity of housing choices, and adequately providing public services. Stephen primarily writes about land use and transportation issues.