Railroad switch
Overview
 
This article primarily uses North American terminology. British and Commonwealth terms are given in parentheses.


A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track
Rail tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...

 to another at a railway junction
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 , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...

.

The switch consists of the pair of linked tapering rails, known as points (switch rails or point blades), lying between the diverging outer rails (the stock rails).
Encyclopedia
This article primarily uses North American terminology. British and Commonwealth terms are given in parentheses.


A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track
Rail tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...

 to another at a railway junction
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 , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...

.

The switch consists of the 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
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

 coming from the narrow end toward the straight path or the diverging path. A train moving from the narrow end toward the point blades (i.e. it may go either left or right) is said to be executing a facing-point movement.

Unless the switch is locked, a train coming from either of the converging directs will pass through the points onto the narrow end, 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.

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 narrow end and a left-handed switch has the diverging track leaving to the opposite side.

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
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...

, in the same direction.

Operation

A railroad car
Railroad car
A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...

's wheel
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

s are guided along the tracks by coning of the wheels. Only in extreme cases does it rely on the flange
Flange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...

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 electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

 or by pneumatic
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 or hydraulic
Hydraulic machinery
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work. Heavy equipment is a common example.In this type of machine, hydraulic fluid is transmitted throughout the machine to various hydraulic motors and hydraulic cylinders and which becomes pressurised according to...

 actuation
Actuator
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...

.

In a trailing-point movement, the wheels will force the points to the proper position. This is sometimes known as running through the switch. Some switches are designed to be forced to the proper position without damage. Examples include variable switches, spring switches, and weighted switches.

If the points are rigidly connected to the switch control mechanism, the control mechanism's linkages may be bent, requiring repair before the switch is again usable. For this reason, switches are normally set to the proper position before performing a trailing-point movement.

An example of a mechanism that would require repair after a run-through in the trailing direction is a clamp-lock. This mechanism is popular in the UK, but the damage caused is common to most types of switches.

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 200 km/h (124.3 mph) or more is allowed.

The conventional way to increase turnout speeds is to lengthen the turnout and use a shallower frog angle. If the frog angle is so shallow that a fixed frog cannot support a train's wheels, a swingnose crossing
Swingnose crossing
A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...

 (US: moveable point frog) will be used. Higher speeds are possible without lengthening the turnout by using uniformly curved rail and a very low entry angle.

An AREMA (American Railway Engineering and Maintenance of Way Association) design number 20 turnout has a diverging speed limit of 45 miles per hour (72.4 km/h).

Operation in cold conditions

In cold conditions, snow and ice can prevent the correct operation of switches. In the past, people were employed by railway companies to keep the switches clear by sweeping the snow away, and this is still used in some countries, especially on minor lines. Some were provided with gas torches for melting ice. More recently, switches have had heaters installed in the vicinity of the points so that the temperature of the rails in these areas can be kept above freezing. The heaters may be powered by gas or electricity.
In cases where gas or electric heaters are unable to be used due to logistical or economical constraints anti-icing chemicals can be applied to create a barrier between the metal surfaces of the switch and ice.

Tram and monorail systems

The switch points of tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

 lines are often operated remotely by the driver
Driving
Driving is the controlled operation and movement of a land vehicle, such as a car, truck or bus.Although direct operation of a bicycle and a mounted animal are commonly referred to as riding, such operators are legally considered drivers and are required to obey the rules of the road...

, who intentionally draws power or not when passing under a special short segment of the overhead wire. Alternatively in modern times, radio telemetry or the like is used.

Monorail
Monorail
A monorail is a rail-based transportation system based on a single rail, which acts as its sole support and its guideway. The term is also used variously to describe the beam of the system, or the vehicles traveling on such a beam or track...

 systems have special switches.

Roller coaster switches

Many roller coasters have switches for the siding, or even for a double station system, for example in Disneyland Resort Paris
Disneyland Resort Paris
Disneyland Paris is a holiday and recreation resort in Marne-la-Vallée, a new town in the eastern suburbs of Paris, France. The complex is located from the centre of Paris and lies for the most part within the commune of Chessy, Seine-et-Marne....

' Space Mountain
Space Mountain (Disneyland, Paris)
Space Mountain: Mission 2 is a steel roller coaster-type attraction in Discoveryland at Disneyland Park in Disneyland Paris themed around a journey into space. The attraction opened on June 1, 1995, three years after the opening of the park, as a revival of interest to draw more guests to the...

 and Air
Air (roller coaster)
Air is a steel flying roller coaster located in the Forbidden Valley area of Alton Towers in Staffordshire, England. The ride was the first flying roller coaster designed by the Swiss manufacturers Bolliger & Mabillard...

 at Alton Towers
Alton Towers
Alton Towers is a theme park and resort located in Staffordshire, England. It attracts around 2.7 million visitors per year making it the most visited theme park in the United Kingdom. Alton Towers is also the 9th most visited theme park in Europe...

.

Regular rail can cross its own track because the gaps in the rails for wheel flanges are narrow, permitting the bladed design in this article. Round pipe roller coaster rails and box beam monorail rails usually have wheels riding at angles other than on top. These additional other angle wheels are a larger loading gauge
Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...

, requiring big gaps in the rail (structure gauge
Structure gauge
The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse...

) 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 the entire rail truss, fixed at one end, to point towards an alternate destination requires manipulating a long segment of rail. Substituting a segment requires placing two or more segments of rail on flat plate that is moved in its entirety to provide straight or curved track.
Alternatively these substitution track segments can be wrapped around a rotating cylinder, creating a triangular truss or a two sided plate. Rotating a table with a curved track segment in a Y junction is the less used third option. If the curved track turns the cars 60 degrees, and three rail lines meet as three equally spaced spokes, 120 degrees apart, then the curved track sitting on a turn table can be rotated to connect any two of the three rail lines at this junction, creating a triangle junction.


Classification

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.

Safety

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

Perhaps the greatest security challenge in railway operation is preventing the tampering of manually-operable switches. Similar (non-fatal) wrecks near Newport News, Virginia
Newport News, Virginia
Newport News is an independent city located in the Hampton Roads metropolitan area of Virginia. It is at the southeastern end of the Virginia Peninsula, on the north shore of the James River extending southeast from Skiffe's Creek along many miles of waterfront to the river's mouth at Newport News...

 on and in Stewiacke, Nova Scotia
Stewiacke, Nova Scotia
-External links:* *...

 on resulted from switches being thrown open in front of the trains by teenage saboteur
Saboteur
A saboteur is someone who commits sabotage.It may also refer to:*Morituri , a 1965 film also known as The Saboteur*Saboteur , a card game by Frederic Moyersoen, published in 2004...

s. To prevent these incidents, most unused switches are locked up.

The 1998 Eschede train disaster
Eschede train disaster
The Eschede train disaster was the world's deadliest high-speed train accident. It occurred on 3 June 1998, near the village of Eschede in the Celle district of Lower Saxony, Germany. The toll of 101 people dead and 88 injured surpassed the 1971 Dahlerau train disaster as the deadliest accident in...

 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.

In 1980, 18 people died in the Buttevant Rail Disaster
Buttevant Rail Disaster
Buttevant Rail Disaster was a train crash that occurred 137 miles from Heuston Station on the Dublin to Cork mainline at Buttevant Railway Station, County Cork in the Republic of Ireland on 1 August 1980. At 12:45 the 10:30am Dublin to Cork express train entered Buttevant station carrying some...

 at Buttevant
Buttevant
Buttevant 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 earlier settlement of the Donegans, Carrig Donegan, the origins of the present town are clearly and...

, Co. Cork in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, when the Dublin-Cork
Cork (city)
Cork is the second largest city in the Republic of Ireland and the island of Ireland's third most populous city. It is the principal city and administrative centre of County Cork and the largest city in the province of Munster. Cork has a population of 119,418, while the addition of the suburban...

 express was derailed at high speed after being inadvertently switched into a siding via ground frame operated points.

The Potters Bar rail crash
Potters Bar rail crash
There have been at least three railway accidents in Potters Bar, a town in Hertfordshire, United Kingdom, just north of Greater London. One occurred in 1898, one in 1946 and the last in 2002.-1898:...

 at Potters Bar
Potters Bar
Potters Bar is a town in the Hertsmere borough of Hertfordshire, England, located north of Central London. In 2001 it had a population of 21,618....

, Hertfordshire
Hertfordshire
Hertfordshire is a ceremonial and non-metropolitan county in the East region of England. The county town is Hertford.The county is one of the Home Counties and lies inland, bordered by Greater London , Buckinghamshire , Bedfordshire , Cambridgeshire and...

 in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 occurred in May 2002, 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
Railway platform
A railway platform is a section of pathway, alongside rail tracks at a train station, metro station or tram stop, at which passengers may board or alight from trains or trams. Almost all stations for rail transport have some form of platforms, with larger stations having multiple platforms...

 ahead. Fortunately, the movement of the switch occurred beneath the final coach, so that although 7 people were killed, the front coaches remained on the tracks. Poor maintenance of the points was found to be the primary cause of the crash.

The initial conclusion of the inquiry into the Grayrigg derailment
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 North West England. The initial conclusion of the accident investigation is that the derailment was caused by a faulty set of points ,...

 of blames an incorrectly maintained set of points.

History

On early lines, vehicles were moved between tracks by means of sliding rails. The switch as we know it was patented by Charles Fox in 1832.

Prior to the widespread availability of electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

, switches at heavily-traveled junctions
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 , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...

 were operated from a signal box
Signal box
On a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable...

 constructed near the tracks through an elaborate system of rods and lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

s. The levers were also used to control railway signal
Railway signal
A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...

s to control the movement of trains over the points. Eventually, mechanical systems known as interlocking
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 referred to as an interlocking plant...

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. On some low-traffic branch lines, in self-contained marshalling yards, or on heritage railway
Heritage railway
thumb|right|the Historical [[Khyber train safari|Khyber Railway]] goes through the [[Khyber Pass]], [[Pakistan]]A heritage railway , preserved railway , tourist railway , or tourist railroad is a railway that is run as a tourist attraction, in some cases by volunteers, and...

s, switches may still be operated in this way.

Points (point blades)

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.

Frog (common crossing)

The frog, also known as the common crossing (or K-Rail in Australian terminology), refers to 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 of manganese steel. On lines with heavy use the casting may be treated with explosive shock hardening
Shock hardening
Shock hardening is a process used to strengthen metals and alloys, wherein a shock wave produces atomic-scale defects in the material's crystalline structure. As in cold work, these defects interfere with the normal processes by which metallic materials yield , making materials stiffer, but more...

 to increase service life. A frog forms part of a railroad switch, and is also used in a level junction
Level junction
In U.S. railroad practice, a level junction 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 of opposing traffic at grade In U.S. railroad practice, a level junction...

 (flat crossing). The frog is designed to ensure the wheel crosses the gap in the rail without "dropping" into the gap; the wheel and rail profile ensures that the wheel is always supported by at least one rail. To ensure that the wheels follow the appropriate flangeway, a check-rail ("guard rail" North American terminology) is installed inside the rail opposite the frog.

On lines with heavy and/or high-speed traffic, a swingnose crossing
Swingnose crossing
A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...

 (moveable 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 shape of the device resembling a leaping frog with legs extended forward and to the rear of the body.

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

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 exist to 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. These frogs are for low-speed use and are common in rail yards
Classification yard
A classification yard or marshalling yard is a railroad yard found at some freight train stations, used to separate railroad cars on to one of several tracks. First the cars are taken to a track, sometimes called a lead or a drill...

.
Check rails are often used on really sharp curves, even where there are no switches.

Switch motor

A switch motor (also known as a switch machine, point motor or point machine
Point machine
A point machine is a device for operating railway turnouts especially at a distance.-Overview:In the earliest times, railway turnouts were operated manually by simple levers...

) is an electric
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

, hydraulic or pneumatic mechanism that aligns the points with one of the possible routes. 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.
A patent by W. B. Purvis
1897 in rail transport
- March events :* March 24 - Construction begins on the Sierra Railway of California, now known as the Sierra Railroad, between Oakdale and Jamestown, California.- May events :...

 dates from 1897.

Points lever

A points lever, ground throw, or switchstand is a lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

 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
Railroad tie
A railroad tie/railway tie , or railway sleeper is a rectangular item used to support the rails in railroad tracks...

 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
Lever frame
Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals and points to allow the safe operation of trains in the area the signals control...

 or ground frame. To prevent the tampering of switches by outside means, these switches are locked up when not in use.

Point Machine Conversion - Manual to Motorized

A point machine conversion system consist in a remotely controlled device attached to an existing manually-operated point that allows the shunter/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

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 proving that they are in the correct position. The "facing point" part of the name refers to the fact that they are to 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.

In the United Kingdom, FPLs were incredibly common from an early date, due to laws being passed which forced the provision of FPLs for any routes travelled 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 rails are somewhat flexible it is possible to make this join by thinning a short section of the rail 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 25 mm (0.984251968503937 in) 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.

Types of switches

Apart from the standard right-hand and left-hand switches, switches commonly come in various combinations of configurations.

Double slip

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, as well as 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 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 America, the arrangement may also be called a double switch, or more colloquially, a puzzle switch. The Great Western Railway
Great Western Railway
The Great Western Railway was a British railway company that linked London with the south-west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835 and ran its first trains in 1838...

 in the United Kingdom used the term double compound points, and the switch is also known as a double compound in Victoria (Australia)
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....

.

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

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;
  • 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 and the scissors crossover, double outside slip switches are only used in rare, specific cases.

Crossover

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 overlap 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
Level junction
In U.S. railroad practice, a level junction 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 of opposing traffic at grade In U.S. railroad practice, a level junction...

.

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 the switches must be changed for each train. For this reason, on some high-capacity rapid transit
Rapid transit
A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 systems, crossovers between local and express tracks are not used during normal rush hour
Rush hour
A rush hour or peak hour is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest. Normally, this happens twice a day—once in the morning and once in the evening, the times during when the most people commute...

 service, and service patterns are planned around use of the usually flying junctions at each end of the local-express line.
In Germany a crossover is known as an Überleitstelle (abbreviated to: Üst) and is defined as an operating control point on the open line. It is also a block section. At an Überleitstelle trains can transfer from one track of a single or double track section of route to another track on a double track section on the same route. Depending on the safety equipment provided, trains may run this other track either by exception or routinely against the normal direction of traffic.

An Überleitstelle must have at least one turnout
Turnout
Turnout may refer to:* Turnout , a rotation of the leg which comes from the hips, causing the knee and foot to turn outward, away from the center of the body* Turnout , a British film...

. On double tracked routes, single and double crossovers are common, each one consisting of two turnouts and an intermediate section. Very often - but not mandatory - the turnouts and block signals at an Überleitstelle are remotely controlled or set from a central signal box.
The official categorisation of an Überleitstelle as a type of junction
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 , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...

 first arose in Germany with the construction of high-speed railways. Previous to that there were already operating control points at which trains could just transfer from one track to another on the same route, but they were considered as junctions (Abzweigstelle). The latter are still used to refer to those places in stations
Train station
A train station, also called a railroad station or railway station and often shortened to just station,"Station" is commonly understood to mean "train station" unless otherwise qualified. This is evident from dictionary entries e.g...

 which enable 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 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
Harp switch stand
A harp switch stand is a type of railroad switch stand that was most common during the 19th century in the United States. The name derives from the characteristic shape of the stand. The harp stand was typically used in conjunction with the stub switch...

.

The rails leading up to a stub switch are not secured to the sleepers
Railroad tie
A railroad tie/railway tie , or railway sleeper is a rectangular item used to support the rails in railroad tracks...

 for several feet, and rail alignment across the gap is not positively enforced. Stub switches also require some flexibility
Flexibility
Flexibility may refer to:* Flexibility , the distance of motion of a joint, which may be increased by stretching* Flexibility , in the field of engineering systems design, designs that can adapt when external changes occur...

 in the 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.

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 lines and branch line
Branch line
A branch line is 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...

s. Some modern monorail switches use the same principle.

Plate switch

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.

Three-way switch

A three-way switch is used to split a railroad track into three divergent paths rather than the more usual two. The complexity of such arrangements usually results in severe speed restrictions, and therefore three-way switches are usually only used in a station or depot where space is restricted and low speeds are normal.
Stub switches can more readily select between three routes, so most three-way switches are stub switches, although some were built using points. It was extremely difficult to hold the two rails the correct distance apart for the length of the switch with these types of switch.
A three-way switch from a Brisbane tram depot is shown on the right. This example has two points (point blades) on each track, allowing for three diverging routes. The points can both be set to one side, resulting in a vehicle turning off the straight track. Alternatively, the two blades can be separated if the vehicle must continue along the straight track.

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

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.

Run-off points

Run-off points are used to protect main lines from stray or runaway railroad car
Railroad car
A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...

s or from trains passing signals set at danger. In these cases, vehicles would otherwise roll onto and obstruct a main line (sometimes known as fouling) and cause an accident. 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 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 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 train. These trains did not have a mechanism in place to automatically brake runaway cars. Catch points were therefore required to stop the rear portion of a train that had become divided, although they would 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 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 derailer, 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.

Dual gauge switches

Dual gauge switches are used in dual gauge
Dual gauge
A dual-gauge or mixed-gauge railway has railway track that allows trains of different gauges to use the same track. Generally, a dual-gauge railway consists of three rails, rather than the standard two rails. The two outer rails give the wider gauge, while one of the outer rails and the inner rail...

 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 rails (railroad)
In railroad use, guard rails are placed parallel to regular running rail along areas of restrictive clearance, such as a bridge, trestle, or tunnel. These have the effect of keeping the wheels of rolling stock in alignment in case of derailment...

 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 switches are as varied as rack railway
Rack railway
A rack-and-pinion railway is a 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 this rack rail...

 technologies. Where use of the rack is optional, as on the Zentralbahn
Zentralbahn
The Zentralbahn is a Swiss railway company that was created on January 1, 2005, with the merger of the Luzern–Stans–Engelberg-Bahn and the Brünigbahn...

 in Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

 or the West Coast Wilderness Railway
West Coast Wilderness Railway
The West Coast Wilderness Railway, Tasmania is a reconstruction of the Mount Lyell Mining and Railway Company railway between Queenstown and Regatta Point...

 in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

, 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
Dolderbahn
The Dolderbahn is a long rack railway in the Swiss city of Zurich, and is owned by the Dolderbahn-Betriebs AG. The line was opened in 1895 as a funicular railway, and converted to rack operation in 1973...

 in Zurich
Zürich
Zurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...

, Štrbské Pleso
Štrbské Pleso railway station
Štrbské Pleso railway station is a junction station in the High Tatras. It serves the settlement of Štrbské Pleso, which is part of the village of Štrba, in the Prešov Region, northeastern Slovakia....

 in Slovakia
Slovakia
The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...

 and the Schynige Platte
Schynige Platte
The Schynige Platte is a Swiss mountain region near Wilderswil where the Schynige Platte Railway ends .In good weather conditions the summit offers spectacular views to many surrounding mountains, including Jungfrau, Eiger, Silberhorn and others, as well as Thunersee and Brienzersee...

 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.

Switch diamond

Although not strictly speaking a turnout, a switch diamond
Level junction
In U.S. railroad practice, a level junction 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 of opposing traffic at grade In U.S. railroad practice, a level junction...

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 crossing
Swingnose crossing
A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...

s 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 (centre-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. Remember that both wheels on an axle hit the crossing gaps almost simultaneously. Switching the blades like the photo shows allows a much higher speed across the gap.

The frog end is not as bad, because the outer rail is still continuous, the wing rail (the bit that bends away after the frog gap) provides a gradual transition, and the check rail avoids the possibility of points splitting. Note how the wing rail has a wider shiny section, showing how the wheel load is transferred across the gap.

Single-point switch

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
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

) systems using grooved rails, if the wheels on both sides of the car are connected by a solid axle, only one switchpoint is needed to steer it onto one or the other track. The opposite wheel is supported for a short distance by its flange running in the groove.

Expansion joint

Expansion joint
Expansion joint
An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, to hold certain parts together, or to allow movement due to ground settlement or earthquakes...

s are a construction that allows the rails to move relative to each other due to changes in temperature while retaining continuity for through traffic. They are often used on large bridges such as the Sydney Harbour Bridge
Sydney Harbour Bridge
The Sydney Harbour Bridge is a steel through arch bridge across Sydney Harbour that carries rail, vehicular, bicycle and pedestrian traffic between the Sydney central business district and the North Shore. The dramatic view of the bridge, the harbour, and the nearby Sydney Opera House is an iconic...

.

Turnout speeds

Turnout speeds are governed by a number of factors.

As a general rule, the finer the crossing angle of a turnout, the higher the turnout speed.
In USA, turnouts are rated by number, 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 is twice the number.
  • #10 - 15 mph (24.1 km/h)
  • #15 - 30 mph (48.3 km/h)
  • #20 - 40 mph (64.4 km/h)


In Russia and CIS switches a marked with tangent
Tangent
In geometry, the tangent line to a plane curve at a given point is the straight line that "just touches" the curve at that point. More precisely, a straight line is said to be a tangent of a curve at a point on the curve if the line passes through the point on the curve and has slope where f...

 of crossing angle:
  • 1/6 - sorting yards only, whenever it is impossible to install a better switch
  • 1/9 - 40 km/h (24.9 mph), the most common switch, installed by default.
  • 1/11 - 50 km/h (31.1 mph), used where passenger trains follow a diverging path. Swingnose crossing may be installed if required.
  • 1/18 - 80 km/h (49.7 mph), used where either non-interruptible movement is required or the mainline derives from the branch line.
  • 1/22 - 120 km/h (74.6 mph), rarely used, hi-speed lines only.


Other considerations include the type of turnout (e.g. normal or swing nose, or slips etc.), 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.

See also

  • Centralized traffic control
    Centralized traffic control
    Centralized traffic control is a form of railway signalling that originated in North America and centralizes train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that...

  • Double junction
    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 carries traffic through the junction at reduced speed.A...

  • Expedition Everest
    Expedition Everest
    Expedition Everest - Legend of the Forbidden Mountain is a roller coaster attraction at Disney's Animal Kingdom theme park at the Walt Disney World Resort in Lake Buena Vista, Florida, near Orlando...

    , roller coaster
    Roller coaster
    The roller coaster is a popular amusement ride developed for amusement parks and modern theme parks. LaMarcus Adna Thompson patented the first coasters on January 20, 1885...

     with switches
  • Minimum railway curve radius
    Minimum railway curve radius
    The minimum railway curve radius, the shortest design radius, has an important bearing on constructions costs and operating costs and, in combination with superelevation in the case of train tracks, determines the maximum safe speed of a curve. Superelevation is not a factor on tramway tracks...

  • Rail terminology
    Rail terminology
    Rail terminology is a form of technical terminology. The difference between the American term railroad and the international term railway is the most obvious difference in rail terminology...

     (US/UK differences highlighted)

  • Railway signal
    Railway signal
    A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...

  • Railway signalling
    Railway signalling
    Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...

  • Railway switching networks
  • Turntable (rail)


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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