ATS - Airport Transit System (Within the airport)
Access within the airport complex can be accomplished using O'Hare's Airport Transit System (ATS), a 2.5 mi (4 km) long automated people mover system that operates 24 hours a day, connecting all four terminals and the remote parking lots.
It is a free of use system which just takes nine minutes to complete its trip.
Location
Generally speaking, Arrivals is located on the first level and Departures are on the second level of each terminal.