The estimated time of arrival or ETA (sometimes called ETOA) is a measure of when a ship, vehicle, aircraft, cargo, emergency service or computer file is expected to arrive at a certain place. One of the more common uses is in public transportation where the movements of trains, buses, airplanes and the like can be used to generate estimated times of arrival depending on either a static timetable or through measurements on traffic intensity. In this respect, the phrase or its abbreviation is often paired with its complement, "estimated time of departure" or "ETD", to indicate the expected start time of a particular journey. This information is often conveyed to a passenger information system as part of the core functionality of intelligent transportation systems.