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Catch points and trap points are types of turnout which act as
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 ...
safety Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to risk management, the control of recognized hazards in order to achieve an acceptable level of risk. Meanings There are ...
devices. Both work by guiding railway carriages and trucks from a dangerous route onto a separate, safer track. Catch points are used to
derail A derail or derailer is a device used to prevent fouling (blocking or compromising) of a rail track (or collision with anything present on the track, such as a person, or a train) by unauthorized movements of trains or unattended rolling stock. ...
vehicles which are out of control (known as ''runaways'') on steep slopes. Trap points are used to protect main railway lines from unauthorised vehicles moving onto them from sidings or
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 industri ...
s. Either of these track arrangements may lead the vehicles into a sand drag or safety siding, track arrangements which are used to safely stop them after they have left the main tracks. A
derail A derail or derailer is a device used to prevent fouling (blocking or compromising) of a rail track (or collision with anything present on the track, such as a person, or a train) by unauthorized movements of trains or unattended rolling stock. ...
is another device used for the same purposes as catch and trap points.


Trap points

''Trap points'' are found at the exit from a siding or where a secondary track joins a main line. A facing turnout is used to prevent any unauthorised movement that may otherwise obstruct the main line. The trap points also prevent any damage that may be done by a vehicle passing over points not set for traffic joining the main line. In the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, the use of trap points at siding exits is required by government legislation. An unauthorised movement may be due to a runaway
wagon A wagon or waggon is a heavy four-wheeled vehicle pulled by draught animals or on occasion by humans, used for transporting goods, commodities, agricultural materials, supplies and sometimes people. Wagons are immediately distinguished from ...
, or may be a train passing a signal at danger. When a
signal 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'' ...
controlling passage onto a main line is set to "danger", the trap points are set to derail any vehicle passing that signal.
Interlocking In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junction (rail), junctions or crossings. The signalling appliances and Track (rail transpor ...
is used to make sure that the signal cannot be set to allow passage onto the main line until the trap points have been aligned to ensure this movement can take place. Trap points should preferably be positioned to ensure that any unauthorised vehicle is stopped a safe distance from the main line. However, due to space limitations, it is not always possible to guarantee this. If the lines are
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 ...
ed and a wagon or train using the catchpoint could foul an adjacent line, then a
track circuit interrupter A track circuit interrupter may be fitted at catch points, trap points or buffer stops to maintain a track circuit in the 'occupied' state in the event of a derailment. The track circuit remains de-energised until the interrupter is replaced. ...
will be fitted to one of the run-off rails. When a train runs off it will break the track circuit and set main line signals to 'danger'.


Types

There are several different ways of constructing trap points: * A ''single tongue trap'' consists of only one switch rail, leading away from the main line to a short tongue of rail. This is usually placed in the rail farthest from the main line. * ''Double trap points'' are a full turnout, leading to two tongues. Usually the tongue nearer the main line is longer than the other. * ''Trap points with a crossing'' are double trap points where the tongues of rail are longer, so that the trap point rail nearest the main line continues over the siding rail with a common crossing or frog. * A ''trap road with stops'' is a short dead-end siding leading to some method of stopping a vehicle, such as a sand drag or
buffer stop A buffer stop, bumper, bumping post, bumper block or stopblock (US), is a device to prevent railway vehicles from going past the end of a physical section of track. The design of the buffer stop is dependent, in part, on the kind of couplings ...
. * ''Wide to gauge trap points'' have switches that work in opposite directions and are therefore either both open or both closed. Vehicles derailed at these points will tend to continue in a forward direction rather than being thrown to one side. Wide to gauge points are typically found on sidings situated between running lines. The type of trap points to be used depends on factors such as the
gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
of the siding, and whether
locomotive A locomotive or engine is a rail transport vehicle that provides the Power (physics), motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, Motor coach (rail), motor ...
s enter the siding. * ''Independent switches'' are a kind of wide to gauge switch which are part of two separate crossovers. There are three positions: part of crossover A to left; wide to gauge switches; part of crossover B to right. A good place to view these independent switches are at both ends of Platforms 1 and 2 at
Hornsby railway station Hornsby railway station is located at the junction of the Main Northern and North Shore lines, serving the Sydney suburb of Hornsby. It is served by Sydney Trains T1 North Shore Line and T9 Northern Line services and NSW TrainLink Interc ...
, Sydney. File:StokeGiffordYard-catchpoints.jpg, Double trap points protecting the
South Wales Main Line The South Wales Main Line ( cy, Prif Linell De Cymru), originally known as the London, Bristol and South Wales Direct Railway or simply as the Bristol and South Wales Direct Railway, is a branch of the Great Western Main Line in Great Britain. ...
at the exit of Stoke Gifford Rail Yard near
Bristol Parkway railway station Bristol Parkway, on the South Wales Main Line, is in the Stoke Gifford area in the northern suburbs of the Bristol conurbation. It is from London Paddington. The station was opened in 1972 by British Rail, and was the first in a new generat ...
File:Castle Cary catch points - 02.jpg, Double trap points with much longer rails, at
Castle Cary railway station Castle Cary railway station is on the Reading to Taunton line south west of London Paddington and the Bristol to Weymouth line south of Bristol Temple Meads. The two routes share tracks between Westbury and Castle Cary stations and are bot ...
File:Schutzweiche.jpg, A trap road with buffer stops at the railway station of ''Allersberg'', on the Nuremberg-Munich high-speed rail line Strasbourg_aiguillage-déraillant.jpg, trap point in France
''Catch points'' are used where track follows a rising
gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
. They are used to
derail A derail or derailer is a device used to prevent fouling (blocking or compromising) of a rail track (or collision with anything present on the track, such as a person, or a train) by unauthorized movements of trains or unattended rolling stock. ...
(or "catch") any unauthorised vehicles travelling down the gradient. This may simply be a vehicle that has accidentally been allowed to run away down the slope, or could be a wagon that has decoupled from its train. In either case, the runaway vehicle could collide with a train farther down the slope, causing a serious accident. Catch points may consist of a full turnout or a single switch blade. In some cases, on a
track Track or Tracks may refer to: Routes or imprints * Ancient trackway, any track or trail whose origin is lost in antiquity * Animal track, imprints left on surfaces that an animal walks across * Desire path, a line worn by people taking the shorte ...
that is only traversed by uphill traffic, trailing point blades are held in a position to derail any vehicle travelling downhill. However, any traffic travelling in the correct (uphill) direction can pass over the turnout safely, pushing the switch blades into the appropriate position. Once the wheels have passed, the catch points are forced back into the derailing position by
spring Spring(s) may refer to: Common uses * Spring (season) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...
s. In these cases, a lever may be provided to temporarily override the catch points and allow safe passage down the gradient in certain controlled circumstances. The use of catch points became widespread in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
after the
Abergele rail disaster The Abergele rail disaster, which took place near Abergele, North Wales, in August 1868, was the worst railway disaster in Great Britain up till then. The Irish Mail train was on its way from London to Holyhead, when a complicated shunting ope ...
(1868), where runaway wagons containing paraffin oil (kerosene) collided with an
express train An express train is a type of passenger train that makes a small number of stops between its origin and destination stations, usually major destinations, allowing faster service than local trains that stop at most or all of the stations alo ...
. Catch points continued to be used in the UK until the mid-20th century. At this time, continuous automatic brakes, which automatically stop any vehicles separated from their train, were widely adopted, making catch points largely obsolete.


Wide to gauge catch points

Sometimes a track is located between two other tracks that are converging, and there is nowhere for a catchpoint to divert a train to. In such cases, a pair of single catchpoints of left and right hand may be provided to derail the overrunning train without directing it to either side. The two blades of an ordinary turnout may also be operated separately for the same purpose. Examples would be the north and south ends of platforms 1 and 2 at Hornsby in
New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...
.


Sand drag

In some cases, catch points and trap points direct vehicles into a ''sand drag'' or ''safety siding'', also sometimes called an ''arrestor bed''. This may be a siding simply leading to a mound of
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
,
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...
or other granular material, or a siding where the rails are within sand-filled troughs. This method of stopping a vehicle travelling at speed is preferred over a
buffer stop A buffer stop, bumper, bumping post, bumper block or stopblock (US), is a device to prevent railway vehicles from going past the end of a physical section of track. The design of the buffer stop is dependent, in part, on the kind of couplings ...
as there is less
shock Shock may refer to: Common uses Collective noun *Shock, a historic commercial term for a group of 60, see English numerals#Special names * Stook, or shock of grain, stacked sheaves Healthcare * Shock (circulatory), circulatory medical emergen ...
to the vehicle involved.


Chock block

A cheap and simple alternative to catch points or a derail is a chock block, which is a piece of timber that can be positioned and locked over one of the rails at the end of a siding to protect the main line from runaways. In order for the siding to be used the chock block must be removed.


Effectiveness

Because catch points are rarely needed, it is not always clear whether they will in fact derail a runaway train effectively and as safely as possible. For example, use of catch points to derail a train that had
passed a signal at danger A signal passed at danger (SPAD), known in the United States as a stop signal overrun and in Canada as passing a stop signal, is an event on a railway where a train passes a stop signal without authority. In the United States and Canada, this ...
at
London Paddington Paddington, also known as London Paddington, is a London station group, Central London railway terminus and London Underground station complex, located on Praed Street in the Paddington area. The site has been the London terminus of services pro ...
station in June 2016 resulted in the empty train, a Class 165, hitting and severely damaging an overhead line electrification stanchion, causing all services to and from the station to be halted for hours.


Accidents

In 2010, in snowy conditions, at
Carrbridge Carrbridge ( sco, Carrbrig, gd, Drochaid Chàrr) is a village in Badenoch and Strathspey in the Scottish Highlands. It lies off the A9 on the A938, west of Skye of Curr and southeast of Tomatin, near Bogroy. It has the oldest stone bridge i ...
, a Class 66 passed a red signal as well as catch points, leading to the train going down the embankment, injuring the two crew on board.


See also

*
Buffer stop A buffer stop, bumper, bumping post, bumper block or stopblock (US), is a device to prevent railway vehicles from going past the end of a physical section of track. The design of the buffer stop is dependent, in part, on the kind of couplings ...
*
Derail A derail or derailer is a device used to prevent fouling (blocking or compromising) of a rail track (or collision with anything present on the track, such as a person, or a train) by unauthorized movements of trains or unattended rolling stock. ...
*
Runaway train A runaway train is a type of railroad incident in which unattended rolling stock is accidentally allowed to roll onto the main line, a moving train loses enough braking power to be unable to stop in safety, or a train operates at unsafe speeds d ...
*
Runaway truck ramp A runaway truck ramp, runaway truck lane, escape lane, emergency escape ramp, or truck arrester bed is a traffic device that enables vehicles which are having braking problems to safely stop. It is typically a long, sand- or gravel-filled lane co ...
*
Runway safety area A runway safety area (RSA) or runway end safety area (RESA) is defined as "the surface surrounding the runway prepared or suitable for reducing the risk of damage to airplanes in the event of an undershoot, overshoot, or excursion from the runway. ...
(RSA/RESA) for airplanes


References


External links

*
Illustrated explanation of catch points at Springwell

Steam locomotive derailed by catch points
at
Great Central Railway The Great Central Railway in England was formed when the Manchester, Sheffield and Lincolnshire Railway changed its name in 1897, anticipating the opening in 1899 of its London Extension. On 1 January 1923, the company was grouped into the ...
— video footage on YouTube {{Railwaysignalling Railway safety Railway track layouts