Part of a
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 enormou ...
system, a train stop, trip stop or tripcock (sometimes called a tripper) is a
train protection device that automatically stops 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 Passenger train, transport people or Rail freight transport, freight. Trains are typically pul ...
if it attempts to pass 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'' ...
when the signal aspect and operating rules prohibit such movement, or (in some applications) if it attempts to pass at an excessive speed.
Basic operation
![Train-trip-lever](https://upload.wikimedia.org/wikipedia/commons/e/e4/Train-trip-lever.jpg)
The train stop system comprises two basic components. One is the trip arm mechanism, mounted on the ground adjacent to the
rail
Rail or rails may refer to:
Rail transport
*Rail transport and related matters
*Rail (rail transport) or railway lines, the running surface of a railway
Arts and media Film
* ''Rails'' (film), a 1929 Italian film by Mario Camerini
* ''Rail'' ( ...
, which essentially consists of a spring-loaded arm connected to an
electric motor
An electric motor is an Electric machine, 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 Electromagneti ...
(or pneumatic cylinder in electro-pneumatic systems). The other is the train-mounted trip
cock, which is connected either directly or electrically to the train's
braking system
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Background ...
.
The trip arm is raised automatically whenever a train should be brought to a halt. When the signalling system determines it is safe for the train to proceed, the motor drives the trip arm down to the lowered position. The
spring
Spring(s) may refer to:
Common uses
* Spring (season), a season of the year
* Spring (device), a mechanical device that stores energy
* Spring (hydrology), a natural source of water
* Spring (mathematics), a geometric surface in the shape of a ...
ensures that the trip arm is raised in all other situations, which is an essential
fail-safe
In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safe ...
provision in case of failure of the electric or pneumatic power supply or of the motor driving the trip arm. If a train attempts to pass the signal with the trip arm in the raised position, the trip arm makes mechanical contact with the trip cock on the train, causing the train's brakes to be automatically applied, thereby bringing the train to a halt.
Wayside trip arms are adjusted so that they rise to a point approximately above the top of the running rail when in the stop position, and lower to approximately below the top of the running rail when clear. The time taken for the arm to rise or be lowered is approximately two seconds.
Restrictions
The mechanical train stops have been found to be relatively safe with their historic models from the 19th century to be still in use in the 21st century. Because of the quadratic force increments in relation to speed these mechanical systems are restricted to low speed applications. Their continued usage can be found in urban rapid transit systems with trains making no more than 100 km/h. Whereas later contactless train stops require a working receiver on the train to initiate the emergency stop (as for
PCCS or
Indusi) the mechanical stops have initially been kicking the brakes directly.
Because the trip arm may hit the brake lever directly, there have been installations where every wagon of a train has a separate trip cock on each bogie that has brakes. Hence in some installations the trip arm will be folded back to the safe position only a few seconds after a signal has turned red in order to reduce
wear
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology.
Wear in m ...
(which is an actual security risk as shown in the
1995 Russell Hill subway accident
The 1995 Russell Hill subway accident was a deadly train crash that occurred in Toronto, Ontario, Canada, on Line 1 Yonge–University of the Toronto subway on August 11, 1995. Three people were killed and 30 were taken to hospital with injuries ...
). Because of wear the trip arms for the opposite direction on the same rail will be actuated along with the trip arm for the nominal direction.
Like many early systems a mechanical train stop does not inherently control speed. There were accidents where trains had overrun the overlap due to excessive speed. In order to externally control the speed of a train the operation of
timed train stops has been deployed as it is widely used on the New York City Subway, where a second trip arm at a distance is folded down only a few seconds after a train has passed a check point. These expensive speed control systems are generally phased out in favour of a cab control computer that can continuously check a braking curve while approaching a signal.
Types of train stops
There are three types of train stops:
*Trip stop - stops train trying to pass red signal
*Timed train stop - stops train moving too fast
*Fixed train stop - prevents any trains from passing a point
Trip stops
The trip arm is raised whenever the signal is not displaying a proceed aspect. If a train tries to pass the signal, the trip cock on the train strikes the raised trip arm and the train is brought to a halt. When the signal indicates it is safe to proceed ''(clear or caution)'', the trip arm is lowered, and a train is able to proceed without further hindrance. In some cases, the trip arm will not be lowered when the signal to which it applies is exhibiting a proceed indication, e.g. when subsidiary signals are cleared, forcing a train to trip before proceeding, thus ensuring that movements are conducted at safe speeds.
Timed train stops
With a timed train stop, the trip arm stays raised until the approaching train has shunted a
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 ...
on the approach for a period of time corresponding to a set speed. If the train approaches at a speed higher than the one that is set, the trip arm remains raised and trips the train to a stop. If the train approaches at a speed equal to or lower than the set speed, the trip arm lowers before the train arrives, and the train is able to proceed without further hindrance.
Some timed train stops require the
driver to acknowledge a stimulus before the trip arm is lowered on a yellow signal.
For sections of track with lower speed limits (15–20 km/h) a simpler construction is also used. The trip arm rotates freely on a horizontal axis with a counterbalance attached to its lower end. If a train's speed is low, the arm will be rotated by the trip cock with a force insufficient to initiate braking. But if its speed is too high, force will be large due to the counterbalance
inertia
Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
, causing the brakes to be applied.
Fixed train stops
With fixed train stops, the trip arm cannot be lowered. Fixed stops are positioned close to the end of a dead-end track, to stop a train before it runs out of track. They may also be used at the end of track sections beyond which certain trains should not pass, such as the end of electrified territory (e.g.
Hamilton, NSW), or to test the automatic brake and tripgear of trains departing certain locations, e.g. storage sidings, near buffer stops.
A fixed train stop that is the last one on a running line in the reverse direction may, despite its name, be suppressed, as is the case with the associated "Fixed Signals" on the Sydney network. Suppression is needed because in Sydney, the rear trip cock on a train is always lowered, while in
Melbourne
Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
, by contrast, suppression is not required because the trip cock at the rear of a train is always raised clear of any wayside trip arm.
Some railways and rail transit agencies use fixed train stops to protect workers in work zones by temporarily applying them at either end of the zone, preventing trains from incorrectly entering the work zone.
Installations
In 1901,
Union Switch and Signal Company
Union Switch & Signal (commonly referred to as US&S) was an American company based in Pittsburgh, Pennsylvania, which focused on railway signaling equipment, systems and services. The company was acquired by Ansaldo STS (from 2015, Hitachi Rail ...
developed the first
automatic train stop
Automatic train stop or ATS is a system on a train that automatically stops a train if certain situations occur (unresponsive train operator, earthquake, disconnected rail, train running over a stop signal, etc.) to prevent accidents. In some scena ...
system for the
Boston Elevated Railway
The Boston Elevated Railway (BERy) was a streetcar and rapid transit railroad operated on, above, and below, the streets of Boston, Massachusetts and surrounding communities. Founded in 1894, it eventually acquired the West End Street Railwa ...
. This system was soon adopted by the
New York City Subway
The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October 2 ...
and other transit systems in the United States. Similar systems were installed around this time on the
London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
system.
Because of its mechanical nature, the train stop has certain limitations in application. Severe snow and ice conditions, for example, could interfere with operation of the wayside trip arm. Its widest application, therefore, is on underground
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 c ...
lines, where conditions that might interfere with proper operation are readily controlled.
Train stops on London Underground lines are gradually being phased out in favour of
ATP and distance-to-go signalling. Train stops remain standard equipment on all
RailCorp
Rail Corporation New South Wales (RailCorp) was an agency of the State of New South Wales, Australia established under the ''Transport Administration Act 1988'' in 2004. It was a division under the control of Transport for NSW since the latter' ...
metropolitan passenger lines in New South Wales, and on the electrified suburban railway system in
Melbourne
Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
, Australia.
The Train stops at the Berlin S-Bahn were first installed in the late 1920s. They are named ' (or ) because of their testing and first installation on the
Stettin Railway to the suburban town of
Bernau. This was the first
heavy rail
Various terms are used for passenger railway lines and equipment; the usage of these terms differs substantially between areas:
Rapid transit
A rapid transit system is an electric railway characterized by high speed (~) and rapid accelerati ...
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 c ...
system with third-rail electrification in Germany. They are being phased out in favour of the
ZBS system based on
Eurobalise
A Eurobalise is a specific variant of a balise being a transponder placed between the rails of a railway. These balises constitute an integral part of the European Train Control System, where they serve as "beacons" giving the exact location of a t ...
s until 2025.
Trackside installation
![Zugsicherung sbahn berlin](https://upload.wikimedia.org/wikipedia/commons/b/b2/Zugsicherung_sbahn_berlin.jpg)
*
Berlin S-Bahn
The Berlin S-Bahn () is a rapid transit railway system in and around Berlin, the capital city of Germany. It has been in operation under this name since December 1930, having been previously called the special tariff area ''Berliner Stadt-, Ring ...
rapid transit uses a metal bar as the trip arm, positioned at the height of the first
bogie
A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
, on which the trip cock is placed. The metal bar (also named "Streckenanschlag" / track stop collar) folds away to allow passing. It is being replaced by
ZBS until 2025.
*
Berlin U-Bahn small profile underground used a metal stick as a trip arm, which hung over the track horizontally like a semaphore signal. The trip cock was on the roof of the first wagon (near the first door) almost looking like a lightning rod. The system was phrased out in the 1960s (West) and 1990s (East).
*
Berlin U-Bahn large profile underground used a mushroom-shaped swivel next to the right rail as a trip arm. The trip cock was mounted on the first bogie. This system was replaced similarly.
*
London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
uses a square-shaped metal plate that functions similarly to that on the New York City Subway system.
* Several lines on the
Moscow Metro
The Moscow Metro) is a metro system serving the Russian capital of Moscow as well as the neighbouring cities of Krasnogorsk, Reutov, Lyubertsy and Kotelniki in Moscow Oblast. Opened in 1935 with one line and 13 stations, it was the first unde ...
use a semi-circle that rotates into position when signals are red. All of them are on the right side of tracks as trains' trip cocks are fitted on the right side.
*
New York City Subway
The New York City Subway is a rapid transit system owned by the government of New York City and leased to the New York City Transit Authority, an affiliate agency of the state-run Metropolitan Transportation Authority (MTA). Opened on October 2 ...
uses a T-shaped metal bar rising from the floor as a trip arm; on the right side of the track for the
A Division (numbered trains) and left side for the
B Division B Division, Division B, or variant may refer to:
* ''B Division'' (New York City Subway)
* ''B Division'' (Irish League), association football
* ''Division B'' (Scottish Football League)
* ''Divizia B'' (Romanian Football League)
* Moldovan "B ...
(lettered trains). To allow trains to proceed it pivots down. A trip cock is mounted on the corner of the truck (bogie) of each car. The placement of the trip cock depends on the division the train runs on; some rolling stock is equipped with a trip cock on both sides. The train stop can be identified on the tracks because they are painted yellow for evidence if it has ever tripped a train.
*
Sydney
Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountain ...
now uses the London Underground type J trip arm called the JA, except that it is mirror-image mounted on the left hand side of the track instead of the right hand side. A nearly identical system is used in
Wellington
Wellington ( mi, Te Whanganui-a-Tara or ) is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the second-largest city in New Zealand by me ...
.
*
Toronto Subway
The Toronto subway is a rapid transit system serving Toronto and the neighbouring city of Vaughan in Ontario, Canada, operated by the Toronto Transit Commission (TTC). It is a multimodal transport, multimodal rail network consisting of three Pa ...
also uses a T-shaped metal bar that rises from the floor except it is always on the right side of the track for all rolling stock because the trip cock is placed on the right side for all rolling stock.
Reverse direction
When trains operate in the reverse direction, they may "back trip" on train stops applying to the normal direction, which is a nuisance. This may be avoided in one of three ways:
#In
Melbourne
Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...
the rear trip cock is raised, although this runs the risk of runaways from terminal stations at high elevations.
#In Sydney, the rear trip is always lowered, and trip arms in the opposite direction are "suppressed" so that they do not engage the rear trip cock. Trip cocks on intermediate cars, if any, are always raised.
#In New York, when the signalling system clears motion in one direction (on bi-directional track or through an
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 ...
), it will automatically drive the trip arms which apply to the other direction. This is necessary because trip cocks are located along the entire length of trains in New York, not just the lead car.
On the
London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
there are many train stops on the
Piccadilly line
The Piccadilly line is a deep-level London Underground line running from the north to the west of London. It has two branches, which split at Acton Town, and serves 53 stations. The line serves Heathrow Airport, and some of its stations are n ...
facing the opposite direction of travel. This is because they protect
engineer's trains that often travel in opposite direction during engineering works.
Proving
The mechanical trip arm is proved in the lowered position before the red light of its associated signal is extinguished. The trip arm is proved in the raised position before the track circuit following that signal is indicated as unoccupied. The proving switch detects the actual arm of the train stop, and breakage of that arm centres the switch neither depressed nor normal thus alerting operators to its failure.
Tripping past, and accidents
When the signalling fails, etc., it may be necessary to "trip past" a train stop in the danger position, in accordance with the rules. With the train now working "on sight" it is important to travel at a low speed. If low speed is not maintained, then accidents can occur, such as
*
Roseville collision, 1950
*
Berala train collision, 1952
*
Glenbrook rail accident
The Glenbrook rail accident occurred on 2 December 1999 at 8:22 am on a curve east of Glenbrook railway station on the CityRail network between Glenbrook and Lapstone, in the Blue Mountains of New South Wales, Australia. Seven passengers were ...
, 1999
Depiction
The car chase scene in the motion picture
''The French Connection'' shows a train stop being struck by a New York City elevated subway train as it approaches the train ahead of it on the same track. Although the moving train hits the train stop and begins to slow down, for the purposes of the film sequence, it was supposedly traveling too fast to reach a full stop before colliding with the train ahead.
See also
*
Automatic train protection
Automatic train protection (ATP) is a type of train protection system which continually checks that the speed of a train is compatible with the permitted speed allowed by signalling, including automatic stop at certain signal aspects. If it is ...
(ATP)
*
Automatic warning system
The Automatic Warning System (AWS) was introduced in the 1950s in the United Kingdom to provide a train driver with an audible warning and visual reminder that they were approaching a distant signal at caution.
Its operation was later extended t ...
- does not enforce a stop at a red signal
*
Cab signalling
Cab signaling is a railway safety system that communicates track status and condition information to the cab, crew compartment or driver's compartment of a locomotive, railcar or multiple unit. The information is continually updated giving an ...
*
Catch points
Catch points and trap points are types of turnout which act as railway safety devices. Both work by guiding railway carriages and trucks from a dangerous route onto a separate, safer track. Catch points are used to derail vehicles which are ou ...
*
Dead man's switch
A dead man's switch (see alternative names) is a switch that is designed to be activated or deactivated if the human operator becomes incapacitated, such as through death, loss of consciousness, or being bodily removed from control. Originally 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. ...
*
Indusi or
PZB - German train protection system
*
Moorgate control
The Moorgate tube crash occurred on 28 February 1975 at 8:46 am on the London Underground's Northern City Line; 43 people died and 74 were injured after a train failed to stop at the line's southern terminus, Moorgate station, and crashed ...
*
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 ...
*
Train Protection & Warning System The Train Protection & Warning System (TPWS) is a train protection system used throughout the British passenger main-line railway network, and in Victoria, Australia.
The British Rail Safety and Standards Board's definition is:
The purpose of TPW ...
(TPWS)
References
Further reading
*
* General Railway Signal Co. (June 1979). ''Elements of Railway Signaling''
{{Rail tracks
Train protection systems