AirTrain nearing West Field Road station in 2018
|Owner||San Francisco Airports Commission|
|Locale||San Francisco International Airport|
|Transit type||People mover, Airport rail link|
|Number of lines||2|
|Number of stations||9|
|Began operation||February 24, 2003|
|Operator(s)||San Francisco Airports Commission|
|Number of vehicles||38 Bombardier Innovia APM 100 people mover vehicles|
|System length||6 mi (10 km)|
AirTrain is a fully automated people mover at San Francisco International Airport (SFO) that opened on February 24, 2003. It operates 24 hours a day on two separate lines, covering a total of six miles (10 kilometres). The service is free of charge, funded by a $20 "airport fee" charged by rental car companies.
Lines and stations
AirTrain operates on two lines—Red Line and Blue Line—both of which run every 2½ minutes. The Red Line travels in a clockwise loop, beginning with Garage G station and ending with Garage A station, which takes about 9 minutes to complete. The Blue Line travels in a counterclockwise loop, serving the same stations in reverse order, and also proceeding to West Field Road and the Rental Car Center, which takes 19 minutes for a round trip.
Alternatively, passengers may walk around the terminal loop instead of riding AirTrain, which takes about 25 minutes by foot; however, passengers must ride AirTrain to access the Rental Car Center.
AirTrain does not provide access to SFO's long-term parking garage and lots; instead, passengers must take a free airport shuttle bus between the airport terminals and the long-term parking areas. The end of the track past the Rental Car Center station is only about six hundred yards away from the airport's long-term parking garage; an extension to the garage is expected to be in service in 2020.
|Garage A||Red Line
|International Terminal A||Red Line
|Terminal 1||Red Line
|Terminal 2||Red Line
|Terminal 3||Red Line
|International Terminal G||Red Line
|Garage G / BART||Red Line
|West Field Road||Blue Line|
|Rental Car Center||Blue Line||
The AirTrain stations at the International Terminal are located one level above ticketing, at both ends of the main hall. Stations at Terminals 1, 2, and 3 are located on level 5 of the domestic parking garage and can be accessed near security checkpoints B, D, and F.
The AirTrain system was built by Bombardier Transportation at a cost of US $430 million and is composed of 38 Innovia APM 100 cars coupled in trains of up to three cars. The APM 100 cars can also be found at airports in Tampa, Denver, Atlanta, Seattle-Tacoma, Houston, and Madrid. They are operated automatically under Bombardier's Cityflo 650 CBTC (communications-based train control) signalling technology, making it one of the first radio-based train control systems to enter service.
The entire AirTrain fleet is wheelchair accessible and allows rented baggage carts on board.
Future expansion and upgrades
Two additional stations for the AirTrain system are under construction. One new station, with a cost of $15 million, will accompany the new airport Hyatt hotel that is planned to open in 2019 and would serve both the Blue and Red Lines. An additional Lot DD station that is under construction will serve a long-term parking garage (Lot DD) and rental car center and would operate on the Blue Line only. 
Additionally, the Airport Development Plan from 2016 forecasts that ridership on the two lines will be over capacity in the future (42% and 87% over capacity on the Red and Blue Lines respectively) and recommends upgrades that would increase capacity. Specific upgrades include acquiring 30 additional AirTrain cars, upgrading existing stations to accommodate 4-car trains, and upgrading the maintenance facility to accommodate additional vehicles.
- Douglas Greenberg (April 19, 2012). "SFO rental car co's may be mischarging $20 fee". The San Francisco Chronicle.
- "AirTrain Alert". San Francisco International Airport. San Francisco International Airport. Retrieved 4 March 2019.
- "Bombardier Marks 15th Anniversary of Its World-First Radio-Based, Driverless Rail Control System". Bombardier Transporatation. MarketWired. 29 March 2018. Retrieved 22 January 2019.
- Sabatini, Joshua (December 2, 2015). "San Francisco selects Hyatt to manage airport hotel". San Francisco Examiner. Retrieved December 28, 2018.
- "AirTrain Extension & Improvements". San Francisco International Airport. Retrieved December 28, 2018.
- "SFO celebrates opening of new, long-term parking lot with a price drop - SFChronicle.com". www.sfchronicle.com. 2019-04-21. Retrieved 2019-05-10.
- Alternatives Development and Evaluation (PDF). Draft Final Airport Development Plan (Report). San Francisco International Airport. September 2016. Retrieved December 28, 2018.
- Recommended Airport Development Plan (PDF). Draft Final Airport Development Plan (Report). San Francisco International Airport. September 2016. Retrieved December 28, 2018.
- SFO AirTrain, San Francisco International Airport.