Satellite Transit System Renewal &
Replacement
Seattle-Tacoma International
Airport
Item No. 10a_supp
Meeting Date: July 23, 2024
Historical Context - Existing STS
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• Satellite Transit System (STS) consists of two loops (North and South Loop) and the shuttle connector.
• STS helps passengers travel to their gates quickly in 2-5 mins and access N and S Concourses.
• STS carried approx. 28 Million Passengers in 2023.
STS Program Goal/ Purpose
• Timely and cost-effective renewal and replacement of
STS is required to continue operation and maintain
efficient airport.
• The Preferred Solution will accommodate near and
long-term demand considering:
1. Replace end of life vehicles and rehabilitate aging
STS tunnels.
2. Minimize impact to existing STS infrastructure and
operations during construction.
3. Enabling project constructing a new pedestrian
connector between N and D Concourse
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History of STS
• 1973: SEA’s STS was first implemented with 9 vehicles and
was one of the first STS in the US.
• 1982: 12 additional vehicles were added, totaling to 21
vehicles.
• 2003: STS was modernized with new 21 vehicles and radio-
based train control system.
• 2020-2027: Replace train control system as it is approaching
end of useful life (in construction).
• 2030-2035: STS vehicles will reach the end of useful life
(reaching design mileage of 1 million miles) and must be
replaced.
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Existing STS Conditions and Challenges
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Major rehabilitation/ replacement
of STS tunnels is needed to extend
useful life past 2030
North and South Loops cannot serve
the forecasted passenger demand
without modification
Vehicle service life will end between
2030-2035
Existing vehicles are discontinued
Standard STS vehicles on the market
cannot fit in the existing tunnels
Future GrowthAging STS Tunnel
End of Life - STS Vehicles
Existi ng STS Loops
PDD Purpose
• Project Definition Document (PDD) is
required as a bridging document before
project design.
Project Scope
• PDD will be used as a starting point to
refine the project concept to approx. 15%
design level of the Preferred Solution.
• PDD will address sustainability goals.
• The total duration of PDD is 112 weeks.
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PDD to address existing STS Conditions and
Challenges
• Develop different
concepts for STS
system replacement
• Evaluate alternative
structural rehabilitation
concepts
• Develop preferred
concept to 15% Design for
STS tunnel and North
Pedestrian Connector
• Review previous study and
analyze existing conditions
• Perform additional site surveys
• Conduct Risk Assessment
Future Growth
End of Life of
STS vehicle
Aging Tunnel
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STS Replacement Program Timeline
2024
2030
2036
PDD
Pre-
design/Engineering
Design/Vehicle
Procurement
Construction Project Completion
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Requested Action
Request Commission authorization for the Executive Director:
1. Advertise and execute contracts for technical consulting, project definition
services, and project management support
2. Prepare pre-design and bridging documents
3. Utilize Port crews, in support of the STS Renewal & Replacement project (CIP
#801377) at the Seattle-Tacoma International Airport (SEA).
The amount of this request is $9,000,000.
The total program cost will be determined by the PDD, and the project team will be
back at Commission prior to additional authorization.
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