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Automation, Controls

Case study: Streamlining Sea-Tac Airport via passenger simulation

Using complex simulation and modeling techniques, designers were able to understand the flow of passengers through the future international arrivals facility at Seattle-Tacoma International Airport

By Najim Afzalzada and Aarshabh Misra April 30, 2020
Courtesy: SOM

Learning objectives

  • Learn how advanced simulation and modeling are being applied to complex infrastructure projects to help enhance design.
  • Understand the benefits of using simulation and modeling tools to inform the decision-making process.
  • Know the importance of having good data and stakeholder consultation/communication.

As part of the Skidmore, Owings & Merrill architects and Clark Construction Group team, Arup has been involved in the progressive design-build delivery of Seattle-Tacoma International Airport’s new international arrivals facility since mid-2015. Arup has provided expertise across the breadth of the facility’s development, including aviation planning, passenger flow modeling, security, airport information systems, terminalwide voice paging, acoustic consulting and mechanical, electrical and plumbing engineering.

Facing the challenges of the most complex capital development program in the history of the 70-year-old airport, Arup’s experience at major airports around the globe helped to shape the design for the facility. Arup has been deeply involved in testing and validating passenger flow patterns and capacities through analysis of the facility and expected passenger processing rates for new U.S. Customs and Border Protection practices.

Figure 1: The Seattle-Tacoma International Airport’s new international arrivals facility is being built at the main terminal building with a connector to the south satellite building. The new facility will contain more than 450,000 square feet of space to accommodate the increase in international traffic at the airport. Courtesy: SOM

Figure 1: The Seattle-Tacoma International Airport’s new international arrivals facility is being built at the main terminal building with a connector to the south satellite building. The new facility will contain more than 450,000 square feet of space to accommodate the increase in international traffic at the airport. Courtesy: SOM

Sea-Tac is the eighth busiest airport in the United States, serving more than 50 million passengers annually. The airport serves as an important gateway into the West Coast for passengers and cargo alike and is one of the fastest growing airports in the country. The airport was built during World War II and expanded over multiple phases in the latter half of the 20th century to comprise four concourses in the main terminal and two satellite building facilities connected by an underground automated people mover.

Currently, passengers arriving from international destinations clear immigration and customs at the basement level of the south satellite in a facility that is 70% over its peak hour capacity of 1,200 passengers. Often during busy periods, passengers have to wait in the arrivals corridor due to overcrowding and lack of processing capacity at immigration, resulting in a poor experience.

To support the rapid increase in international traffic at the airport, in 2015 the Port of Seattle engaged with CBP and other stakeholders to develop a large-scale 450,000-square-foot IAF with an aerial walkway spanning 900 linear feet across and 85 feet above an existing aircraft taxi lane connecting the south satellite building to concourse A.

The design team used Simio, a discrete-event simulation modeling software, in conjunction with Oasys MassMotion, an advanced agent-based passenger simulation modeling software, to model the flow of passengers through the airside connector and the IAF to understand the area requirements for processing people at immigration and baggage claim. Simulation experts are typically involved during the early stages of the development to determine facility requirements before the development of the spatial/physical layout plans.

Future calculations

Simulations allow engineers to evaluate passenger level of service, including wait times, queue lengths and space available per passenger, to predict future demand levels. The primary input into simulation is the passenger demand, i.e., the number of people expected to use the facility in the future. For Sea-Tac, the passenger demand was based on forecast flight schedules representing demand levels corresponding to 20 years in the future.

Figure 2: An 85-foot-high bridge will connect international gates on the south satellite to the international arrivals facility over an active taxiway. The bridge is being designed to allow movement of jumbo jets under the bridge. Courtesy: SOM

Figure 2: An 85-foot-high bridge will connect international gates on the south satellite to the international arrivals facility over an active taxiway. The bridge is being designed to allow movement of jumbo jets under the bridge. Courtesy: SOM

Since the Port of Seattle’s calculation of future flight schedules in 2015, Seattle has seen exponential growth in the international market. To accurately represent future conditions at the IAF, various parameters such as passengers by type of origin/destination, passenger processing capacity of the immigration system and aircraft gate allocation were input into the simulation model (see Table 1).

Table 1: The flight schedule corresponding to these values forms the primary input into the simulation model. Courtesy: Arup/Port of Seattle

Table 1: The flight schedule corresponding to these values forms the primary input into the simulation model. Courtesy: Arup/Port of Seattle

At the outset of the project, three primary project goals were established for international arrival passengers:

  • Optimum level of service: The quality of the experience perceived by the passengers including space provisions and wait times, per International Air Transport Association’s “Airport Development Reference Manual.” Minimum connect time: The amount of transfer time for passengers to connect between an arriving international flight to a departing flight, with a target to decrease from current 90 minutes to 75 minutes.
  • International arrivals time in system: The amount of time passengers spend from deplaning the aircraft to the exit of primary processing at immigration, with a target of 60 minutes.

In 2015, the planning for IAF passenger flow was based on all international arriving passengers clearing immigration in two-steps of processing — first at an automated passport control kiosk and after picking up checked luggage from the reclaim carousels, speaking with a CBP document verification officer (see Figure 3).

Figure 3: A flow diagram of two-step automated passport control-based immigration process is simulated in Simio and Oasys MassMotion. Courtesy: Port of Seattle/CBP/Arup

Figure 3: A flow diagram of two-step automated passport control-based immigration process is simulated in Simio and Oasys MassMotion. Courtesy: Port of Seattle/CBP/Arup

Some passengers are also referred to a secondary process where CBP officers spend more time interviewing them in a segregated room outside the main arrivals hall. The simulation results showed that the peak demand of the long-term schedule could be accommodated by installing close to 100 APC kiosks and providing 40 CBP DVOs after baggage claim.

However, toward the end of 2017, CBP revised its policy to adopt a biometrics-based facial recognition technology for all new CBP facilities at airports across the United States — APC kiosks would no longer be supported or further developed. For Sea-Tac IAF, this meant that the facility now had to be modified to support a new technology and corresponding infrastructure. The new CBP strategy involved a simplified arrivals process where all passengers claim their bags before any interaction with CBP. This allowed passengers to have a single touch point with CBP in their journey (see Figure 4).

Figure 4: This flow diagram shows a single-step biometrics-based immigration process simulated in Simio and Oasys MassMotion. Courtesy: Port of Seattle/CBP/Arup

Figure 4: This flow diagram shows a single-step biometrics-based immigration process simulated in Simio and Oasys MassMotion. Courtesy: Port of Seattle/CBP/Arup

The biometrics-based process with no APCs was tested in the simulation models to understand impacts on the facility. The models quickly flagged inadequate vertical circulation capacity from the mezzanine to the bag claim level. Within the initial design, two escalators leading to the bag claim hall were sufficient, whereas in the absence of APCs, three escalators were needed to ensure adequate capacity. When the APCs were included on the mezzanine level, they metered the flow of passengers to the escalators.

Figure 5: An Oasys MassMotion agent-based passenger simulation model is shown for the international arrivals facility. Passenger flow is modeled with full collision avoidance in a 3D environment, which allows testing impacts of various scenarios before implementation. Courtesy: Arup

Figure 5: An Oasys MassMotion agent-based passenger simulation model is shown for the international arrivals facility. Passenger flow is modeled with full collision avoidance in a 3D environment, which allows testing impacts of various scenarios before implementation. Courtesy: Arup

Under the new approach, passengers would approach the escalator with no upstream process to moderate their flow. Consequently, passengers had a greater probability of accumulating around bag claim in larger numbers before checked bags reached the carousel because the overall passenger journey time to the carousels was reduced.

Technology updates

The change to facial recognition technology directly impacted the corresponding area requirements needed to support the new operation. Originally the passenger interface with CBP was split into two steps, self-service at APC followed by interaction with a CBP DVO; the processing time was split between the two processors, one of which was a machine (APC). With a biometrics-based approach, passengers have a single touch point with a CBP officer for processing. This results in an increase in the relative time spent with a CBP officer and, therefore, increases the number of officers required to handle the same passenger demand for a fixed wait time target.

The timeline to perform these analyses was tight because construction of the project was already underway — and sized for the original two-step passenger flow. However, the robust modeling framework facilitated efficient modifications to input data and allowed for rapid sensitivity testing and communication back to the design team.

Through trials performed at other airports, such as Atlanta; Orlando, Fla.; San Jose, Calif.; and San Diego, CBP provided data on passenger processing for the biometrics-based system. Based on this data and additional information available for current CBP operations at Sea-Tac, appropriate processing times were applied as distributed ranges in the simulation model to understand the corresponding impacts on passenger wait times and queues.

Several factors played a role when modeling such processes:

  • Passport split: People with U.S. and Canadian passports are usually prioritized over other nationalities as they have the lowest processing time relative to lawful permanent residents or nonimmigrants from a country that is not eligible for a visa waiver program.
  • Proximity of aircraft gate to IAF: Arrivals on gates in close proximity may result in localized passenger surges.
  • Passenger deboarding rate: Each gate has only a single bridge in contrast to some other airports that provide two bridges for larger aircraft to allow for faster deboarding of passengers.
  • Number of checked bags per passenger: This affects the amount of time passengers spend at the baggage reclaim carousel.

Understanding the nuances of an international arrivals process that has not been implemented is challenging. There are several aspects of the physical layout and the process itself that drive passenger behavior and, as a result, the processing performance of any facility. The processing times used in this study are unique to Sea-Tac’s current processes and passenger mix, so other airports should not expect similar results.

Table 2: This performance comparison is based on simulation results. Courtesy: Arup

Table 2: This performance comparison is based on simulation results. Courtesy: Arup

Careful planning

Numerous meetings were conducted with more than 20 stakeholders to expedite decision making and jointly develop a viable solution. The design team performed risk mitigation in the design layout through sensitivity testing; more than 50 different tests were performed by varying processing rates, CBP staffing levels and layouts in response to the queries raised during the meetings. Arup, SOM, Clark Construction and the Port of Seattle worked closely together to mitigate potential risks and convey significant outcomes to the various stakeholders.

Based on the sensitivities tested, three primary options emerged through stakeholder consultation. These reflected the most plausible solutions to improve operations and passenger experience.

  • Bags first: Arriving passengers pick up their checked bags from the carousel before speaking with a CBP officer. Simulation modeling demonstrated that this resulted in absence of any spare queuing capacity during periods of higher than normal surge activity.
  • CBP first: Arriving passengers speak to a CBP officer before picking up their checked bags from the carousel. In addition to not meeting the new CBP direction of retrieving bags first, this scenario resulted in no spare queuing capacity during periods of higher than normal surge activity.
  • Phased-in bags first: Arriving passengers are split based on their passport type between concourse A level and bag claim level. During peak periods, U.S. and Canadian passport holders follow a CBP first model using the space reserved for APCs on the concourse A level, while others follow a bags first model. During the off-peak, all passengers follow the bags first system. If facial recognition processing times decrease in the future, all passengers could use the bags first system regardless of peak periods or passport type.

Ultimately, CBP preferred a bags first model with a linear counter layout, which was aligned with CBP’s current operations and mitigated the risk of passengers trying to leave the area without being processed.

Throughout design development, the availability of an integrated simulation model provided common ground for all stakeholders and members of the design team to leverage data, constructively discuss issues and identify ways to resolve them. In the absence of a simulation model, analyzing and communicating the impact of the numerous design updates would have become very challenging.

Figure 6: Each passenger agent in the model is aware of their surroundings and their inherent characteristics. They follow an algorithm to perform various tasks such as collecting bags at claim devices or going through U.S. Customs and Border Protection, depending on these parameters. Immigration counters are shown with a linear layout. Courtesy: Arup

Figure 6: Each passenger agent in the model is aware of their surroundings and their inherent characteristics. They follow an algorithm to perform various tasks such as collecting bags at claim devices or going through U.S. Customs and Border Protection, depending on these parameters. Immigration counters are shown with a linear layout. Courtesy: Arup

This work also benefited greatly from involving stakeholders early in the project, which helped expedite decision-making. Through constant communication and stakeholder management, significant changes to the project were addressed in a timely fashion, often relying on quick turnaround of the simulation modeling results. With major construction underway and less than a year left to opening date, the design team was able to create a solution that delivers high-quality passenger experience and advances the Seattle area as a travel gateway.


Najim Afzalzada and Aarshabh Misra
Author Bio: Najim Afzalzada is an airport analyst in Arup’s Toronto office and has a particular expertise in airport capacity/demand analysis, future schedule development and passenger/baggage flow simulation. Aarshabh Misra is a senior airport analyst in Arup’s Toronto office. He is an expert in passenger simulation, modeling and analysis and works globally within the aviation industry.