SEA Underground

The system was approved for construction in 1969, to be built alongside the new satellite terminals as the first inter-terminal train system in the United States.{{Cite news |last=Wells |first=Jay |date=June 11, 1969 |title=Port Awards Contract for Sea-Tac Airport Subway |page=80 |work=The Seattle Times}} It was completed in 1972 at a cost of $5 million and opened to the public in July 1973.{{Cite news |last=Lane |first=Bob |date=May 2, 1972 |title=Underground people mover: Sea-Tac subway zips along on test run |page=B5 |work=The Seattle Times}}{{Cite news |date=June 1, 1973 |title=United Air Lines to start using new airport facility |page=A16 |work=The Seattle Times}} That makes it the second oldest airport people mover system in the United States{{Cite news |date=November 2003 |title=Satellite Transit System Really Moving |work=Northwest Construction |publisher=McGraw-Hill |url=http://northwest.construction.com/features/archive/0311_Feature2b.asp |url-status=dead |access-date=February 13, 2008 |archive-url=https://web.archive.org/web/20060318041032/http://northwest.construction.com/features/archive/0311_Feature2b.asp |archive-date=March 18, 2006}} (after Tampa International Airport). The opening was delayed due to a dispute between the Port of Seattle and Westinghouse, the manufacturer of the system, over contracted costs.{{Cite news |date=March 7, 1973 |title=Airport Subway System 'Stalls' |page=5 |work=Computerworld |url=https://books.google.com/books?id=6vKdbvX5BU4C&pg=PT1 |access-date=March 27, 2018 |via=Google Books}}

The system opened in 1973 at a total cost of $14 million. The original system consisted of nine vehicles;{{Cite news |last=Green |first=Ronny |date=May 19, 1974 |title=Sea-Tac—it's growing into a city |page=11 |work=The Seattle Times}} an additional three were added in the mid-1970s. The system was designed to have a capacity of 14,400 passengers per hour and travel at a maximum speed of {{convert|27|mph}}.{{Cite report |title=Automated guideway transit : an assessment of PRT and other new systems, including supporting panel reports |last=The United States |date=June 1975 |publisher=United States Congress, Office of Technology Assessment |page=17 |access-date=February 17, 2021 |via=Princeton University |chapter-url=http://www.princeton.edu/~ota/disk3/1975/7503/750304.PDF |chapter=The Status and Potential of Automated Guideway Transit in Urban Areas}}

The original C-100 vehicles were built by Westinghouse and had a maximum capacity of 102 passengers.{{Cite news |last=Office of Technology Assessment |date=June 1975 |title=Who Owns AGT Systems? |work=Automated Guideway Transit: An Assessment of PRT and Other New Systems |url=https://books.google.com/books?id=tI9AuKexGLgC |access-date=February 13, 2008 |isbn=978-1-4289-2523-6}} The average travel time for the two loops was 3.3 minutes, and 1.8 minutes on the shuttle, and each vehicle was estimated to amass {{convert|47000|mi|km}} annually.

In 1999, the Port of Seattle authorized $142 million to completely overhaul the entire SEA Underground system.{{Cite news |date=November 11, 1999 |title=Trains at airport to be replaced |page=B2 |work=The Seattle Times |url=https://infoweb.newsbank.com/apps/news/openurl?ctx_ver=z39.88-2004&rft_id=info%3Asid/infoweb.newsbank.com&svc_dat=AWNB&req_dat=0D1C147B217EB320&rft_val_format=info%3Aofi/fmt%3Akev%3Amtx%3Actx&rft_dat=document_id%3Anews%252F0ED1C87185374F35 |access-date=August 18, 2022 |via=NewsBank}} The overhaul included all aspects of the system including trains, controls, power supplies, stations, emergency ventilation systems and maintenance shops. The upgrade and modernization was completed in 2003. The line now uses Innovia APM 100 vehicles (a modernized version of the original C-100 vehicles) with the Cityflo 650 CBTC (communications-based train control) system for its automated operation.{{Cite news |date=Spring 2005 |title=Sea-Tac Satellite Transit: Complex system delivered under schedule, budget |work=Centerlines |publisher=Airports Council International-North America |url=https://www.aci-na.org/static/entransit/SEA_Transit_Facilities_Spring2005.pdf |url-status=dead |access-date=February 13, 2008 |archive-url=https://web.archive.org/web/20090810122225/http://aci-na.org/static/entransit/SEA_Transit_Facilities_Spring2005.pdf |archive-date=August 10, 2009}}

The Port of Seattle renamed the system to SEA Underground in March 2022 and assigned new names to the lines using colors: Green Line, Blue Line, and Yellow Line. Those colors were also added on the walls next to and behind the station doors.{{cite web |last1=Ciceron |first1=Dianne |date=March 17, 2022 |title=All Aboard the SEA Underground |url=https://www.portseattle.org/blog/all-aboard-sea-underground |website=Port of Seattle |access-date=March 21, 2022}}

File:Main Terminal North, SEA Underground 2022-07-23.jpg

SEA Underground is located within secure areas of the airport. The system consists of six stations serving each of the four gate concourses extending from the main terminal (Concourses A, B, C and D), and the North and South Satellite terminals. Each station is equipped with platform edge doors. The system consists of two loops serving the satellite terminals and a third line connecting the two loops in the main terminal.{{Cite web |last=Port of Seattle |title=Sea-Tac Airport Transit System |url=http://www.portseattle.org/Sea-Tac/Maps-and-Directions/Documents/Final-Transit-System.pdf |url-status=dead |archive-url=https://web.archive.org/web/20151003041623/http://www.portseattle.org/Sea-Tac/Maps-and-Directions/Documents/Final-Transit-System.pdf |archive-date=October 3, 2015 |access-date=October 2, 2015 }}

• The Green Line (North Train Loop) is {{convert|4100|ft|m}} in length and has stations in the north end of the Main Terminal (near Concourse D), Concourse C and the North Satellite (N gates).
• The Blue Line (South Train Loop) is {{convert|3700|ft|m}} in length and has stations in the south end of the Main Terminal (near Concourse A), Concourse B and the South Satellite (S gates).
• The Yellow Line (Shuttle Train between A and D Stations) is {{convert|1000|ft|m}} in length and has stations at both the north end of the Main Terminal (near the D Concourse) and the south end of the Main Terminal (near the A Concourse), and serves as a connection between the North and South Terminal Transit Loops.

The system has 21 APM vehicles, with about 13 in service at any given time: two 3-car trains on the Green and Blue Lines and a single car on the Yellow Line.{{Cite news |last=Brown |first=David Parker |date=December 9, 2016 |title=Behind the Scenes of Seattle-Tacoma International Airport's People Mover System |language=en-US |work=Airline Reporter |url=https://www.airlinereporter.com/2016/12/behind-scenes-seattle-tacoma-international-airports-people-mover-system/ |access-date=August 17, 2022}} Approximately 40 percent of Sea-Tac Airport passengers use the SEA Underground system. Maintenance is generally conducted on weekends after cars are moved into one of two shops via a lateral transfer table.{{cite news |last=Drawhorn |first=Omie |date=June 20, 2024 |title=Riding the Rails with SEA Underground's Maintenance Crew |url=https://www.portseattle.org/blog/riding-rails-sea-undergrounds-maintenance-crew |publisher=Port of Seattle |accessdate=June 24, 2024}}

The system has a 99.9% uptime rate. When track maintenance is required on the Green and Blue Lines, the work is typically done overnight, and a single train operates in a shuttle mode. If the system experiences a loss of traction power, cars have enough power storage to allow them to reach the next station. While most APM systems are operated by the system builder, the Port of Seattle is one of the few owners that also operate and maintain their APM system. The Port estimates that this arrangement results in a 40% savings in maintenance costs.

As part of its 2003 renovation, public art projects were included in the scope of the project. The main terminal's south station features a series of 56-plus flowers cast of aluminum and aluminum/resin mix created by Nancy Blum.{{Cite web |title=Art at Sea-Tac: Satellite Transit System: Nancy Blum |url=http://www.portseattle.org/seatac/art/satellite.shtml#blum |url-status=dead |archive-url=https://web.archive.org/web/20080201161455/http://www.portseattle.org/seatac/art/satellite.shtml#blum |archive-date=February 1, 2008 |access-date=February 4, 2008 |website=Port of Seattle}}

In the main terminal's north station is a series of nine paintings created by Karen Ganz representing various travelers.{{Cite web |title=Art at Sea-Tac: Satellite Transit System: Karen Ganz |url=http://www.portseattle.org/seatac/art/satellite.shtml#ganz |url-status=dead |archive-url=https://web.archive.org/web/20080201161455/http://www.portseattle.org/seatac/art/satellite.shtml#ganz |archive-date=February 1, 2008 |access-date=February 4, 2008 |website=Port of Seattle}}

{{Portal|Aviation|Trains}}

• List of airport people mover systems

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{{Commons category}}

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{{North American airport people movers}}

Category:1973 establishments in Washington (state)

Category:Airport people mover systems in the United States

Category:Innovia people movers

Category:Port of Seattle

Category:Railway lines opened in 1973

Category:Seattle–Tacoma International Airport

Category:Transportation in King County, Washington