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In public transport, a request stop or flag stop describes a stopping point at which trains or buses stop only on an as-need or request basis; that is, only if there are passengers to be picked up or dropped off. In this way, infrequently used stopping points can be served efficiently.
Trains save fuel by continuing through a station when there is no need to stop. There is not a significant saving on time, because trains going through a request stop need to slow down enough to be able to stop if there are passengers waiting.
Rail transport 
In rail transport, a request stop, flag stop or whistle stop describes a station at which trains stop only on an as-needed basis, that is, only if there are passengers to be picked up or dropped off. At request stops for which there are no passengers to be dropped off, trains need only slow in the vicinity of the platform — or, in some cases, pass it at speed — instead of coming to a complete stop at an empty platform. In this way, lightly used stations can remain open and be served efficiently, rather than be closed.
The methods by which trains are notified that there are passengers waiting to be picked up at a request stop vary by station and country:
United Kingdom 
In the United Kingdom, most request stop stations require that the guard be informed by passengers wishing to stop at the station and that passengers waiting to catch the train merely make themselves clearly visible to the driver as the train approaches at a speed slow enough to stop if necessary. In some cases the station platform is observable by railway staff either near the station (e.g. in the signal box at Kidwelly railway station) or at the station itself. In these latter cases the staff may inform the driver in advance so that there is no need for the train to slow down unnecessarily when no passengers are waiting.
United States 
On some lines served by Amtrak, flag stop stations require that passengers have a reservation to embark or disembark at the station. If there are no reservations for such a station, the train will generally pass at speed. Flag stops on Amtrak are rare as of 2010. Examples of flag stops include Tyrone and Latrobe in Pennsylvania, and Alderson and Thurmond in West Virginia.
On two of the Alaska Railroad routes, passengers may flag trains nearly any place along the route.
The South Shore Line in northern Indiana, has a few flag stops at Gary Airport, Beverly Shores, and Hudson Lake. At these stops, boarding passengers must press a button which activates a strobe light visible to the engineer of the train who will make the stop. Alighting passengers must notify the conductor at the previous stop.
The Ontario Northland Railway's Polar Bear Express from Cochrane to Moosonee is operated as a flag-stop route. There are some flag-stop points on Via Rail route; one example is the Sayabec railway station in Quebec. Via Rail also provides flag stop service to a number of communities along its Sudbury – White River train in Northern Ontario, the Montreal – Senneterre train and the Montreal – Jonquière train in Quebec as well as several of its lines in Western Canada, in addition, passengers on certain routes can disembark at any mile marker on 48 hour notice.
Hong Kong 
In Hong Kong, all intermediate stations along the Peak Tramway are request stops, except the termini on both ends.
Austria and Switzerland 
In Austria and Switzerland, request stops sometimes feature an electronic signal indicator that is operated by the passengers themselves. If a passenger wants the next train to stop, he usually must push a button on the platform changing the signal well before the station. Because these signals are usually well before the station, trains are able to pass at speed if no passenger is waiting. Passengers inside the trains wishing to disembark at a request stop notify the driver by pressing a button inside the train.
Czech Republic 
For many decades request stops did not exist in Czechoslovakia, but they were introduced by the former Czechoslovak State Railways (ČSD) with the 1991-1992 timetable. The sign "na znamení" (×) is assigned to stopping of separate rides in the timetable, not to the train stop itself. Initially the system was only used on one-car trains because the conductor could ask passengers personally about where they wanted to alight. With modern train units, the request regime is more automated. These trains are usually equipped with push buttons for the use of those who want to alight at the next stop, and an indicator showing a request has been made. Train stops have no request signalling equipment – passengers must ensure they are visible on the platform as a signal to stop the train. Request stops are only used on local (regional) slow train services, usually run by railcars or small diesel multiple units.
In some cities, such as Plzeň, Most and Litvínov, the tram system has some request stops. In Prague, traffic regulation ordered to stop to all trams including non-public rides, for traffic safety reasons. In 2013, Prague is testing its first pair of tram request stops at ČSAD Smíchov.
Bus transport 
In bus transport the term request stop is used in two ways:
- A fixed bus stop which is only serviced if passengers request it, in a manner similar to a train request stop.
- A "Hail and ride" section of the route where passengers can request the bus be stopped at any point.
United Kingdom 
In urban areas, some bus stops are mandatory (i.e., the bus always stops there) while others are request stops. At a stop with many routes, a mandatory stop removes the confusion for passengers when multiple buses arrive within proximity.
Passengers wishing to board the bus at a request stop do so by hailing it with an extended arm as it approaches. Passengers wishing to leave the bus indicate this by using the stop bell or buzzer. Outside of urban areas where there are fewer overlapping routes, it is common for almost all bus stops to be request stops.
Request stops and mandatory stops have different signs in London. Mandatory stops have the TfL roundel symbol in red on a white background with the text "Bus Stop", while request stops have it in white on a red background with the text "Request Stop". However, TfL have recently abolished the distinction, making all bus stops request stops, and are in the process of changing all signage to reflect this.
The second type of request stop is also used in the UK, although it is not very common. It is normally referred to as "Hail and Ride". Passengers signal the driver in the same way as for a fixed request stop anywhere along the route of the bus, regardless of whether there is a fixed stop.
North America 
The term request stop is used on bus networks to describe a stop to let off or pick up passengers that is not at a marked or designated bus stop. This is offered primarily in two different ways:
- "night request stop", where bus passengers can request the driver of an evening or night bus to drop them off or pick them up at a safe place. This is usually allowed to make users feel safer and more comfortable when using the bus.
- "flag stop", where bus passengers can request the driver to pick them up (usually by waving or "flagging" their hand at the driver, hence the term "flag stop") and drop them off at safe locations. This practice is usually applied to routes running through rural or suburban areas that would not be effectively served by the traditional practice of waiting at a designated stop.
Some bus companies may choose to adopt variations of the above two principal services. For example, in Portland and Metro Vancouver, people using TriMet or TransLink at night can ask a bus driver to drop them off, but can not flag or request a bus driver to pick them up, even if they are in a safe boarding area. In York Region, Ontario, Strathcona County, near Edmonton, Alberta, passengers can use a "dial-a-ride" service by dialing a dispatcher one hour in advance of their journey and telling the dispatcher their name and location. The dispatcher will then tell the next available bus to go to that location and will also tell the requesting person the next bus that will pick them up. The Toronto Transit Commission offers night request stops to female riders after sunset, and to all riders who express a dire need during the day.
In the state of Andhra Pradesh, APSRTC Request Stop is written on boards in some places. The buses will stop only if people raise their hands visible to the driver.
Hong Kong 
As in the United Kingdom, passengers wishing to board a bus at a bus stop do so by hailing it with an extended arm as it approaches. Passengers wishing to leave the bus indicate this by using the stop bell or buzzer. Almost all bus stops are request stops, except for a few bus stops along downsloping roads which are designated by a bus operator as a mandatory stop, where all buses of that operator have to stop.
In Taiwan, on most buses users are required to raise their hand and press a "drop off" button if they want to board or disembark, otherwise the bus will pass the station without stopping.
Czech Republic 
In Czechoslovakia and the Czech Republic, bus request stops ("na znamení" on the stop sign, "×" in timetables) have long been used on all types of transport – urban (including trolleybuses), regional and long-distance. In recent decades, such differentiation is used especially in urban and integrated suburban bus (and trolleybus) transport. At some stops, the request-stop function is limited to some period of the day or of the week (weekend, evening and night past 8 p.m. etc. – such stops have a different signs in timetables, e. g. "*", "#" etc.). In rural and regional transport, and in long-distance transport, most operators abandoned such distinctions because the operation is more informal and all stops are de facto request stops, although they are not labelled as such.
Buses have usually a request push button. Traditional rules are that 1× press means a request to alight at a request stop (use of the button at other stops was considered as misuse), a double press requests the exit of a pram, and multiple presses indicate an emergency stop request. In the newest vehicles, the signal button is integrated with door-control button, and pram and wheelchair users have a different push button.
Bus stops have no signalling equipment. According to traditional state legislation, passengers must give a signal to the driver by putting their hand up (some passengers even flourish their hand). Some operators, including all of the Prague Integrated Transport (PID) area, have amended that rule and don't require lifting of the hand – it is sufficient for the passenger to stand visibly on the platform.
Ferry stop 
Along some ferry routes in the fjords in Norway, some stops are equipped with a light that embarking passengers must switch on in order for the ferry to include the stop and pick them up.
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