![Bundesarchiv Bild 183-1985-0927-007, Dresden, Standseilbahn](https://upload.wikimedia.org/wikipedia/commons/0/08/Bundesarchiv_Bild_183-1985-0927-007%2C_Dresden%2C_Standseilbahn.jpg)
A railroad switch (), turnout, or
''set ofpoints () is a mechanical installation enabling
railway
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
trains to be guided from one
track to another, such as at a
railway junction
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. This implies a physical connection between the tracks of the two routes (assuming they are of the same gauge), provided by ''points'' ( ...
or where a
spur
A spur is a metal tool designed to be worn in pairs on the heels of riding boots for the purpose of directing a horse or other animal to move forward or laterally while riding. It is usually used to refine the riding aids (commands) and to ba ...
or
siding branches off.
The most common type of switch consists of a pair of linked tapering rails, known as ''points'' (''switch rails'' or ''point blades''), lying between the diverging outer rails (the ''stock rails''). These points can be moved laterally into one of two positions to direct a
train
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often ...
coming from the point blades toward the straight path or the diverging path. A train moving from the narrow end toward the point blades (i.e. it will be directed to one of the two paths, depending on the position of the points) is said to be executing a ''facing-point movement''.
For many types of switch, a train coming from either of the converging directions will pass through the switch regardless of the position of the points, as the vehicle's wheels will force the points to move. Passage through a switch in this direction is known as a ''trailing-point movement'' and switches that allow this type of movement are called ''trailable switches''.
A switch generally has a straight "through" track (such as the main-line) and a diverging route. The handedness of the installation is described by the side that the diverging track leaves. ''Right-hand switches'' have a diverging path to the right of the straight track, when coming from the point blades, and a ''left-handed switch'' has the diverging track leaving to the opposite side. In many cases, such as rail yards, many switches can be found in a short section of track, sometimes with switches going both to the right and left (although it is better to keep these separated as much as feasible). Sometimes a switch merely divides one track into two; at others, it serves as a connection between two or more parallel tracks, allowing a train to ''switch'' between them. In many cases, where a switch is supplied to leave a track, a second is supplied to allow the train to reenter the track some distance down the line; this allows the track to serve as a
siding, allowing a train to get off the track to allow traffic to pass (this siding can either be a dedicated short length of track, or formed from a section of a second, continuous, parallel line), and also allows trains coming from either direction to switch between lines; otherwise, the only way for a train coming from the opposite direction to use a switch would be to stop, and reverse through the switch onto the other line, and then continue forwards (or stop, if it is being used as a siding).
A ''straight track'' is not always present; for example, both tracks may curve, one to the left and one to the right (such as for a
wye switch), or both tracks may curve, with differing
radii
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
, while still in the same direction.
History
![PyinOoLwin23](https://upload.wikimedia.org/wikipedia/commons/f/f9/PyinOoLwin23.JPG)
Simple single-bladed switches were used on early wooden railways to move wagons between tracks. As iron-railed
plateway
A plateway is an early kind of railway, tramway or wagonway, where the rails are made from cast iron. They were mainly used for about 50 years up to 1830, though some continued later.
Plateways consisted of "L"-shaped rails, where the flange ...
s became more common in the eighteenth century, cast iron components were made to build switches with check rails. In 1797,
John Curr
John Curr (c. 1756 – 27 January 1823) was the manager or viewer of the Duke of Norfolk's collieries in Sheffield, England from 1781 to 1801. During this time he made a number of innovations that contributed significantly to the development of t ...
described the system that he developed which used a single iron blade, hinged on a vertical pin that was tapered to lie against the plateway. By 1808, Curr's basic design was in common use.
The switch was patented by
Charles Fox in 1832.
Prior to the widespread availability of
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...
, switches at heavily travelled
junctions were operated from a
signal box constructed near the tracks through an elaborate system of rods and
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...
s. The levers were also used to control
railway signal
A railway signal is a visual display device that conveys instructions or provides warning of instructions regarding the driver’s authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal mi ...
s to control the movement of trains over the points. Eventually, mechanical systems known as
interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively re ...
s were introduced to make sure that a signal could only be set to allow a train to proceed over points when it was safe to do so. Purely mechanical interlockings were eventually developed into integrated systems with electric control. On some low-traffic branch lines, in self-contained
marshalling yards, or on
heritage railways, switches may still have the earlier type of interlocking.
Operation
![Railroad switch animation](https://upload.wikimedia.org/wikipedia/commons/a/a8/Railroad_switch_animation.gif)
A
railroad car's
wheels are primarily guided along the tracks by
coning
Coning is a phenomenon which affects helicopter rotor discs. The tips of the helicopter rotor blades move faster through the air than the parts of the blades near the hub, so they generate more lift, which pushes the tips of the blades upward ...
of the wheels, rather than relying on the
flange
A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the f ...
s located on the insides 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's flange 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 (''change 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
point machine
A point machine (also known as a point motor, switch machine or switch motor) is a device for operating railway turnouts especially at a distance.
Overview
In the earliest times, points were operated manually by levers. Gradually, these were cen ...
; this may employ an
electric motor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
or a
pneumatic or
hydraulic
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
actuator. This both allows for remote control and monitoring and for the use of stiffer, strong switches that would be too difficult to move by hand, yet allow for higher speeds.
In a trailing-point movement (running through the switch in the wrong direction while they are set to turn off the track), the
flange
A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the f ...
s 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 a switch becomes worn or the operating rods become damaged, it is possible for the flange to ''split the switch'', and go through the switch in the direction other than what was expected. This happens when the flange strikes a small gap between the fixed rail and the set switch point (whichever is touching the main line); this forces the switch open, and the train is diverted down the incorrect track. This can either happen to the locomotive, in which case the whole train can be directed onto the wrong track, with potentially dangerous results, or it can occur at any point through the train, when a random truck is directed down a different track from the rest of the train; if this happens on the front truck of a car, the usual result is derailment, as the trailing truck of the preceding car attempts to go one way, while the leading truck of the following car tries to go another. If it happens to the trailing truck of a car, the front truck will follow one track, while the trailing truck follows a parallel line; this causes the whole car to "crab", or move sideways down the track (derailment often results eventually, due to the lateral forces applied when the train tries to brake or accelerate). This can have disastrous results if there is any obstacle between the lines, as the car will be propelled into it sideways, such as happened in the
1928 Times Square derailment
During the evening rush hour on August 24, 1928, an express subway train derailed immediately after leaving the Times Square station on the IRT Broadway–Seventh Avenue Line. Sixteen people were killed at the scene, two died later, and about 100 ...
. In some cases, the whole train behind the car will follow the errant car onto the other track; in others, only one or a few trucks are diverted, while the rest follow the correct track. In cases where it is a simple siding, rather than a continuous parallel track, the diverted truck(s) can travel the whole length of the siding until it turns back to the main track, where it performs a ''trailing point movement'', forces the switch open, and ends up back on the same track again, with only damage to the switches. This is far less likely in cases of diversion to a parallel track, since switches on both lines will often be interconnected, so to set the switch on the main line to straight-through will set the other switch to straight-through as well (otherwise there is a risk of turning off the track only to find the joining switch is set the wrong way, and running the train through it). Because derailments are expensive and very dangerous to life and limb, maintenance of switch points and other trackwork is essential, especially with faster trains. Another derailment that occurred due to a split switch is the
ProRail Hilversum derailment on 15 January 2014.
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.
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 or more is allowed on the diverging branch. Switches were passed over at a speed of (straight) during the French world speed run of April 2007.
The US
Federal Railroad Administration
The Federal Railroad Administration (FRA) is an agency in the United States Department of Transportation (DOT). The agency was created by the Department of Transportation Act of 1966. The purpose of the FRA is to promulgate and enforce rail saf ...
has published the speed limits for higher-speed turnouts with 26.5 turnout that has speed limit of and 32.7 with speed limit of .
Operation in cold conditions
![Rail Switch Heater](https://upload.wikimedia.org/wikipedia/commons/b/b6/Rail_Switch_Heater.jpg)
Under cold weather conditions, snow and ice can prevent the proper movement of switch or
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...
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.
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 like
ethylene glycol
Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
to the trains.
Classification
![Railroad Turnout on B&MLRR at City Point, ME](https://upload.wikimedia.org/wikipedia/commons/2/21/Railroad_Turnout_on_B%26MLRR_at_City_Point%2C_ME.jpg)
The divergence and length of a switch is determined by the angle of the frog (the point in the switch where two rails cross, see below) and the angle or curvature of the switch blades. The length and placement of the other components are determined from this using established formulas and standards. This divergence is measured as the 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 apart at a distance of twelve units from the center of the frog.
In the United Kingdom points and crossings using chaired bullhead rail would be referred to using a letter and number combination. The letter would define the length (and hence the radius) of the switch blades and the number would define the angle of the crossing (frog). Thus an A7 turnout would be very short and likely only to be found in tight places like dockyards whereas an E12 would be found as a fairly high speed turnout on a mainline.
On the
London, Midland and Scottish Railway, switch curvatures were specified from A (sharpest) to F (shallowest), with the following corresponding radii:
* B - - simple
crossover
Crossover may refer to:
Entertainment
Albums and songs
* ''Cross Over'' (Dan Peek album)
* ''Crossover'' (Dirty Rotten Imbeciles album), 1987
* ''Crossover'' (Intrigue album)
* ''Crossover'' (Hitomi Shimatani album)
* ''Crossover'' (Yoshino ...
with a 1 in 8
crossing angle
* C - - scissors or simple crossover with a 1 in 10 crossing angle
* D - -
double track junction switch with a 1 in 12 crossing angle
Safety
Switches are necessary for the operation of a railway, but they do pose a number of risks:
* Reversing the points under a moving train will almost always derail the train.
* Points might move due to the extreme forces exerted by a passing train. In an especially noteworthy and extreme case, a switch's setting was forcibly changed as a result of a disintegrated duo block wheel getting caught in a switch. This caused one of the world's worst rail disasters, the
Eschede train disaster
On 3 June 1998, an ICE 1 train derailed and crashed into an overpass that crossed the railroad, which then collapsed onto the train. The crash occurred on the Hannover-Hamburg railway near Eschede in Lower Saxony, Germany. In total, 101 peop ...
.
* A train might stand so close to the frog of a switch that a passing train would collide with its side (the first train is then said to have been ''fouling the switch'').
* The necessary maintenance of the complex mechanical device might be neglected.
* Tampering with a manually operable switch or operation errors in an
interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively re ...
may result in two trains being on the same track, potentially causing a collision.
To minimize accidents caused by these risks, suitable technical remedies as well as certain practices are applied. The most important are:
* Locks to prevent reversing a switch without a proper key.
* Interlockings that allow
signals
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
only to be cleared when switches are set correctly.
*
Track circuit
A track circuit is an electrical device used to prove the absence of a train on rail tracks to signallers and control relevant signals. An alternative to track circuits are axle counters.
Principles and operation
The basic principle behind t ...
s to prevent reversing when a passing train is detected.
*
Point locks or clamps that prevent movement of blades by locking them to the stock rails in a secure manner.
* Track circuits and fouling markers to point out fouling vehicles.
* Maintenance schedules, especially for measuring deviations of critical distances.
Accidents
Switch-related accidents caused by one or more of these risks have occurred, including:
* The 1980
Buttevant Rail Disaster at
Buttevant
Buttevant ( or ''Ecclesia Tumulorum'' in the Latin) is a medieval market town, incorporated by charter of Edward III, situated in North County Cork, Ireland.
While there may be reason to suggest that the town may occupy the site of an earlie ...
,
County Cork
County Cork ( ga, Contae Chorcaí) is the largest and the southernmost county of Ireland, named after the city of Cork, the state's second-largest city. It is in the province of Munster and the Southern Region. Its largest market towns a ...
, in Ireland, when the
Dublin
Dublin (; , or ) is the capital and largest city of Ireland. On a bay at the mouth of the River Liffey, it is in the province of Leinster, bordered on the south by the Dublin Mountains, a part of the Wicklow Mountains range. At the 2016 c ...
–
Cork
Cork or CORK may refer to:
Materials
* Cork (material), an impermeable buoyant plant product
** Cork (plug), a cylindrical or conical object used to seal a container
***Wine cork
Places Ireland
* Cork (city)
** Metropolitan Cork, also known as G ...
express was derailed at high speed after being inadvertently switched into a siding via
ground frame
Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals, track locks and points to allow the safe operation of trains in the area the signals control. Usually located in the signal box, th ...
operated points, resulting in 18 deaths.
* Wrecks caused by switches being thrown open in front of the trains by
saboteurs
Sabotage is a deliberate action aimed at weakening a polity, effort, or organization through subversion, obstruction, disruption, or destruction. One who engages in sabotage is a ''saboteur''. Saboteurs typically try to conceal their identiti ...
, as in the non-fatal derailments near
Newport News
Newport News () is an independent city in the U.S. state of Virginia. At the 2020 census, the population was 186,247. Located in the Hampton Roads region, it is the 5th most populous city in Virginia and 140th most populous city in the Uni ...
, on , and in
Stewiacke
Stewiacke () is a town located in southern Colchester County, Nova Scotia, Canada. The town was incorporated on August 30, 1906.
Geography
The town is located in the Stewiacke Valley, at the confluence of the Stewiacke and Shubenacadie Rive ...
, on . To prevent these incidents, most unused switches are locked up.
* The Eschede train disaster in 1998 in Germany was one of the world's deadliest high-speed train accidents, resulting in over 100 deaths. It occurred when a wheel rim failed at 200 km/h (125 mph), partially derailing the car. The wheel rim went through the floor of the carriage and was dragging on the ground. On arrival at the junction it threw the switch, causing the rear wheels of the car to switch onto a track parallel to the track taken by the front wheels. The car was thereby thrown into and destroyed the piers supporting a 300-tonne roadway overpass.
* The
May 2002 Potters Bar rail crash at
Potters Bar
Potters Bar is a town in Hertfordshire, England,in the historic County of Middlesex Hertsmere Borough Council – Community Strategy First Review (PDF) north of central London. In 2011, it had a population of 21,882. In 2022 the population was ...
,
Hertfordshire, in the United Kingdom, occurred when a switch sprang to a different position as a coach crossed it, a type of mishap called ''splitting the switch''. The front wheels of a coach progressed along the straight track as intended, but the rear wheels slewed along the diverging track. This caused the whole coach to detach from the train and slew sideways across the
platform
Platform may refer to:
Technology
* Computing platform, a framework on which applications may be run
* Platform game, a genre of video games
* Car platform, a set of components shared by several vehicle models
* Weapons platform, a system or ...
ahead. The movement of the switch occurred beneath the final coach, so that the preceding coaches remained on the track. Poor maintenance of the points was found to be the primary cause of the crash.
* The interim report into the
Grayrigg derailment
The Grayrigg derailment was a fatal railway accident that occurred at approximately 20:15 GMT on 23 February 2007, just to the south of Grayrigg, Cumbria, in the North West England region of the United Kingdom. The accident investigation conc ...
of blamed an incorrectly maintained set of points.
* Two fatal accidents involving the Amtrak
''Silver Star'' passenger train in South Carolina caused by switches either malfunctioning or misaligned.
** On July 31, 1991, several cars derailed killing 7 passengers, due to a missing locking pin on the switch mechanism.
** Twenty-seven years later, on August 4, 2018, the Silver Star
crashed into a parked freight train on a siding due to a misaligned switch, killing two crewmen.
Components
Points (point blades)
![Rail Turnout Switch Blades Old Style](https://upload.wikimedia.org/wikipedia/commons/4/41/Rail_Turnout_Switch_Blades_Old_Style.png)
The ''points'' (''switch rails'' or ''point blades'') are the movable rails which guide the wheels towards either the straight or the diverging track. They are tapered on most switches, but on ''stub switches'' they have square ends.
In the UK and Commonwealth countries, the term ''points'' refers to the entire mechanism, whereas in North America the term refers only to the movable rails.
In some cases, the switch blades can be heat treated for improvement of their service life. There are different kinds of heat treatment processes such as edge hardening or complete hardening.
The cross-section of the switch blades also influences performance. New tangential blades perform better than old-style blades.
(common crossing)
![Cast frog](https://upload.wikimedia.org/wikipedia/commons/2/2e/Cast_frog.jpg)
The frog, also known as the common crossing (or V-rail in Australian terminology), is the crossing point of two rails. This can be assembled out of several appropriately cut and bent pieces of rail or can be a single
casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
of manganese steel. On lines with heavy use the casting may be treated with
explosive shock hardening to increase service life.
On lines with heavy or high-speed traffic, a
swingnose crossing (movable-point frog) may be used. As the name implies, there is a second mechanism located at the frog. This moves a small portion of rail, to eliminate the gap in the rail that normally occurs at the frog. A separate switch machine is required to operate the movable-point frog switch.
This term ''frog'' is taken from the
part of a horse's hoof it most closely resembles. Certain types of
overhead electrification systems that make use of
trolley poles have similar devices referred to as wire frogs.
On dual-gauge switches, a special frog is used where the third rail crosses the common rail.
Denver and Rio Grande
The Denver & Rio Grande Western Railroad , often shortened to ''Rio Grande'', D&RG or D&RGW, formerly the Denver & Rio Grande Railroad, was an American Class I railroad company. The railroad started as a narrow-gauge line running south from De ...
crews called this a "toad".
A recent development on North American freight railroads is the
flange-bearing frog, in which the wheel flange supports the weight of the vehicle as opposed to the tread. This design reduces impact loading and extends the life of the frog.
Guard rail (check rail)
A ''guard rail'' (''check rail'') is a short piece of rail placed alongside the main (stock) rail opposite the frog. These ensure that the wheels follow the appropriate flangeway through the frog and that the train does not derail. Generally, there are two of these for each frog, one by each outer rail. Guard rails are not required with a "self-guarding cast manganese" frog, as the raised parts of the casting serve the same purpose.
''Check rails'' are often used on very sharp curves, even where there are no switches.
Switch motor
A ''switch motor'' (also known as a switch machine, point motor,
point machine
A point machine (also known as a point motor, switch machine or switch motor) is a device for operating railway turnouts especially at a distance.
Overview
In the earliest times, points were operated manually by levers. Gradually, these were cen ...
, or automater) is an
electric
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
,
hydraulic
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
or
pneumatic mechanism that aligns the points with one of the possible routes. The motor is usually controlled remotely by the dispatcher (signaller in the UK). The switch motor also includes electrical contacts to detect that the switch has completely set and locked. If the switch fails to do this, the governing signal is kept at red (stop). There is also usually some kind of manual handle for operating the switch in emergencies, such as power failures, or for maintenance purposes.
A patent by
W. B. Purvis dates from 1897.
Points lever
A ''points lever'', ''ground throw'', or ''switchstand'' is a
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...
and accompanying linkages that are used to align the points of a switch manually. This lever and its accompanying hardware is usually mounted to a pair of long
sleepers
''Sleepers'' is a 1996 American legal crime drama film written, produced, and directed by Barry Levinson, and based on Lorenzo Carcaterra's 1995 book of the same name. The film stars Kevin Bacon, Jason Patric, Brad Pitt, Robert De Niro, Dustin H ...
that extend from the switch at the points. They are often used in a place of a switch motor on infrequently used switches. In some places, the lever may be some distance from the points, as part of a
lever frame
Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals, track locks and points to allow the safe operation of trains in the area the signals control. Usually located in the signal box, the ...
or ground frame. To prevent the tampering of switches by outside means, these switches are locked up when not in use.
Point machine conversion
A point machine conversion system consist in a remotely controlled device attached to an existing manually operated point that allows the shunter or driver to remotely operate hand points with a radio handset. Each converter can be used as a stand-alone or multiple units can be installed operating together with routing.
Facing point lock
![Facing points Broomhill](https://upload.wikimedia.org/wikipedia/commons/3/3e/Facing_points_Broomhill.jpg)
A ''facing point lock'' (''FPL''), or ''point lock'', is a device which, as the name implies, locks a set of points in position, as well as mechanically proving that they are in the correct position. The ''facing point'' part of the name refers to the fact that they prevent movement of the points during facing moves, where a train could potentially ''split'' the points (end up going down both tracks) if the points were to move underneath the train. During trailing moves, the wheels of a train will force the points into the correct position if they attempt to move, although this may cause considerable damage. This act is known as a "run through".
In the United Kingdom, FPLs were common from an early date, due to laws being passed which forced the provision of FPLs for any routes traveled by passenger trains – it was, and still is, illegal for a passenger train to make a facing move over points without them being locked, either by a point lock, or temporarily clamped in one position or another.
Joints
''Joints'' are used where the moving points meet the fixed rails of the switch. They allow the points to hinge easily between their positions. Originally the movable switch blades were connected to the fixed closure rails with loose joints, but since steel is somewhat flexible it is possible to obviate this looseness by thinning a short section of the rail's bottom itself. This can be called a heelless switch.
Straight and curved switches
Turnouts were originally built with straight switch blades, which ended at the pointed end with a sharp angle. These switches cause a bump when the train traverses in the turnout direction. The switch blades could be made with a curved point which meets the stockrail at a tangent, causing less of a bump, but the disadvantage is that the metal at the point is thin and necessarily weak. A solution to these conflicting requirements was found in the 1920s on the German Reichsbahn. The first step was to have different
rail profile for the stock rails and switch rails, with the switch rails being about less high, and stockier in the middle.
Point indicators
As it is difficult to see the lie of a switch from a distance, especially at night, European railways and their subsidiaries provide
point indicators which are often illuminated.
Components gallery
Bewegliches Herzstueck.jpg , A swingnose crossing: The point of the V-shaped rail is moved to align the rail in the appropriate direction where the two rails cross.
Switch stands.jpg , Several different styles of old American switch stands on display at the Mid-Continent Railway Museum
The Mid-Continent Railway Museum is a railway museum, railroad museum in North Freedom, Wisconsin, North Freedom, Wisconsin, United States. The museum consists of static displays as well as a round trip ride aboard preserved railroad cars.
His ...
in North Freedom, Wisconsin
Groundframe.jpg , A ground frame contains a few levers for manually operating nearby points:
Blue lever: Release
Black lever: Points
Red lever: Signal
Switch joint.jpg, A light industrial or yard track switch joint, where the points are joined to the closure rails by bolts through a "joint bar" or "fish plates"
Aparelho de mudança de via do Transpraia.JPG , Railroad switch of a narrow gauge railway track
2-rail Funicular Railway 01.svg, Abt automatic turnout
File:QC-STM GarageBeaugrand 20040706-134131 AiguillageRaccordement.jpg, Switches on rubber-tyred metros use conventional points on the standard gauge track to guide trains. Rubber tires, rolling on concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
rollways, keep supporting the full weight of the trains as they go through switches. Guideways are provided in order to ensure there are no gaps in the electrical power supply.
Types
Apart from the standard right-hand and left-hand switches, switches commonly come in various combinations of configurations.
Slip switches
Double slip
![Double slip at Munich central](https://upload.wikimedia.org/wikipedia/commons/7/78/Double_slip_at_Munich_central.jpg)
A ''double slip switch'' (''double slip'') is a narrow-angled diagonal flat crossing of two lines combined with four pairs of points in such a way as to allow vehicles to change from one straight track to the other, alternatively to going straight across. A train approaching the arrangement may leave by either of the two tracks on the opposite side of the crossing. To reach the third possible exit, the train must change tracks on the slip and then reverse.
The arrangement gives the possibility of setting four routes, but because only one route can be traversed at a time, the four blades at each end of the crossing are often connected to move in unison, so the crossing can be worked by just two levers or point motors. This gives the same functionality of two points placed end to end. These compact (albeit complex) switches usually are found only in locations where space is limited, such as station throats (i.e. approaches) where a few main lines spread out to reach any of numerous platform tracks.
In North American English, the arrangement may also be called a ''double switch'', or more colloquially, a ''puzzle switch''. The
Great Western Railway in the United Kingdom used the term ''double compound points'', and the switch is also known as a ''double compound'' in
Victoria (Australia)
Victoria is a state in southeastern Australia. It is the second-smallest state with a land area of , the second most populated state (after New South Wales) with a population of over 6.5 million, and the most densely populated state in ...
. In Italian, the term for a double switch is , which means ''English switch''. Likewise, it is called in Dutch, and was called in German in former times.
Single slip
A ''single slip switch'' works on the same principle as a double slip, but provides for only one switching possibility. Trains approaching on one of the two crossing tracks can either continue over the crossing, or switch tracks to the other line. However, trains from the other track can only continue over the crossing, and cannot switch tracks. This is normally used to allow access to sidings and improve safety by avoiding having switch blades facing the usual direction of traffic. To reach the sidings from what would be a facing direction, trains must continue over the crossing, then reverse along the curved route (usually onto the other line of a double track) and can then move forward over the crossing into the siding.
Outside slip
![2001-07-19](https://upload.wikimedia.org/wikipedia/commons/7/7c/2001-07-19.0004.DKW-Baeseler.jpg)
An ''outside slip switch'' is similar to the double or single slip switches described above, except that the switch blades are outside of the diamond instead of inside. An advantage over an inside slip switch is that trains can pass the slips with higher speeds. A disadvantage over an inside slip switch is that they are longer and need more space.
An outside slip switch can be so long that its slips do not overlap at all, as in the example pictured. In such a case a single, outside slip switch is the same as two regular switches and a regular crossing. An outside, double slip switch is about the same as a ''scissors crossover'' (see below), but with the disadvantages:
* The two parallel tracks cannot be used at the same time.
* The slips are not straight and thus have a limited speed.
Advantage:
* The crossing can be passed at full speed.
Due to the disadvantages over both the ''double inside slip switch'' and the ''scissors crossover'', double outside slip switches are only used in rare, specific cases.
Crossover
![Scissors crossing Demachiyanagi](https://upload.wikimedia.org/wikipedia/commons/7/7e/Scissors_crossing_Demachiyanagi.JPG)
A ''crossover'' is a pair of switches that connects two parallel
rail tracks, allowing a train on one track to cross over to the other. Like the switches themselves, crossovers can be described as either ''facing'' or ''trailing''.
When two crossovers are present in opposite directions, one after the other, the four-switch configuration is called a ''double crossover''. If the crossovers in different directions overlap to form an ×, it is dubbed a ''scissors crossover'', ''scissors crossing'', or just ''scissors''; or, due to the diamond in the center, a ''diamond crossover''. This makes for a very compact track layout at the expense of using a
level junction
A level junction (or in the United Kingdom a flat crossing) is a railway junction that has a track configuration in which merging or crossing railroad lines provide track connections with each other that require trains to cross over in front o ...
.
In a setup where each of the two tracks normally carries trains of only one direction, a crossover can be used either to detour "wrong-rail" around an obstruction or to reverse direction. A crossover can also join two tracks of the same direction, possibly a pair of local and express tracks, and allow trains to switch from one to the other.
On a crowded system, routine use of crossovers (or switches in general) will reduce throughput, as use of the switch blocks multiple tracks. For this reason, on some high-capacity
rapid transit
Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be ...
systems, crossovers between local and express tracks are not used during normal
rush hour service, and service patterns are planned around use of the usually
flying junction
A flying junction or flyover is a railway junction at which one or more diverging or converging tracks in a multiple-track route cross other tracks on the route by bridge to avoid conflict with other train movements. A more technical term is " g ...
s at each end of the local-express line.
Stub switch
![Stub switch at Welsh Slate Museum](https://upload.wikimedia.org/wikipedia/commons/0/03/Stub_switch_at_Welsh_Slate_Museum.jpg)
A ''stub switch'' lacks the tapered points (point blades) of a typical switch. Instead, both the movable rails and the ends of the rails of the diverging routes have their ends cut off square. The switch mechanism aligns the movable rails with the rails of one of the diverging routes. In 19th century US railroad use, the stub switch was typically used in conjunction with a
harp switch stand.
The rails leading up to a stub switch are not secured to the
sleepers
''Sleepers'' is a 1996 American legal crime drama film written, produced, and directed by Barry Levinson, and based on Lorenzo Carcaterra's 1995 book of the same name. The film stars Kevin Bacon, Jason Patric, Brad Pitt, Robert De Niro, Dustin H ...
for several feet, and rail alignment across the gap is not positively enforced. Stub switches also require some
flexibility
Stiffness is the extent to which an object resists deformation in response to an applied force.
The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.
Calculations
The stiffness, k, of a bo ...
in the rails (meaning lighter rails), or an extra joint at which they hinge. Therefore, these switches cannot be traversed at high speed or by heavy traffic and so are not suitable for main line use. A further disadvantage is that a stub switch being approached from the diverging route that is not connected by the points would result in a derailment. Yet another disadvantage is that in very hot weather, expansion of the steel in the rails can cause the movable rails to stick to the stock rails, making switching impossible until the rails have cooled and contracted.
One advantage to stub switches is that they work better in the snow. The sideways action of the point rails pushes snow to the side, instead of packing the snow between the points and the rail in a more modern design.
Stub switches were more common in the very early days of railways and their tramway predecessors. Now, because of their disadvantages, stub switches are used primarily on
narrow gauge
A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and .
Since narrow-gauge railways are usually built with tighter curves, smaller structu ...
lines and
branch line
A branch line is a phrase used in railway terminology to denote a secondary railway line which branches off a more important through route, usually a main line. A very short branch line may be called a spur line.
Industrial spur
An industr ...
s. Some modern monorail switches use the same principle.
Three-way switch
![ThreeWayStub](https://upload.wikimedia.org/wikipedia/commons/3/3f/ThreeWayStub.jpg)
A ''three-way switch'' is used to split a railroad track into three divergent paths rather than the more usual two. There are two types of three-way switches. In a ''symmetrical three-way switch'', the left and right branches diverge at the same place. In an ''asymmetrical three-way switch'', the branches diverge in a staggered way. Both types of three-way switches require three frogs.
The complexity of symmetrical switches usually results in speed restrictions, therefore three-way switches are most often used in stations or depots where space is restricted and low speeds are normal. Symmetrical switches were used quite often on Swiss narrow-gauge railways. Asymmetrical three-way switches are more common, because they do not have speed restrictions compared to standard switches. However, because of their higher maintenance cost due to special parts as well as asymmetric wear, both types of three-way switches are replaced with two standard switches wherever possible.
In areas with very low speeds, like depots, and on railroads that had to be built very cheaply, like logging railroads, three-way switches were sometimes built as stub switches.
Plate switch
![Plate switch at Welsh Slate Museum](https://upload.wikimedia.org/wikipedia/commons/0/01/Plate_switch_at_Welsh_Slate_Museum.jpg)
A ''plate switch'' incorporates the tapered points of a typical switch into a self-contained plate. Each point blade is moved separately by hand. Plate switches are only used for double-flanged wheels, with wheels running through the plates on their flanges, guided by the edges of the plate and the moveable blade.
Because plate switches can only be used by double-flanged wheels and at extremely low speeds, they are typically only found on hand-worked narrow gauge lines.
Off-railer
The off-railer is a system of installing a turnout over and above some plain track, without having to cut or replace that track. It is useful for installing temporary branches on agricultural railways, and sidings for track machines on mainline rails. Special ramps lift the wheels off the normal track, and then the off-railer curves away as required. Decauville has such a system. It is a bit like a
drawbridge crossing.
Interlaced turnout
An ''interlaced turnout'' is a different method of splitting a track into three divergent paths. It is an arrangement of two standard turnouts, one left- and one right-handed, in an "interlaced" fashion. The points of the second turnout are positioned between the points and the frog of the first turnout. In common with other forms of three way turnouts an additional common-crossing is required. Due to the inherent complexity of the arrangement, interlaced turnouts are normally only used in locations where space is exceptionally tight, such as station throats or industrial areas within large cities. Interlaced turnouts can also be found in some yards, where a series of switches branching off to the same side are placed so close together that the points of one switch are placed before the frog of the preceding switch.
Wye switch
![Points near Ravenstein](https://upload.wikimedia.org/wikipedia/commons/5/5a/Points_near_Ravenstein.jpg)
A ''wye switch'' (''Y points'') has trailing ends which diverge symmetrically and in opposite directions. The name originates from the similarity of their shape to that of the letter Y. Wye switches are usually used where space is at a premium. In North America this is also called an "equilateral switch" or "equilateral turnout". Common switches are more often associated with mainline speeds, whereas wye switches are generally low-speed yard switches.
One advantage of wye switches is that they can have a coarser frog angle using the same radius of curvature than a common switch. This means that they give rise to a less severe speed restriction than the diverging branch of a common switch, without having to resort to more expensive switches with a moving frog. For this reason they are sometimes used on a main line where it splits into two equally important branches or at the ends of a single track section in an otherwise double track line.
Run-off points
![StokeGiffordYard-catchpoints](https://upload.wikimedia.org/wikipedia/commons/5/5e/StokeGiffordYard-catchpoints.jpg)
''Run-off points'' are used to protect main lines from stray or runaway cars, or from trains passing signals set at danger. In these cases, vehicles would otherwise roll onto and foul (obstruct) the main line and cause a collision. Depending on the situation in which they are used, run-off points are referred to either as trap points or catch points. Derailers are another device used for the same purpose.
''Catch points'' are installed on the running line itself, where the railway climbs at a steep gradient. They are used to prevent runaway vehicles colliding with another train further down the slope. In some cases, catch points lead into a sand drag to safely stop the runaway vehicle, which may be travelling at 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 downhill direction using a lever or other mechanism to override the spring for a short time.
Catch points originate from the days of the 'unfitted' goods (freight) train. As these trains tended to consist of either completely unbraked wagons (relying entirely on the locomotive's own brakes), or ones with unlinked, manually applied brakes (necessitating a stop at the top of steep downgrades for the guard to walk along the train and set the brakes on each wagon in turn), they also lacked any mechanism to automatically brake runaway cars. Catch points were therefore required to stop the rear portion of a poorly coupled train that might break away whilst ''climbing'' a steep grade – although they would also stop vehicles that ran away for any other reason. Now that trains are all 'fitted' (and broken couplings are far less common), catch points are mostly obsolete.
Similar to catch points, ''trap points'' are provided at the exit from a siding or where a goods line joins a line that may be used by passenger trains. Unless they have been specifically set to allow traffic to pass onto the main line, the trap points will direct any approaching vehicle away from the main line. This may simply result in the vehicle being derailed, but in some cases a sand drag is used, especially where the vehicle is likely to be a runaway travelling at speed due to a slope.
Derailers
A ''derailer'' works by derailing any vehicle passing over it. There are different types of derailers, but in some cases they consist of a single switch point installed in a track. The point can be pulled into a position to derail any equipment that is not supposed to pass through.
Dual gauge switches
![DualgaugeHakonetozanJP14](https://upload.wikimedia.org/wikipedia/commons/9/99/DualgaugeHakonetozanJP14.jpg)
''Dual gauge switches'' are used in
dual gauge systems. There are various possible scenarios involving the routes that trains on each gauge may take, including the two gauges separating or one gauge being able to choose between diverging paths and the other not. Because of the extra track involved, dual gauge switches have more points and frogs than their single gauge counterparts. This limits speeds even more than usual.
A related formation is the 'swish' or rail exchange, where (usually) the common rail changes sides. These have no moving parts, the narrower gauge wheels being guided by
guard rails
Guard rail, guardrails, or protective guarding, in general, are a boundary feature and may be a means to prevent or deter access to dangerous or off-limits areas while allowing light and visibility in a greater way than a fence. Common shapes ...
as they transition from one rail to another. The wider gauge only encounters continuous rail so is unaffected by the exchange. At dual gauge turntables, a similar arrangement is used to move the narrow gauge track from one side to a central position.
Rack railway switches
![Rack railway turnout (SPB)](https://upload.wikimedia.org/wikipedia/commons/e/ee/Rack_railway_turnout_%28SPB%29.JPG)
Rack railway switches are as varied as
rack railway
A rack railway (also rack-and-pinion railway, cog railway, or cogwheel railway) is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with th ...
technologies. Where use of the rack is optional, as on the
Zentralbahn
The Zentralbahn is a Switzerland, Swiss railway company that owns and operates two connecting railway lines in Central Switzerland and the Bernese Oberland. It was created on January 1, 2005, with the acquisition of the independently owned Luze ...
in Switzerland or the
West Coast Wilderness Railway
The West Coast Wilderness Railway is a reconstruction of the Mount Lyell Mining and Railway Company Mount Lyell railway in Western Tasmania between Queenstown and Regatta Point, Strahan. The railway is significant because of its Abt rack s ...
in
Tasmania
)
, nickname =
, image_map = Tasmania in Australia.svg
, map_caption = Location of Tasmania in AustraliaCoordinates:
, subdivision_type = Country
, subdi ...
, it is common to place turnouts only in relatively flat areas where the rack is not needed. On systems where only the pinion is driven and the conventional rail wheels are idlers, such as the
Dolderbahn
The Dolderbahn (Db or DBZ) is a long rack railway in the Swiss city of Zürich. The line is in Zürich's Hottingen and Fluntern suburbs on the south slope of the Adlisberg mountain. The lower terminus of the line is at ''Römerhof'', some ...
in
Zürich
, neighboring_municipalities = Adliswil, Dübendorf, Fällanden, Kilchberg, Maur, Oberengstringen, Opfikon, Regensdorf, Rümlang, Schlieren, Stallikon, Uitikon, Urdorf, Wallisellen, Zollikon
, twintowns = Kunming, San Francisco
Zürich ...
,
Štrbské Pleso
Štrbské pleso (, german: Tschirmer See, pl, Szczyrbskie jezioro, hu, Csorbató or ) is a picturesque mountain lake of glacial origin and a top tourist destination in the High Tatras, Slovakia. It is the second-largest glacial lake on the Sl ...
in
Slovakia
Slovakia (; sk, Slovensko ), officially the Slovak Republic ( sk, Slovenská republika, links=no ), is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the s ...
and the
Schynige Platte
The Schynige Platte (''Scheinige Platte'' on the old Siegfried Map) is a small mountain ridge and a viewpoint in the Bernese Highlands and belongs to the Schwarzhorn group. The mountain range consists of three peaks: Gumihorn (), Tuba (), and t ...
rack railway, the rack must be continuous through the switch. The Dolderbahn switch works by bending all three rails, an operation that is performed every trip as the two trains pass in the middle. The Štrbské Pleso and Schynige Platte Strub rack system instead relies on a complex set of moving points which assemble the rack in the traversed direction and simultaneously clear the crossed direction conventional rails. In some rack systems, such as the
Morgan system, where locomotives always have multiple driving pinions, it is possible to simplify turnouts by interrupting the rack rail, so long as the interruption is shorter than the spacing between the drive pinions on the locomotives.
Some systems use
transfer table
A transfer table or traverser is a piece of railway equipment. It functions similarly to a turntable, although it cannot be used to turn vehicles around.
Overview
A transfer table, also known as a traverser, consists of a single length of track th ...
s instead to provide continuous rack. The
Pilatus Railway
The Pilatus Railway (german: Pilatusbahn, links=no, PB) is a mountain railway in Switzerland and the steepest rack railway in the world, with a maximum gradient of 48% and an average gradient of 35%. The line runs from Alpnachstad, on Lake Al ...
has unusual switches that rotate on an axis parallel to the track.
Switch diamond
![Switchdiamond](https://upload.wikimedia.org/wikipedia/commons/f/f0/Switchdiamond.jpg)
Although not strictly speaking a turnout, a ''switch
diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
'' is an active trackwork assembly used where the crossing angle between two tracks is too shallow for totally passive trackwork: the unguided sections of each rail would overlap. These vaguely resemble two standard points assembled very closely toe-to-toe. These would also often utilise
swingnose crossings at the outer ends to ensure complete wheel support in the same way as provided on shallow angle turnouts. In North America these are known as ''Movable-Point Diamonds''. In the UK, where the angle of divergence is shallower than 1 in 8 (center-line measure) a switched diamond will be found rather than a passive or fixed diamond.
Such switches are usually implemented on the basis of increasing the safe crossing speed. Open blades impose a speed restriction, due to the potential of the crossing impact fracturing the rail as both wheels on each axle hit the crossing gaps almost simultaneously. Switched blades, as shown in the photograph, allow a much higher speed across the gap by providing an essentially continuous piece of rail across the gap on both sides.
The frog end of the switched crossing, despite still having a gap in one rail, is less problematic in this regard. The outer rail is still continuous, the wing rail (the part that turns out, after the frog gap) provides a gradual transition, and the check rail avoids the possibility of points splitting. This can be seen in how, under examination, the wing rail has a wider polished section, showing how the wheel load is transferred across the gap.
Single-point switch
![ON-TTC 20071110 StreetcarTrackSwitchPoint](https://upload.wikimedia.org/wikipedia/commons/1/14/ON-TTC_20071110_StreetcarTrackSwitchPoint.jpg)
Single point switches, known as Tongue and Plain Mate switches, are sometimes used on freight railways in slow speed operation in paved areas such as in ports. In the United States, they are regulated by provision 213.135(i) of the Federal Railroad Administration Track Safety Standards.
On streetcar (
tram
A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport are ...
) systems using
grooved rails, if the wheels on both sides of the car are connected by a rigid solid axle, only one switchpoint is needed to steer it onto one or the other track. The switchpoint will be on inside rail of the switch's curve route. When a streetcar enters the curve route of the switch, the wheel on the inside of the curve (the right side of the car on a right turn) is pulled into the turn, and through the axle, directs the wheel on the outside to also follow the curve.
[ The outside wheel is supported for a short distance by its flange running in the groove.
Some low floor streetcar designs use split axles (a separate half-axle for the wheel on each side of the car). Such streetcars are unsuitable for use with single-point switches as there would be no mechanism to transfer the force from the inner to outer wheels at switches.][
A single-point switch is cheaper to build, especially in street trackage, as there is no need to link to a second switchpoint.]
Rotary switch
Rotary switches are sometimes used on cog railways to maintain alignment of the cog with two different tracks. They are used on the Pilatus Cog Railway to allow up-bound and down-bound trains to pass each other on a grade while sharing the remainder of the single track.
A rotary switch rotates about its long axis to present a track connection to a chosen set of tracks. Physically, it flips over (rotates about its long axis 180 degrees) to connect to the chosen set of tracks. Once the rotary switch is secured the train can proceed. Cog alignment is maintained in both positions.
Temporary points
When a tram track is interrupted during repairs, a set of temporary points may be placed on top of existing track to allow trams to cross to the parallel track. These are known as ' or ''Auflegeweichen'' in German, ''aiguillages californiens'' in French, and ', ''klimwissels'' or ''Californische wissels'' in Dutch. They may be welded into place and allow trams to pass at walking pace.
Expansion joint
Expansion joint
An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...
s look like a part of a railroad switch, but have a completely different purpose, namely to compensate for the shrinkage or expansion of the road bed - e.g. typically, a larger steel bridge - due to changes in temperature, to avoid sun kink.
Turnout speeds
Turnout speeds are governed by a number of factors.
As a general rule, the smaller the crossing angle of a turnout, the higher the turnout speed.
In North America, turnouts are rated numerically, which represents the ratio of divergence per length as measured at the frog. A rule of thumb is that the rated speed of a switch (in miles per hour) is twice the numerical rating:
* 15:
* 20:
Higher speed turnouts have also been used in the United States:
* 26.5:
* 32.7:
In most other countries, switches are marked with tangent
In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. Mo ...
of crossing angle. For example, Russia and the rest of the Commonwealth of Independent States
The Commonwealth of Independent States (CIS) is a regional intergovernmental organization in Eurasia. It was formed following the dissolution of the Soviet Union in 1991. It covers an area of and has an estimated population of 239,796,010. ...
(CIS) use the following designations:
* 1/6: sorting yards only, whenever it is impossible to install a better switch
* 1/9: , the most common switch, installed by default
* 1/11: , used where passenger trains follow a diverging path. Swingnose crossing may be installed if required.
* 1/18: , used where either non-interruptible movement is required or the mainline diverges from the branch line
* 1/22: , rarely used, high-speed lines only
In Germany, Austria, Switzerland, Czech Republic, Poland and other European countries, switches are described by the radius of the branching track (in meters) and the tangent of the frog angle. The crossing may be straight, as in a crossover, or curved for other uses. The following designations are typical examples:
* 190-1:9, the most common switch, for 40 km/h on the branch track
* 300-1:9, preferred over 190-1:9 since the 1990s, for 50 km/h
* 500-1:12, for 60 km/h (signalled speed, capability: 65 km/h)
* 760-1:14, for 80 km/h
* 1200-1:18.5, for 100 km/h
* 2500-1:26.5, for 130 km/h (in Czech Rep, signalled speed is 120 km/h) (swingnose only)
In New South Wales standard turnouts of tangential types include:
* 1/7.5
* 1/8.25
** see als
NSW 1 in 8.25 crossing
* 1/10.5
* 1/12.0
* 1/15
Uganda
1 in 16, for 100 km/h;
General
Other considerations include the type of turnout (e.g. normal nose, swing nose, slips), wear and tear issues, and the weight and type of the vehicle passing over. Speeds for a trailing movement may be higher than for a facing movement. In many systems, speed limits vary depending on the type of train; for example, a turnout can have a "normal" speed limit for locomotive hauled trains, and a higher speed for multiple unit or high speed trains.
Turnouts with curved or tangential switch blades have higher speed than old style turnouts with straight switch blades.
Older turnouts use the same rail section, shaved down, for both stock rail and switch blade. Newer tangential turnouts use a stubbier rail section for the switch blade.
Assembly and transport
Turnouts are large pieces of rail infrastructure which may be too big, wide, or heavy to transport in one piece. Special wagons can carry the pieces at approximately 45° from vertical, so that they fit within the structure gauge
A structure gauge, also called the minimum clearance outline, is a diagram or physical structure that sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. It specifies the height and width of pl ...
. Once all the pieces have arrived, the turnout is assembled sleeper by sleeper on site. A set of turnouts may be trial assembled beforehand off site, to check that everything fits.
See also
* Abt automatic turnout
* Centralized traffic control
Centralized traffic control (CTC) is a form of railway signalling that originated in North America. CTC consolidates train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system cons ...
* Double junction
A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that c ...
* Gauntlet track
Gauntlet track or interlaced track (also gantlet track) is an arrangement in which railway tracks run parallel on a single track bed and are interlaced (i.e., overlapped) in such a way that only one pair of rails can be used at any time. Since th ...
* Junction (rail)
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. This implies a physical connection between the tracks of the two routes (assuming they are of the same gauge), provided by ''points'' ( ...
* Level junction
A level junction (or in the United Kingdom a flat crossing) is a railway junction that has a track configuration in which merging or crossing railroad lines provide track connections with each other that require trains to cross over in front o ...
* Minimum railway curve radius
*
* Rack railway switches
* Rail terminology (US/UK differences highlighted)
* Railway signal
A railway signal is a visual display device that conveys instructions or provides warning of instructions regarding the driver’s authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal mi ...
* Railway signalling
Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormo ...
* Railway turntable
In rail terminology, a railway turntable or wheelhouse is a device for turning railway rolling stock, usually locomotives, so that they can be moved back in the direction from which they came. Naturally, it is especially used in areas where ec ...
* Transfer table
A transfer table or traverser is a piece of railway equipment. It functions similarly to a turntable, although it cannot be used to turn vehicles around.
Overview
A transfer table, also known as a traverser, consists of a single length of track th ...
* Worldwide examples of gauntlet tracks
Gauntlet track or interlaced track (also gantlet track) is an arrangement in which railway tracks run parallel on a single track bed and are interlaced (i.e., overlapped) in such a way that only one pair of rails can be used at any time. Since th ...
References
Further reading
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External links
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{{Authority control
Articles containing video clips
Mechanisms (engineering)
Rail infrastructure
Rail junction types