Airport

Trips to airports are generally outside the typical daily travel modeled with Daysim. In Soundcast, airport trips are estimated based on travel surveys and forecasts from Seattle-Tacoma International Airport. (In future modeling, Paine Field may need to be included, as commercial flights begin there soon.)

Trips to the airport are estimated using the following formula, based on surveys from New Jersey and North Carolina, and as applied in Minneapolis (via research by Fehr and Peers and Stantec):

- `Airport Trip Ends HBO (production zone) = 0.02112 * population`
- `Airport Trip Ends WBO (production zone) = 0.01486 * employment`

Control totals are used to match Sea-Tac's current and forecasted total visitors, as shown below and stored within the dictionary "airport_control_total" in emme_configuration.py:

Year	Sea-Tac Visitors
2014	101,838
2020	130,475
2025	149,027
2030	170,216
2035	189,617
2040	211,228

After set to the control totals, trips are divided in half to represent trips to and from the airport. Trips are then split by mode using shares from home-based other trips previously derived for external trips. These trips are further divided by time of day.