AirTrain is a fully automated people mover at San Francisco International Airport (SFO). The system was built by Bombardier at a cost of US $430 million, and opened on February 24, 2003. The trains operate 24 hours a day on two separate lines, covering a total of six miles (10 kilometres).

The entire AirTrain fleet is wheelchair accessible and allows rented moving carts onboard. The system is composed of 38 Innovia APM 100 cars built by Bombardier of Montreal, Canada. People movers using Innovia APM 100 cars can also be found at Tampa, Denver, Atlanta, Seattle-Tacoma, Houston, and Madrid International Airports.

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.