San Francisco AirTrain

AirTrain was built in 2003 by Bombardier using APM100 rolling stock. The APM100, like many small systems, uses rubber tires with a center steering guide, and Wikipdia has a list of systems using this rolling stock, which are mostly at airports because of its small capacity. AirTrain currently runs 2-car consists but has been constructed to accommodate 3 cars when volume requires.

There are two AirTrain routes, which run around the terminals and to several parking garages and the rental car center. There is direct transfer to the BART at garage G (which the BART station is built into) and of course transfer to various shuttles. Plans are in place to extend the AirTrain to the long term parking, likely by 2018.

AirTrain control is based on the Bombardier FlexiBlok control system, apparently now called CitiFlo* 650 (yes, with the asterisk). This is a moving-block system that can be used in ATP or unattended driving mode. Communications is via spread-spectrum radio - trains report position via radio and then receive movement authority via radio.