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For other uses, see Switch: which one?.

This article primarily uses North Americanterminology. British and Commonwealthterms are given in parentheses.

A railroad switch, turnout or [set of]points is a mechanical installation enablingrailway trains to be guided from one track toanother at a railway junction.

The switch consists of the pair of linkedtapering rails, known as points (switch railsor point blades), lying between the divergingouter rails (the stock rails). These pointscan be moved laterally into one of twopositions to direct a train coming from thenarrow end toward the straight path or thediverging path. A train moving from thenarrow end toward the point blades (i.e. itmay go either left or right) is said to beexecuting a facing-point movement.

Unless the switch is locked, a train comingfrom either of the converging directs willpass through the points onto the narrowend, regardless of the position of the points,as the vehicle's wheels will force the pointsto move. Passage through a switch in thisdirection is known as a trailing-pointmovement.

A switch generally has a straight "through"track (such as the main-line) and a divergingroute. The handedness of the installation isdescribed by the side that the divergingtrack leaves. Right-hand switches have adiverging path to the right of the straighttrack, when coming from the narrow end and

a left-handedswitch has thediverging trackleaving to the

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A right-hand railroad switch with pointindicator pointing to right

Animated diagram of a right-hand railroad switch, rail track Adivides into two: track B (the straight track) and track C (thediverging track)

A railroad switch in motion atHong Kong's Ferry Pier LRTterminus in Tuen Mun

leaving to theopposite side.

A straight track isnot always present;for example, bothtracks may curve,one to the left andone to the right(such as for a WyeSwitch) or bothtracks may curve,with differing radii,in the samedirection.

Operation

A railroad car's wheels areguided along the tracks byconing of the wheels.[1] Only inextreme cases does it rely onthe flanges located on theinsides of the wheels. When thewheels reach the switch, thewheels are guided along theroute determined by which ofthe two points is connected tothe track facing the switch. Inthe illustration, if the left pointis connected, the left wheel willbe guided along the rail of thatpoint, and the train will divergeto the right. If the right point isconnected, the right wheel'sflange will be guided along therail of that point, and the train willcontinue along the straight track.Only one of the points may beconnected to the facing track atany time; the two points aremechanically locked together toensure that this is always thecase.

The operation of a railroadswitch. In this animation, thered track is the one travelledduring a facing-pointmovement. The switchmechanism, shown in black,may be operated remotelyusing an electric motor orhand-operated lever or from anearby ground frame.

case.

A mechanism is provided to movethe points from one position to theother (change the points).Historically, this would require alever to be moved by a humanoperator, and some switches arestill controlled this way. However,most are now operated by aremotely controlled electric motoror by pneumatic or hydraulicactuation.

In a trailing-point movement, thewheels will force the points to theproper position. This is sometimesknown as running through theswitch. If the points are rigidlyconnected to the switch controlmechanism, the controlmechanism's linkages may be bent,requiring repair before the switchis again usable. For this reason,switches are normally set to theproper position before performing atrailing-point movement.[2]

An example of a mechanism that would require repair after a run-through in the trailing direction is a clamp-lock. This mechanism ispopular in the UK, but the damage caused is common to most typesof switches. However, some switches are designed to be forced tothe proper position without damage. Examples include variableswitches, spring switches, and weighted switches.

High-speed operation

Generally, switches are designed to be safely traversed at lowspeed. However, it is possible to modify the simpler types of switchto allow trains to pass at high speed. More complicated switchsystems, such as double slips are restricted to low-speed operation.On European High Speed Lines, it is not uncommon to find switcheswhere a speed of 200 km/h (124.3 mph) or more is allowed.

The conventional way to increase turnout speeds is to lengthen theturnout and use a shallower frog angle. If the frog angle is soshallow that a fixed frog cannot support a train's wheels, aswingnose crossing (US: moveable point frog) will be used. Higherspeeds are possible without lengthening the turnout by usinguniformly curved rail and a very low entry angle.

An AREMA (American Railway Engineering and Maintenance of WayAssociation) design number 20 turnout has a diverging speed limit of45 miles per hour (72.4 km/h).[3][4]

Operation in cold conditions

In cold conditions, snow and icecan prevent the correct operationof switches. In the past, peoplewere employed by railway

Gas heating keeps a switchfree from snow and ice

A switch on the Listowel andBallybunion Railway, Ireland, in1912

were employed by railwaycompanies to keep the switchesclear by sweeping the snow away,and this is still used in somecountries, especially on minorlines. Some were provided with gastorches for melting ice. Morerecently, switches have hadheaters installed in the vicinity ofthe points so that the temperatureof the rails in these areas can bekept above freezing. The heaters may be powered by gas orelectricity. In cases where gas or electric heaters are unable to beused due to logistical or economical constraints anti-icingchemicals, such as Ice Free Switch®, can be applied to create abarrier between the metal surfaces of the switch and ice.

Tram and monorailsystems

The switch points of tram linesare often operated remotely bythe driver. Monorail systemshave special switches.

Roller coaster switches

Many roller coasters haveswitches for the siding, or evenfor a double station system, forexample in Disneyland ResortParis' Space Mountain and Big

Thunder Mountain coasters.

Regular rail can cross its own track because the gaps in the rails forwheel flanges are narrow, permitting the bladed design in thisarticle. Round pipe roller coaster rails and box beam monorail railsusually have wheels riding at angles other than on top. Theseadditional other angle wheels are a larger loading gauge, requiringbig gaps in the rail (structure gauge) where rails cross or meet.

There are three basic switch designs for roller coasters. Flexing,substituting and table rotating rails have all been used. Flexing theentire rail truss, fixed at one end, to point towards an alternatedestination requires manipulating a long segment of rail. Substitutinga segment requires placing two or more segments of rail on flatplate that is moved in its entirety to provide straight or curvedtrack.

Alternatively these substitutiontrack segments can be wrappedaround a rotating cylinder,creating a triangular truss or atwo sided plate. Rotating atable with a curved tracksegment in a Y junction is theless used third option. If thecurved track turns the cars 60degrees, and three rail linesmeet as three equally spaced

Substitution track switch for railat Chester Zoo

meet as three equally spacedspokes, 120 degrees apart,then the curved track sitting ona turn table can be rotated toconnect any two of the threerail lines at this junction, creating a triangle junction.

Classification

The divergence and length of a switch is determined by the angle ofthe frog (the point in the switch where two rails cross, see below)and the angle or curvature of the switch blades. The length andplacement of the other components are determined from this usingestablished formulas and standards. This divergence is measured asthe number of units of length for a single unit of separation.

In North America this is generally referred to as a switch's "number".For example, on a "number 12" switch, the rails are one unit apartat a distance of twelve units from the center of the frog. In theUnited Kingdom points and crossings using chaired bullhead railwould be referred to using a letter and number combination. Theletter would define the length (and hence the radius) of the switchblades and the number would define the angle of the crossing(frog). Thus an A7 turnout would be very short and likely only to befound in tight places like dockyards whereas an E12 would be foundas a fairly high speed turnout on a mainline.

Safety

The correct setting of points is fundamental to the safe running ofa railway. For example, an incorrectly set switch may result in twotrains being on the same track, potentially causing a collision.

Perhaps the greatest security challenge in railway operation ispreventing the tampering of manually-operable switches. Similar(non-fatal) wrecks near Newport News, Virginia on August 12, 1992and in Stewiacke, Nova Scotia on April 12, 2001 resulted fromswitches being thrown open in front of the trains by teenagesaboteurs. To prevent these incidents, most unused switches arelocked up.

The 1998 Eschede train disaster was one of the world's deadliesthigh-speed train accidents, resulting in over 100 deaths. Itoccurred when a wheel rim failed at 200 km/h (125 mph), partiallyderailing the car. The wheel rim went through the floor of thecarriage and was dragging on the ground. On arrival at the junctionit threw the switch, causing the rear wheels of the car to switchonto a track parallel to the track taken by the front wheels. Thecar was thereby thrown into and destroyed the piers supporting a300-tonne roadway overpass.

In 1980, 18 people died in the Buttevant Rail Disaster at Buttevant,Co. Cork in Ireland, when the Dublin-Cork express was derailed athigh speed after being inadvertently switched into a siding viaground frame operated points.

The Potters Bar rail crash at Potters Bar, Hertfordshire in the UnitedKingdom occurred in May 2002, when a switch sprang to a differentposition as a coach crossed it, a type of mishap called "splitting the

This detail of a switch shows thepair of tapered moveable railsknown as the switch points(switch rails or point blades)

position as a coach crossed it, a type of mishap called "splitting theswitch." The front wheels of a coach progressed along the straighttrack as intended, but the rear wheels slewed along the divergingtrack. This caused the whole coach to detach from the train andslew sideways across the platform ahead. Fortunately, themovement of the switch occurred beneath the final coach, so thatalthough 7 people were killed, the front coaches remained on thetracks. Poor maintenance of the points was found to be the primarycause of the crash.

The initial conclusion of the inquiry into the Grayrigg derailment ofFebruary 23, 2007 blames an incorrectly maintained set of points.

History

On early lines, vehicles were moved between tracks by means ofsliding rails. The switch as we know it was patented by Charles Foxin 1832.

Prior to the widespread availability of electricity, switches atheavily-traveled junctions were operated from a signal boxconstructed near the tracks through an elaborate system of rodsand levers. The levers were also used to control railway signals tocontrol the movement of trains over the points. Eventually,mechanical systems known as interlockings were introduced tomake sure that a signal could only be set to allow a train toproceed over points when it was safe to do so. On some low-trafficbranch lines, in self-contained marshalling yards, or on heritagerailways, switches may still be operated in this way.

Components

Points (point blades)

The points (switch rails or pointblades) are the movable railswhich guide the wheels towardseither the straight or thediverging track. They aretapered on most switches, buton stub switches they havesquare ends.

In the UK and Commonwealthcountries, the term pointsrefers to the entire mechanism,whereas in North America theterm refers only to the movablerails.

Frog (common crossing)

The frog, also known as thecommon crossing (or K-Rail inAustralian terminology), refersto the crossing point of tworails. This can be assembled outof several appropriately cut andbent pieces of rail or can be a

A one-piece cast frog. The shinyline crosses the rusty line. ThisNorth American "self-guardingcast manganese" frog withoutguard rails has raised flanges onthe frog, bearing on the face ofthe wheel as it passes throughthe frog.

The frog (left) and guard rail(right) of a switch

bent pieces of rail or can be asingle casting of manganesesteel. On lines with heavy usethe casting may be treatedwith explosive shock hardeningto increase service life.[5] Afrog forms part of a railroadswitch, and is also used in alevel junction (flat crossing).The frog is designed to ensurethe wheel crosses the gap inthe rail without "dropping" intothe gap; the wheel and railprofile ensures that the wheel isalways supported by at leastone rail. To ensure that thewheels follow the appropriateflangeway, a check-rail ("guardrail" North Americanterminology) is installed insidethe rail opposite the frog.

On lines with heavy and/orhigh-speed traffic, a swingnose

crossing (moveable point frog) may be used. As the name implies,there is a second mechanism located at the frog. This moves asmall portion of rail, to eliminate the gap in the rail that normallyoccurs at the frog. A separate switch machine is required tooperate the movable point frog switch.

This term "frog" is taken from shape of the device resembling aleaping frog with legs extended forward and to the rear of the body.

On dual-gauge switches, a special frog is used where the 3rd railcrosses the common rail. Denver and Rio Grande crews called this a"toad."

Guard rail (check rail)

A guard rail (check rail) is ashort piece of rail placedalongside the main (stock) railopposite the frog. These existto ensure that the wheelsfollow the appropriateflangeway through the frog andthat the train does not derail.Generally, there are two ofthese for each frog, one byeach outer rail. Guard rails arenot required with a "self-guarding cast manganese" frog,as the raised parts of the casting serve the same purpose. Thesefrogs are for low-speed use and are common in rail yards.

Switch motor

A switch motor (also known asa switch machine, point motor

The switch motor (in this casean electric motor) andassociated mechanism used tooperate this switch can be seento the right in the picture

The mechanism used at aswitch. The two points arelocked together with a barbetween them. This barcontinues to the lever on thenear side of the tracks which isused to throw the switch. This isan example of a low switchstand, used at locations wherethere is not sufficient clearancefor a tall switch stand. Thisparticular stand is designed to betrailed through by rolling stock,which will cause the points tobecome lined for the route thatthe wheels have passed through.It has a reflectorised target.

a switch machine, point motoror point machine) is an electric,hydraulic or pneumaticmechanism that aligns thepoints with one of the possibleroutes. The switch motor alsoincludes electrical contacts todetect that the switch hascompletely set and locked. Ifthe switch fails to do this,signals are kept at red. There isalso usually some kind ofmanual handle for operating theswitch in emergencies, such aspower failures.

Points lever

A points lever, ground throw,or switchstand is a lever andaccompanying linkages that areused to align the points of aswitch manually. This lever andits accompanying hardware isusually mounted to a pair oflong sleepers that extend fromthe switch at the points. Theyare often used in a place of aswitch motor on infrequentlyused switches. In some places,infrequently used points may beoperated from a ground frame.To prevent the tampering withof these switches by outsidemeans, these switches arelocked up when not in use.

Facing point lock

A facing point lock, FPL or pointlock is a device which, as thename implies, locks a set ofpoints in position, as well asproving that they are in thecorrect position. The "facingpoint" part of the name refers to the fact that they are to preventmovement of the points during facing moves, where a train couldpotentially split the points (end up going down both tracks) if thepoints were to move underneath the train - during trailing moves,the wheels of a train will force the points into the correct position ifthey attempt to move.

In the United Kingdom, FPLs were incredibly common from an earlydate, due to laws being passed which forced the provision of FPLsfor any routes travelled by passenger trains - it was, and still is,illegal for a passenger train to make a facing move over pointswithout them being locked, either by a point lock, or temporarilyclamped in one position or another.[6]

Joints

Joints are used where the moving points meet the fixed rails of theswitch. They allow the points to hinge easily between theirpositions. Originally the movable switch blades were connected tothe fixed closure rails with loose joints, but since steel rails aresomewhat flexible it is possible to make this join by thinning a shortsection of the rail itself. This can be called a heelless switch.

Straight and curved switches

Turnouts were originally built with straight switch blades, whichended at the pointed end with a sharp angle. These switches causea bump when the train traverses in the turnout direction.

The switch blades could be made with a curved point which meetsthe stockrail at a tangent, causing less of a bump, but thedisadvantage is that the metal at the point is thin and necessarilyweak.

A solution to these conflicting requirements was found in the 1920son the German Reichsbahn.

The first step was to have different rail profile for the stock railsand switch rails, with the switch rails being about 25mm less high,and stockier in the middle.

Point indicators

As it is difficult to see the lie of a switch from a distance, especiallyat night, European railways and their subsidiaries provide pointindicators which are often illuminated.

Components gallery

A swingnosecrossing. The pointof the V-shaped railis moved to align therail in theappropriate directionwhere the two railscross.

Several differentstyles of switchstand on display

A ground frame (atBristol Temple Meadsstation, UK) containsa few levers formanually operatingnearby points

A light industrial oryard track switchjointpoints are joined tothe closure rails bybolts through a "jointbar" or "fish plates"

Types of switches

Apart from the standard right-hand andleft-hand switches, switches commonlycome in various combinations of

A double switch, ordouble slip. The pointsare set to connect theupper left and lowerright tracks.

come in various combinations ofconfigurations.

Slip switches

Double sl ip

A double slip switch (double slip) is anarrow-angled diagonal flat crossing oftwo lines combined with four pairs ofpoints in such a way as to allow vehiclesto change from one straight track to theother, as well as going straight across. Atrain approaching the arrangement mayleave by either of the two tracks on theopposite side of the crossing. To reachthe third possible exit, the train mustchange tracks on the slip and thenreverse.

The arrangement gives the possibility of setting four routes, but thefour blades at each end of the crossing are often connected tomove in unison, so the crossing can be worked by just two levers orpoint motors. This gives the same functionality of two points placedend to end. The additional complexity of this type of switchrestricts it to locations where space is limited, such as stations.

In North America, the arrangement may also be called a doubleswitch, or more colloquially, a puzzle switch. The Great WesternRailway in the United Kingdom used the term double compoundpoints, and the switch is also known as a double compound inVictoria (Australia).

Single sl ip

A single slip switch works on the same principle as a double slip butprovides for only one switching possibility. Trains approaching onone of the two crossing tracks can either continue over thecrossing, or switch tracks to the other line. However, trains fromthe other track can only continue over the crossing, and cannotswitch tracks. This is normally used to allow access to sidings andimprove safety by avoiding having switch blades facing the usualdirection of traffic. To reach the sidings from what would be afacing direction, trains must continue over the crossing, thenreverse along the curved route (usually onto the other line of adouble track) and can then move forward over the crossing into thesiding.

Outside sl ip

An outside slip switch is similar to thedouble or single slip switches describedabove, except that the switch blades areoutside of the diamond instead of inside.An advantage over an inside slip switch isthat trains can pass the slips with higherspeeds. A disadvantage over an inside slipswitch is that they are longer and needmore space.

A double, outside slipin Heidelberg mainstation

A scissors crossover: twopairs of switches linking twotracks to each other in bothdirections

A double crossover on theWenhu Line of the TaipeiMetro system. Trains used toreverse here since the placeit located was the originalextremity of the line.

more space.

An outside slip switch can be so long thatits slips do not overlap at all, as in theexample pictured. In such a case a single,outside slip switch is the same as tworegular switches and a regular crossing.An outside, double slip switch is about thesame as a scissors crossover (see below),but with the disadvantages:

The two parallel tracks cannot be used at the same time;That the slips are not straight and thus have a limited speed;

Advantage:

The crossing can be passed at full speed.

By the disadvantages over both the double inside slip switch andthe scissors crossover, double outside slip switches are only usedin rare, specific cases.

Crossover

A crossover is a pair of switchesthat connects two parallel railtracks, allowing a train on onetrack to cross over to the other.Like the switches themselves,crossovers can be described aseither facing or trailing.

When two crossovers are presentin opposite directions, one afterthe other, the four-switchconfiguration is called a doublecrossover. If the crossoversoverlap it is dubbed a scissorscrossover, scissors crossing, orjust scissors; or, due to thediamond in the center, a diamondcrossover. This makes for a verycompact track layout at theexpense of using a level junction.

In a setup where each of the twotracks normally carries trains ofonly one direction, a crossover canbe used either to detour "wrong-rail" around an obstruction or toreverse direction. A crossover canalso join two tracks of the samedirection, possibly a pair of localand express tracks, and allowtrains to switch from one to theother.

On a crowded system, routine useof crossovers (or switches ingeneral) will reduce throughput, asthe switches must be changed for

Überleitstelle (crossover) atRichthof between Kirchheim andLangenschwarz stations on theHanover–Würzburg high-speedrailway

A narrow gauge stubswitch

the switches must be changed foreach train. For this reason, on some high-capacity rapid transitsystems, crossovers between local and express tracks are not usedduring normal rush hour service, and service patterns are plannedaround use of the usually flying junctions at each end of the local-express line.

In Germany a crossover isknown as an Überleitstelle(abbreviated to: Üst) and isdefined as an operating controlpoint on the open line.[7] It isalso a block section. At anÜberleitstelle trains can transferfrom one track of a single ordouble track section of route toanother track on a double tracksection on the same route.Depending on the safetyequipment provided, trains mayrun this other track either byexception or routinely againstthe normal direction of traffic.

An Überleitstelle must have atleast one turnout. On double

tracked routes, single and double crossovers are common, each oneconsisting of two turnouts and an intermediate section. Very often- but not mandatory - the turnouts and block signals at anÜberleitstelle are remotely controlled or set from a central signalbox.

The official categorisation of an Überleitstelle as a type of junctionfirst arose in Germany with the construction of high-speed railways.Previous to that there were already operating control points atwhich trains could just transfer from one track to another on thesame route, but they were considered as junctions (Abzweigstelle).The latter are still used to refer to those places in stations whichenable trains to cross from one route to another.

Stub switch

A stub switch lacks the tapered points(point blades) of a typical switch.Instead, both the movable rails and theends of the rails of the diverging routeshave their ends cut off square. Theswitch mechanism aligns the movable railswith the rails of one of the divergingroutes. In 19th century US railroad use,the stub switch was typically used inconjunction with a harp switch stand.

The rails leading up to a stub switch are not secured to thesleepers for several feet, and rail alignment across the gap is notpositively enforced. Stub switches also require some flexibility in therails, or an extra joint at which they hinge. Therefore theseswitches cannot be traversed at high speed or by heavy traffic andso are not suitable for main line use. A further disadvantage is thata stub switch being approached from the diverging route that is notconnected by the points would result in a derailment. Yet another TopTopicsBuzz0

A narrow gauge plateswitch

A three-way stub switch atSheepscot station on theWiscasset, Waterville andFarmington Railway

connected by the points would result in a derailment. Yet anotherdisadvantage is that in very hot weather, expansion of the steel inthe rails can cause the movable rails to stick to the stock rails,making switching impossible until the rails have cooled andcontracted.

Stub switches were more common in the very early days of railwaysand their tramway predecessors. Now, because of theirdisadvantages, stub switches are used primarily on narrow gaugelines and branch lines. Some modern monorail switches use thesame principle.

Plate switch

A plate switch incorporates the taperedpoints of a typical switch into a self-contained plate. Each point blade ismoved separately by hand. Plate switchesare only used for double-flanged wheels,with wheels running through the plates ontheir flanges, guided by the edges of theplate and the moveable blade.

Because plate switches can only be usedby double-flanged wheels and atextremely low speeds, they are typicallyonly found on hand-worked narrow gaugelines.

Three-way switch

A three-way switch is used tosplit a railroad track into threedivergent paths rather than themore usual two. The complexityof such arrangements usuallyresults in severe speedrestrictions, and thereforethree-way switches are usuallyonly used in a station or depotwhere space is restricted andlow speeds are normal.

Stub switches can more readilyselect between three routes, somost three-way switches arestub switches, although somewere built using points.[8] Itwas extremely difficult to holdthe two rails the correctdistance apart for the length ofthe switch with these types of switch.

A three-way switch from aBrisbane tram depot is shownon the right. This example has

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A three-way switch formerly atBrisbane's Light Street tramdepot now on display at theBrisbane Tramway Museum

Chicago Transit Authority control tower 18 interlacedturnout

Interlaced turnouts on the elevated Chicago 'L' north andsouthbound Purple and Brown lines intersecting with eastand westbound Pink and Green lines and the looping Orangeline above the Wells and Lake street intersection in theloop.

on the right. This example hastwo points (point blades) oneach track, allowing for threediverging routes. The pointscan both be set to one side,resulting in a vehicle turning offthe straight track.Alternatively, the two bladescan be separated if the vehiclemust continue along thestraight track.

Interlaced turnout

An

interlaced turnout is a different method of splitting a track intothree divergent paths. It is an arrangement of two standardturnouts, one left- and one right-handed, in an "interlaced" fashion.The points of the second turnout are positioned between the pointsand the frog of the first turnout. In common with other forms ofthree way turnouts an additional common-crossing is required. Dueto the inherent complexity of the arrangement, interlaced turnoutsare normally only used in locations where space is exceptionallytight, such as station throats or industrial areas within large cities.Interlaced turnouts can also be found in some yards, where a seriesof switches branching off to the same side are placed so closetogether that the points of one switch are placed before the frog ofthe preceding switch.[9]

Wye switch

A wye switch (Y points) has trailing endswhich diverge symmetrically and inopposite directions. The name originatesfrom the similarity of their shape to thatof the letter Y. Wye switches are usuallyused where space is at a premium. InNorth America this is also called an

A wye switch

Trap points at the exitfrom a yard

North America this is also called an"Equilateral Switch" or "EquilateralTurnout".Common switches are more oftenassociated with mainline speeds, whereaswye switches are generally low-speedyard switches.

Run-off points

Main article: Catch points

Run-off points are used to protect mainlines from stray or runaway railroad carsor from trains passing signals set atdanger. In these cases, vehicles wouldotherwise roll onto and obstruct a mainline (sometimes known as fouling) andcause an accident. Depending on thesituation in which they are used, run-offpoints are referred to either as trap pointsor catch points. Derailers are anotherdevice used for the same purpose.

Catch points are installed on the running line itself, where therailway climbs at a steep gradient. They are used to preventrunaway vehicles colliding with another train further down theslope. In some cases, catch points lead into a sand drag to safelystop the runaway vehicle, which may be travelling at some speed.Catch points are usually held in the 'derail' position by a spring.They can be set to allow a train to pass safely in the downhilldirection using a lever or other mechanism to override the spring fora short time.

Catch points originate from the days of the 'unfitted' goods train.These trains did not have a mechanism in place to automaticallybrake runaway cars. Catch points were therefore required to stopthe rear portion of a train that had become divided, although theywould also stop vehicles that had run away for any other reason.Now that trains are all 'fitted', catch points are mostly obsolete.

Similar to catch points, trap points are provided at the exit from asiding or where a goods line joins a line that may be used bypassenger trains. Unless they have been specifically set to allowtraffic to pass onto the main line, the trap points will direct anyapproaching vehicle away from the main line. This may simply resultin the vehicle being derailed, but in some cases a sand drag is used,especially where the vehicle is likely to be a runaway travelling atspeed due to a slope.

Derailers

Main article: Derail

A derailer works by derailing any vehicle passing over it. There aredifferent types of derailer, but in some cases they consist of asingle switch point installed in a track. The point can be pulled intoa position to derail any equipment that is not supposed to pass.

Dual gauge switches

A dual gauge switch in Japan

Railroad switch on a rack railway(at Štrbské Pleso, Slovakia)

Dual gauge switches are used indual gauge systems. There arevarious possible scenarios involvingthe routes that trains on eachgauge may take, including the twogauges separating or one gaugebeing able to choose betweendiverging paths and the other not.Because of the extra trackinvolved, dual gauge switcheshave more points and frogs thantheir single gauge counterparts.This limits speeds even more thanusual.

A related formation is the 'swish' or rail exchange, where (usually)the common rail changes sides. These have no moving parts, thenarrower gauge wheels being guided by guard rails as theytransition from one rail to another. The wider gauge only encounterscontinuous rail so is unaffected by the exchange. At dual gaugeturntables, a similar arrangement is used to move the narrow gaugetrack from one side to a central position.

Rack railway switches

Rack railway switches are asvaried as rack railwaytechnologies. Where use of therack is optional, as on theZentralbahn in Switzerland orthe West Coast WildernessRailway in Tasmania, it iscommon to place turnouts onlyin relatively flat areas wherethe rack is not needed. Onsystems where only the pinionis driven and the conventionalrail wheels are idlers, such asthe Dolderbahn in Zurich,Štrbské Pleso in Slovakia andthe Schynige Platte rack railway, the rack must be continuousthrough the switch. The Dolderbahn switch works by bending allthree rails, an operation that is performed every trip as the twotrains pass in the middle. The Štrbské Pleso and Schynige PlatteStrub rack system instead relies on a complex set of moving pointswhich assemble the rack in the traversed direction andsimultaneously clear the crossed direction conventional rails. Insome rack systems, such as the Morgan system, where locomotivesalways have multiple driving pinions, it is possible to simplifyturnouts by interrupting the rack rail, so long as the interruption isshorter than the spacing between the drive pinions on thelocomotives.[10]

Switch diamond

Although not strictly speaking aturnout, a switch diamond is anactive trackwork assembly used

A switch diamond at ajunction in the UK

A single-point switch on theToronto streetcar system

active trackwork assembly usedwhere the crossing angle betweentwo tracks is too shallow fortotally passive trackwork- theunguided sections of each railwould overlap. These vaguelyresemble two standard pointsassembled very closely toe-to-toe.These would also often utiliseswingnose crossings at the outerends to ensure complete wheelsupport in the same way asprovided on shallow angleturnouts. In North America these are known as Movable-PointDiamonds. In the UK, where the angle of divergence is shallowerthan 1 in 8 (centre-line measure) a switched diamond will be foundrather than a passive or fixed diamond.

Such switches are usually implemented on the basis of increasingthe safe crossing speed. Open blades impose a speed restrictiondue to the potential of the crossing impact fracturing the rail.Remember that both wheels on an axle hit the crossing gaps almostsimultaneously. Switching the blades like the photo shows allows amuch higher speed across the gap.

The frog end is not as bad, because the outer rail is stillcontinuous, the wing rail (the bit that bends away after the froggap) provides a gradual transition, and the check rail avoids thepossibility of points splitting. Note how the wing rail has a widershiny section, showing how the wheel load is transferred across thegap.

Single-point switch

Single point switches, known asTongue and Plain Mateswitches, are sometimes usedon freight railways in slowspeed operation in paved areassuch as in ports. In the UnitedStates, they are regulated byprovision 213.135(i) of theFederal Railroad AdministrationTrack Safety Standards. Onstreetcar (tram) systems usinggrooved rails, if the wheels onboth sides of the car areconnected by a solid axle, onlyone switchpoint is needed to steer it onto one or the other track.The opposite wheel is supported for a short distance by its flangerunning in the groove.

Expansion joint

Expansion joints are a construction that allows the rails to moverelative to each other due to changes in temperature while retainingcontinuity for through traffic.[11] They are often used on largebridges such as the Sydney Harbour Bridge.

Turnout speeds

Turnout speeds are governed by a number of factors.

As a general rule, the finer the crossing angle of a turnout, thehigher the turnout speed. In USA, turnouts are rated by number,which represents the ratio of divergence per length as measured atthe frog. A rule of thumb is that the rated speed of a switch istwice the number.

#10 - 15 mph (24 km/h)#15 - 30 mph (48 km/h)#20 - 40 mph (64 km/h)

In Russia and CIS switches a marked with tangent of crossingangle.

1/6 - sorting yards only, whenever is impossible to install betterswitch1/9 - 40 km/h (25 mph), the most common switch, installed bydefault.1/11 - 50 km/h (31 mph), used where passenger trains followdiverging path. Swingnose crossing may be installed, if required.1/18 - 80 km/h (50 mph), used where either non-interruptiblemovement is required or mainline derives from branch line.1/22 - 120 km/h (75 mph), rarely used, hi-speed lines only.

Other considerations include the type of turnout (e.g. normal orswing nose, or slips etc.), wear and tear issues, and the weight andtype of the vehicle passing over. Speeds for a trailing movementmay be higher than for a facing movement. In many systems, speedlimits vary depending on the type of train - for example, a turnoutcan have a "normal" speed limit for locomotive hauled trains, and ahigher speed for multiple unit or high speed trains.

Turnouts with curved or tangential switch blades have higher speedthan old style turnouts with straight switch blades.

See also

Centralized traffic controlDouble junctionExpedition Everest, rollercoaster with switchesMinimum railway curveradiusRail terminology (US/UKdifferences highlighted)

Railway signalRailway signallingRailway switchingnetworksTurntable (rail)

References

1. ̂http://www.youtube.com/watch?v=y7h4OtFDnYE PhysicistRichard Feynman explains how a train stays on the tracks. BBCTV 'Fun to Imagine' (1983)

2. ̂Rules 8.9, 8.15, and 8.18, General Code of Operating Rules,Fifth Edition. (c) 2005 General Code of Operating Rules

Fifth Edition. (c) 2005 General Code of Operating RulesCommittee.

3. ̂Increasing speed through turnouts, from FindArticles.4. ̂A higher speed turnout, from Federal Railroad Administration,

US Department of Transportation.5. ̂Meyers, Marc A. (1994). Dynamic behavior of materials. New

York: John Wiley. pp. 5; 570. ISBN 9780471582625.6. ̂Requirements in regard to the Opening of Railways (1892),

from the British Board of Trade7. ̂§ 4, paragraph 6 of the Eisenbahn- Bau- und Betriebsordnung

or EBO (German Railway Regulations).8. ̂Stub switches9. ̂Example

10. ̂John H. Morgan, Switching or Crossover Device for TractionRack Rail Systems, U.S. Patent 772,736, Oct. 18, 1904.

11. ̂http://www.tokyu-car.co.jp/eng/rs/turnout.html

External links

PowerPoint presentation from Delft University of TechnologyJ. B. Calvert on Turnouts and the Wharton switch in particularMacPherson switchThyssenKrupp handbookPointworks industry and Research departmentsA video explaining how frogs work without resting on the flangetemplot Turnout design

Railway infrastructurePermanentway

Permanent way (history) • Permanent way (current) •Railroad tie/Sleeper • Rail fastening system • Trackballast • Rail profile • Fishplate • Breather switch •Datenail • Axe ties • Ladder track • Baulk road • Cant

Trackworkand trackstructures

Junction • Wye • Railroad switch • Gauntlet track •Railway electrification system • Overhead lines • Railgauge • Turntable • Water crane • Track pan

Signallingandsafety

Railway signalling • Signalling control • Railway signal •Interlocking • Level crossing • Buffer stop • Catchpoints • Loading gauge

Buildings Train station • Station building • Train shed •Classification yard • Goods shed • Motive power depot •Roundhouse

Railway track layoutsRunninglines

Single track • Passing loop • Double track • Quadrupletrack • Crossover

Railsidings

Balloon loop • Headshunt • Rail yard • Classification yard

Junctions Flying junction • Level junction • Double junction • Facingand trailing • Grand union • Wye • Switch / turnout /points • Swingnose crossing • Level crossing

Stations Side platform • Island platform • Bay platform • Splitplatform • Terminal station • Balloon loop • Spanishsolution • Cross-platform interchange

Hillclimbing Horseshoe curve • Zig Zag / Switchback • Spiral

Some text and images from Railroad switch at Wikipedia under the C reative CommonsA ttribution-ShareA like Licens e. 106680 bytes , 2011 -01-26

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