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. The appearance of request stops varies greatly. Many are clearly signed, but many others rely on local knowledge.