In public transport, a request stop, flag stop, or whistle stop is a stop or station at which buses or trains, respectively, stop only on request; that is, only if there are passengers or freight to be picked up or dropped off. In this way, stops with low passenger counts can be incorporated into a route without introducing unnecessary delay. Vehicles may also save fuel by continuing through a station when there is no need to stop.
"Flag stop" airline service was historically offered by several scheduled passenger air carriers in the past into destinations with low airline passenger demand. As an example, in its June 1, 1969, worldwide system timetable, Pan American World Airways (Pan Am) had this explanation: "Flag stop: A stop will be made and traffic will be accepted only when operating conditions permit, and provided request to stop is made sufficiently in advance."
