Methods, systems, and apparatus, including computer programs encoded on computer storage media, for determining travel information. One of the methods includes obtaining flight information for each of a plurality of users, the flight having a flight identifier and associated with a particular scheduled departure time and departure location based on the scheduled departure time, obtaining location information for user devices associated with each user of the plurality of users determining that the respective user devices associated with a first group of users of the plurality of users, has a location associated with the departure location determining that the respective mobile devices associated with users of the first group are no longer in communication a mobile network and using the respective times at which the user devices are determined to no longer be in communication with the mobile network along with the scheduled departure time to determine a departure time.
