Editing Railroad switch (section)

== Operation ==
[[File:Railroad switch animation.gif|thumb|upright=1.2|The operation of a railroad switch. In this [[animation]], the red track is the one traveled during a facing-point movement. The switch mechanism, shown in black, may be operated remotely using an [[electric motor]] or hand-operated lever or from a nearby [[ground frame]].]]

A [[railroad car]]'s [[wheel]]s normally take up a position over the center of the rails by virtue of the [[wheel tread]]s' coning;<ref>{{Cite AV media |people=Richard Feynman |url=https://www.youtube.com/watch?v=y7h4OtFDnYE |title=Feynman: How the Train Stays on the Track |date=1983 |work=Fun to Imagine |publisher=BBC TV |via=YouTube.com }}</ref> the [[flange]]s on the inside edges of the wheels. When the wheels reach the switch, the wheels are guided along the route determined by which of the two points is connected to the track facing the switch. In the illustration, if the left point is connected, the left wheel will be guided along the rail of that point, and the train will diverge to the right. If the right point is connected, the right wheel will be guided along the rail of that point, and the train will continue along the straight track. Only one of the points may be connected to the facing track at any time; the two points are mechanically locked together to ensure that this is always the case.

A mechanism is provided to move the points from one position to the other ("changing the switch-blades" or "changing the points"). Historically, this would require a lever to be moved by a human operator, and some switches are still controlled this way. However, most are now operated by a remotely controlled actuator called a switch machine or [[point machine]], which may contain an [[electric motor]] or a [[Pneumatics|pneumatic]] or [[Hydraulic machinery|hydraulic]] [[actuator]]. This both allows remote control and monitoring, and the use of stiffer, strong switches that would be too difficult to move by hand.

In a trailing-point movement (running through the switch in the wrong direction while they are set to turn off the track), the flanges on the wheels will force the points to the proper position. This is sometimes known as ''running through the switch''. Some switches are designed to be forced to the proper position without damage. Examples include variable switches, spring switches, and weighted switches.

If the points are rigidly connected to the switch control mechanism, the control mechanism's linkages may be bent, requiring repair before the switch is again usable. For this reason, switches are normally set to the proper position before performing a trailing-point movement.<ref>{{cite book |author=General Code of Operating Rules Committee |date=2005 |title=General Code of Operating Rules |edition=Fifth |at=Rules 8.9, 8.15, and 8.18 }}</ref>

=== High-speed operation ===
Generally, switches are designed to be safely traversed at low speed. However, it is possible to modify the simpler types of switch to allow trains to pass at high speed. More complicated switch systems, such as double slips, are restricted to low-speed operation. On European high-speed lines, it is not uncommon to find switches where a speed of {{convert|200|km/h|0|abbr=on}} or more is allowed on the diverging branch. Switches were passed over at a speed of {{convert|560|km/h|0|abbr=on}} (straight) during the French world speed run of April 2007.<ref>{{cite web |url=https://extranet.artc.com.au/docs/eng/track-civil/procedures/pc/Section3.pdf?28 |website=Extranet.ARTC.com.au |archive-url=https://web.archive.org/web/20180327043114/https://extranet.artc.com.au/docs/eng/track-civil/procedures/pc/Section3.pdf?28 |title=Points and Crossings |archive-date=27 March 2018 |access-date=25 September 2022 }}</ref>

The US [[Federal Railroad Administration]] has published the speed limits for higher-speed turnouts with {{abbr|No.|Number}}&nbsp;26.5 turnout that has speed limit of {{cvt|60|mph|0}} and {{abbr|No.|Number}}&nbsp;32.7 with speed limit of {{cvt|80|mph|0}}.<ref name="63 FR 39343">{{cite web |title=63 FR 39343 – Automatic Train Control and Advanced Civil Speed Enforcement System; Northeast Corridor Railroads |url=http://www.gpo.gov/fdsys/granule/FR-1998-07-22/98-19431/content-detail.html |publisher=Federal Railroad Administration |access-date=21 October 2012 }}</ref>

=== Operation in cold conditions <span class="anchor" id="Cold conditions"></span>===
[[File:Weichenheizung.JPG|thumb|Gas heating keeps a switch free from snow and ice.]]
[[File:Rail Switch Heater.jpg|thumb|Similarly, an electric forced-air heater can keep a switch free from snow and ice.]]

Under cold weather conditions, snow and ice can prevent the proper movement of switch or [[#Frog|frog]] point rails, essentially inhibiting the proper operation of railroad switches. Historically, railway companies have employees keep their railroad switches clear of snow and ice by sweeping the snow away using switch brooms (Basically wire brooms with a chisel attached onto the opposite end of the broom – quite similar to ice scrapers used today), or gas torches for melting ice and snow. Such operation are still used in some countries, especially for branch routes with only limited traffic (e.g. seasonal lines). Modern switches for heavily trafficked lines are typically equipped with switch heaters installed in the vicinity of their point rails so that the point rails will not be frozen onto the stock rail and can no longer move. These heaters may take the form of electric heating elements or gas burners mounted on the rail, a lineside burner blowing hot air through ducts, or other innovative methods (e.g. geothermal heat sink, etc.) to keep the point & stock rails above freezing temperatures. Where gas or electric heaters cannot be used due to logistic or economic constraints, anti-icing chemicals can sometimes be applied to create a barrier between the metal surfaces to prevent ice from forming between them (i.e. having frozen together by ice). Such approaches however, may not always be effective for extreme climates since these chemicals will be washed away over time, especially for heavily thrown switches that experience hundreds of throws daily.{{Citation needed|date=March 2025}}

Heating alone may not always be enough to keep switches functioning under snowy conditions. Wet snow conditions, which generate particularly sticky snow and whiteout conditions, may occur at temperatures just below freezing, causing chunks of ice to accumulate on trains. When trains traverse over some switches, the shock, vibration, possibly in combination with slight heating caused by braking or a city microclimate, may cause the chunks of ice to fall off, jamming the switches. The heaters need time to melt the ice, so if service frequency is extremely high, there may not be enough time for the ice to melt before the next train arrives, which will then result in service disruptions. Possible solutions include installing higher capacity heaters, reducing the frequency of trains, or applying anti-icing chemicals such as [[ethylene glycol]] to the trains.<ref>{{cite web |url=http://www.prorail.nl/reizigers/weersinvloeden/winter |title=Information on Winter Operation by Dutch Infrastructure Manager Prorail |language=dutch |website=Prorail.nl |access-date=30 June 2024 }}</ref>