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97-454: ACSES provides railway trains with positive enforcement of "civil" speed restrictions (those based on the physical characteristics of the line). The on-board components keep track of a train's position and continuously calculates a maximum safe braking curve for upcoming speed restrictions. If the train exceeds the safe braking curve then the brakes are automatically applied. Data regarding permanent speed restrictions and other information about

194-505: A data radio subsystem for communication with wayside systems. In the cab, the driver has a consolidated display which displays the train's ACSES target speed along with the cab signal speed and other useful operating information. Messages conveyed to and from locomotive and ground-based systems are made up of Advanced Train Control System (ATCS) encoded message frames. The system begins with passive transponders attached between

291-425: A locking bed is constructed, consisting of steel bars forming a grid. The levers that operate switches , derails , signals or other appliances are connected to the bars running in one direction. The bars are constructed so that if the function controlled by a given lever conflicts with that controlled by another lever, mechanical interference is set up in the cross locking between the two bars, in turn preventing

388-476: A blown hose), the train breaking in two and uncoupling air hoses, or the engineer moving the automatic brake valve to the emergency position, will cause an emergency brake application . On the other hand, a slow leak that gradually reduces brake pipe pressure to zero, something that might happen if the air compressor is inoperative and therefore not maintaining main reservoir pressure, will not cause an emergency brake application. Electro-pneumatic or EP brakes are

485-596: A broken air brake hose) causes the air brakes to engage unexpectedly. An example of this problem can be seen in the accident that caused the death of John Luther "Casey" Jones on 30 April 1900 on the Illinois Central Railroad main line at Vaughan, Mississippi . The modern air brake is not identical with the original airbrake as there have been slight changes in the design of the triple valve, which are not completely compatible between versions, and which must therefore be introduced in phases. However,

582-432: A control lever may be moved into a position which would release other levers, a signal must be received from the field element that it has actually moved into the position requested. The locking bed shown is for a GRS power interlocking machine. Interlockings effected purely electrically (sometimes referred to as all-electric ) consist of complex circuitry made up of relays in an arrangement of relay logic that ascertain

679-490: A dual circuit system, usually with each bogie (truck) having its own circuit. In order to design a system without the shortcomings of the straight air system, Westinghouse invented a system wherein each piece of railroad rolling stock was equipped with an air reservoir and a triple valve , also known as a control valve . Unlike the straight air system, the Westinghouse system uses a reduction in air pressure in

776-462: A host of other vital inputs—is accumulated by wayside encoders, such as a Safetran VIU-ACSES (see photo to the right), before being sent to the BCMs for transmission to locomotives. The ACSES system also supports the use of temporary fixed transponders to enforce temporary speed restrictions as an alternative or backup to using the wireless network. One transponder is placed a safe braking distance from

873-502: A long time a three-wire version of the electro-pneumatic brake, which gives up to seven levels of braking force. In North America , the Westinghouse Air Brake Company supplied high-speed control brake equipment for several post- World War II streamlined passenger trains. This was an electrically controlled overlay on conventional D-22 passenger and 24-RL locomotive brake equipment. On the conventional side,

970-489: A more favorable signal indication a Stop Release button must be engaged by the engineer before the brakes can be released. Due to several limitations of the ACSES system and various contingency operations, employees must still be familiar with all permanent and temporary speed restrictions. ACSES is meant to supplement rather than replace employees' knowledge and skills. The combination of continuous cab signals and ACSES meet

1067-433: A number of safeguards that are usually taken to prevent this sort of accident from happening. Railroads have strict government-approved procedures for testing the air brake systems when making up trains in a yard or picking up cars en route. These generally involve connecting the air brake hoses, charging up the brake system, setting the brakes and manually inspecting the cars to ensure the brakes are applied, and then releasing

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1164-404: A positive stop at any signal at the entrance to cab signal without fixed wayside signal territory that is not displaying "Clear to Next Interlocking." If a locomotive is unable to automatically retrieve temporary speed restriction information, permanent speed restrictions will continue to be enforced. In the event of a total failure of the on-board ACSES system the engineer may revert to the use of

1261-481: A real time braking curve. As the locomotive proceeds down the track, the on-board systems communicate via radio to the trackside BCMs (Base Communications Manager) in the region, requesting any temporary speed restrictions for the next three or more regions of the track, ensuring that the locomotive's database is always kept current with any possible temporary restrictions issued by the train dispatcher. Wayside Communications Managers (WCM) (or packet switches ) link all

1358-460: A total of 1,864 interlocking levers, were in use on 13 North American railroads. This type of system would remain one of two viable competing systems into the future, although it did have the disadvantage of needing extra single-use equipment and requiring high maintenance. Interlockings using electric motors for moving switches and signals became viable in 1894, when Siemens in Austria installed

1455-805: A type of air brake that allows for immediate application of brakes throughout the train instead of the sequential application. EP brakes have been in British practice since 1949 and also used in German high-speed trains (most notably the ICE ) since the late 1980s; they are fully described in Electro-pneumatic brake system on British railway trains . As of 2005 , electro-pneumatic brakes were in testing in North America and South Africa on captive service ore and coal trains. Passenger trains have had for

1552-410: Is a little simpler than the air brake. Instead of an air compressor, steam engines have an ejector with no moving parts, and diesel or electric locomotives have a mechanical or electrical "exhauster". Disconnection taps at the ends of cars are not required because the loose hoses are sucked onto a mounting block. However, the maximum pressure in a vacuum system is limited to atmospheric pressure, so all

1649-417: Is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. In North America, a set of signalling appliances and tracks interlocked together are sometimes collectively referred to as an interlocking plant or just as an interlocking . An interlocking system is designed so that it is impossible to display a signal to proceed unless

1746-403: Is an indication that the cars' triple valves are malfunctioning. Depending on the location of the air test, the repair facilities available, and regulations governing the number of inoperative brakes permitted in a train, the car may be set out for repair or taken to the next terminal where it can be repaired. A different kind of accident can occur if a malfunction in the air brake system (such as

1843-472: Is based on and aligned with UIC Leaflet 540, a document ratified by many train-operating companies. UIC Leaflet 540 explicitly approves the following brake systems: Historically, and according to UIC 540, we distinguish systems technically approved since 1927-1932 such as: Westinghouse W , Knorr K , Kunze-Knorr , Drolshammer, Bozic, Hildebrand-Knorr. In the steam era, Britain's railways were divided–some using vacuum brakes and some using air brakes–but there

1940-416: Is closed, allowing the train line to be recharged by the compressor of the locomotive. The subsequent increase of train line pressure causes the triple valves on each car to discharge the contents of the brake cylinder to the atmosphere, releasing the brakes and recharging the reservoirs. The Westinghouse system is thus fail-safe —any failure in the train line, including a separation ("break-in-two") of

2037-461: Is divided into two portions: the service section, which contains the mechanism used during brake applications made during service reductions, and the emergency section, which senses the faster emergency reduction of train line pressure. In addition, each car's air brake reservoir is divided into two sections—the service portion and the emergency portion—and is known as the "dual-compartment reservoir”. Normal service applications transfer air pressure from

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2134-458: Is where the locomotive's air compressor output is stored and is ultimately the source of compressed air for all connected systems. Since the main reservoir pipe is kept constantly pressurized by the locomotive, the car reservoirs can be charged independently of the brake pipe, this being accomplished via a check valve to prevent backfeeding into the pipe. This arrangement helps to reduce the above-described pressure loss problems, and also reduces

2231-598: The 1953 Pennsylvania Railroad train wreck involving the Federal Express , a Pennsylvania Railroad passenger train which became a runaway while heading into Washington Union Station in Washington, D.C. , causing the train to crash into the passenger concourse and fall through the floor. Similarly, in the Gare de Lyon rail accident , a valve was accidentally closed by the crew, reducing braking power. There are

2328-719: The London and North Western Railway alone. The first experiment with mechanical interlocking in the United States took place in 1875 by J. M. Toucey and William Buchanan at Spuyten Duyvil Junction in New York on the New York Central and Hudson River Railroad (NYC&HRR). At the time, Toucey was General Superintendent and Buchanan was Superintendent of Machinery on the NYC&;HRR. Toucey and Buchanan formed

2425-408: The permanent way and track configuration is obtained in chunks from the track mounted transponders and stored in an onboard database. Information regarding temporary speed restrictions is given to the train while en route via a wireless data system. The on-board equipment tracks the train's position by counting wheel rotations between the transponders, which also serve as fixed location references. In

2522-411: The rate of brake pipe pressure reduction. Therefore, as long as a sufficient volume of air can be rapidly vented from the brake pipe, each car's triple valve will cause an emergency brake application. However, if the brake pipe pressure is too low due to an excessive number of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving

2619-421: The 1980s when solid state interlocking and control systems began to replace the older relay plants of all types. Modern interlockings (those installed since the late 1980s) are generally solid state , where the wired networks of relays are replaced by software logic running on special-purpose control hardware. The fact that the logic is implemented by software rather than hard-wired circuitry greatly facilitates

2716-411: The ACSES cab display unit, which then enforces the more restrictive of the two speeds. The on-board ACSES unit is backward compatible and can function where only the cab signaling is present without the ACSES overlay as well of situations where ACSES is available without cab signals. ACSES also enforces a positive stop at signals displaying an absolute Stop indication. The transponder information allows

2813-492: The BCMs in the region to a backhaul network which allows them to communicate with the dispatcher's office and associated control systems via TCP/IP. This design provides locomotives with information about speed restrictions as soon as they go into effect without having to rely on voice communications with the train crew. Additional BCMs (data radios) located at interlockings transmit information relating to absolute Stop signal indications and any speed restrictions pertaining to

2910-705: The Toucey and Buchanan Interlocking Switch and Signal Company in Harrisburg, Pennsylvania in 1878. The first important installations of their mechanism were on the switches and signals of the Manhattan Elevated Railroad Company and the New York Elevated Railroad Company in 1877–78. Compared to Saxby's design, Toucey and Buchanans' interlocking mechanism was more cumbersome and less sophisticated, and so

3007-515: The ability to make modifications when needed by reprogramming rather than rewiring. In many implementations, this vital logic is stored as firmware or in ROM that cannot be easily altered to both resist unsafe modification and meet regulatory safety testing requirements. As display technology improved, the hard wired physical devices could be updated with visual display units (computer monitors), which allowed changes in field equipment be represented to

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3104-455: The air brake's simplest form, called the straight air system , compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow the train. The mechanical linkage can become quite elaborate, as it evenly distributes force from one pressurized air cylinder to 8 or 12 wheels. The pressurized air comes from an air compressor in

3201-410: The air from the train line and vent the coupling hoses for uncoupling cars. The air brake only operates if the angle cocks are open except the ones at the front of the locomotive and at the end of the train. The air brake can fail if one of the angle cocks is accidentally closed. In this case, the brakes on the wagons behind the closed cock will fail to respond to the driver's command. This happened in

3298-466: The basic air brakes used on railways worldwide are remarkably compatible. European brake systems vary between countries, but the working principle is the same as for the Westinghouse air brake. European passenger cars used on national railway networks must comply with TSI LOC&PAS regulation, which specifies in section 4.2.4.3 that all brake systems must adhere to the EN 14198:2004 standard. This standard

3395-422: The brake pipe pressure to reduce and consequently takes several seconds for the brakes to apply throughout the train. The speed of pressure changes during a service reduction is limited by the compressed air's ability to overcome the flow resistance of the relatively-small-diameter pipe and numerous elbows throughout the length of the train, and the relatively-small exhaust port on the head-end locomotive, which means

3492-401: The brake pipe's pressure directly to atmosphere. This serves to more rapidly vent the brake pipe and hasten the propagation of the emergency reduction rate along the entire length of the train. Use of distributed power (i.e., remotely controlled locomotive units mid-train and/or at the rear end) somewhat mitigates the time-lag problem with long trains, because a telemetered radio signal from

3589-573: The brake pipe, the rate of reduction is highest near the front of the train (in the case of an engine operator-initiated emergency application) or near the break in the brake pipe (in the case of loss of brake pipe integrity). Farther away from the source of the emergency application, the rate of reduction can be reduced to the point where triple valves will not detect the application as an emergency reduction. To prevent this, each triple valve's emergency portion contains an auxiliary vent port, which, when activated by an emergency application, also locally vents

3686-411: The brakes and manually inspecting the cars to ensure the brakes are released. Particular attention is usually paid to the rearmost car of the train, either by manual inspection or via an automated end-of-train device , to ensure that brake pipe continuity exists throughout the entire train. When brake pipe continuity exists throughout the train, failure of the brakes to apply or release on one or more cars

3783-508: The brakes must be applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort, as the system is starting out at a lower point of equilibrium (lower overall pressure). If many brake pipe reductions are made in short succession ("fanning the brake" in railroad slang), a point may be reached where car reservoir pressure will be severely depleted, resulting in substantially reduced brake cylinder piston force, causing

3880-426: The brakes of the rear-most cars will apply sometime after those of the forward-most cars apply, so some slack run-in can be expected. The gradual reduction in brake pipe pressure will mitigate this effect. Modern locomotives employ two air brake systems. The system which controls the brake pipe is called the automatic brake and provides service and emergency braking control for the entire train. The locomotive(s) at

3977-425: The brakes to fail. On a descending grade , the result will be a runaway. In the event of a loss of braking due to reservoir depletion, the engine driver may be able to regain control with an emergency brake application, as the emergency portion of each car's dual-compartment reservoir should be fully charged—it is not affected by normal service reductions. The triple valves detect an emergency reduction based on

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4074-507: The cab signal system without civil speed enforcement. Both situations require permission to be obtained from the train dispatcher and are accompanied by additional maximum speed restrictions. At interlockings where the Data Radio (BCM) is either not installed or not functioning, the train will determine if a positive stop is necessary via the cab signaling system. If it is necessary to pass a signal at Stop after receiving authorization from

4171-445: The conflicting lever movement from being made. In purely mechanical plants, the levers operate the field devices, such as signals, directly via a mechanical rodding or wire connection. The levers are about shoulder height since they must supply a mechanical advantage for the operator. Cross locking of levers was effected such that the extra leverage could not defeat the locking (preliminary latch lock). The first mechanical interlocking

4268-466: The control valve set a reference pressure in a volume, which set brake cylinder pressure via a relay valve. On the electric side, pressure from a second straight-air trainline controlled the relay valve via a two-way check valve. This "straight air" trainline was charged (from reservoirs on each car) and released by magnet valves on each car, controlled electrically by a three-wire trainline, in turn controlled by an electro-pneumatic master controller in

4365-423: The controlling locomotive. This controller compared the pressure in the straight air trainline with that supplied by a self-lapping portion of the engineers valve, signaling all of the "apply" or "release" magnets valves in the train to open simultaneously, changing the pressure in the straight-air trainline much more rapidly and evenly than possible by simply supplying air directly from the locomotive. The relay valve

4462-406: The definition of a positive train control (PTC) system by providing collision protection, enforcement of all speed restrictions and enforcement of track possession by maintenance forces. The on-board equipment consists of a computer that also stores the route characteristics database, a distance measurement subsystem to track train position, an antenna subsystem for the track mounted balises , and

4559-583: The design, and little saving of labour was achieved. The inventors of the hydro-pneumatic system moved forward to an electro-pneumatic system in 1891 and this system, best identified with the Union Switch & Signal Company, was first installed on the Chicago and Northern Pacific Railroad at its drawbridge across the Chicago River . By 1900, 54 electro-pneumatic interlocking plants, controlling

4656-524: The dispatcher, ACSES will limit the train to 15 miles per hour (24 km/h) within the interlocking limits after use of the Stop Release button. Railway air brake A railway air brake is a railway brake power braking system with compressed air as the operating medium. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on April 13, 1869. The Westinghouse Air Brake Company

4753-419: The engine driver with no means to stop the train. To prevent a runaway due to loss of brake pressure, dynamic (rheostatic) braking can be utilized so the locomotive(s) will assist in retarding the train. Often, blended braking , the simultaneous application of dynamic and train brakes, will be used to maintain a safe speed and keep the slack bunched on descending grades. Care would then be given when releasing

4850-441: The engine operator can make an "emergency application," which will rapidly vent all of the brake pipe pressure to atmosphere, resulting in a faster application of the train's brakes. An emergency application also results when the integrity of the brake pipe is lost, as all air will also be immediately vented to atmosphere. An emergency brake application brings in an additional component of each car's air brake system. The triple valve

4947-416: The engine operator in the front locomotive commands the distant units to initiate brake pressure reductions that propagate quickly through nearby cars. Many modern air brake systems use distributors instead of triple valves. These serve the same function as triple valves, but have additional functionality such as the ability to partially release the brakes. The locomotive's air compressor typically charges

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5044-416: The engineer moves the automatic brake handle to a "service" position, which causes a reduction in brake pipe pressure. During normal service, the pressure in the brake pipe is never reduced to zero and in fact, the smallest reduction that will cause a satisfactory brake response is used to conserve brake pipe pressure. A sudden and substantial pressure reduction caused by a loss of brake pipe integrity (e.g.,

5141-400: The equipment has to be much larger and heavier to compensate. That disadvantage is made worse at high altitude. The vacuum brake is also considerably slower to both apply and release the brake, which requires a greater level of skill and anticipation from the driver. Conversely, the vacuum brake originally had the advantage of allowing gradual release, whereas the Westinghouse automatic air brake

5238-415: The event a train's crew exceeds a speed restriction a penalty brake application is applied bringing the train to a complete stop in the same fashion as existing automatic train control (ATC) systems. Speed restrictions required by the signal system are provided by the legacy Pulse code cab signaling system, which has been in service on various railroads since the 1930s. The cab signal codes are fed into

5335-973: The first such interlocking at Přerov (now in the Czech Republic). Another interlocking of this type was installed in Westend near Berlin in 1896. In North America, the first installation of an interlocking plant using electric switch machines was at Eau Claire, Wisconsin on the Chicago, St. Paul, Minneapolis and Omaha Railway in 1901, by General Railway Signal Company (GRS, now a unit of Alstom , headquartered in Levallois-Perret , near Paris). By 1913, this type system had been installed on 83 railroads across 35 US states and Canadian provinces, in 440 interlocking plants using 21,370 levers. Interlockings can be categorized as mechanical, electrical (electro-mechanical or relay -based), or electronic/ computer-based . In mechanical interlocking plants,

5432-540: The fundamental principles of interlocking include: Railway interlocking is of British origin, where numerous patents were granted. In June 1856, John Saxby received the first patent for interlocking switches and signals. In 1868, Saxby (of Saxby & Farmer) was awarded a patent for what is known today in North America as “preliminary latch locking”. Preliminary latch locking became so successful that by 1873, 13,000 mechanical locking levers were employed on

5529-403: The head of the train (the "lead consist") have a secondary system called the independent brake. The independent brake is a "straight air" system that makes brake applications on the head-of-train locomotive consist independently of the automatic brake, providing for more nuanced train control. The two braking systems may interact differently as a matter of preference by the locomotive builder or

5626-761: The interlocking plant. The first NX installation was in 1937 at Brunswick on the Cheshire Lines , UK. The first US installation was on the New York Central Railroad (NYCRR) at Girard Junction, Ohio in 1937. Another NYCRR installation was on the main line between Utica, New York and Rochester, New York , and this was quickly followed up by three installations on the New York City Subway 's IND Fulton Street Line in 1948. Other NX style systems were implemented by other railroad signal providers. For example, Union Route (UR)

5723-445: The large mechanical levers of previous systems being replaced by buttons, switches or toggles on a panel or video interface. Such an interlocking may also be designed to operate without a human operator. These arrangements are termed automatic interlockings , and the approach of a train sets its own route automatically, provided no conflicting movements are in progress. GRS manufactured the first all-relay interlocking system in 1929. It

5820-411: The locomotive and is sent from car to car by a train line made up of pipes beneath each car and hoses between cars. The principal problem with the straight air braking system is that any separation between hoses and pipes causes loss of air pressure and hence the loss of the force applying the brakes. This could easily cause a runaway train . Straight air brakes are still used on locomotives, although as

5917-524: The locomotive. As a locomotive moves from region to region, the radio signal strengths are recorded by BCMs which get conveyed to the WCMs change. BCMs which fall out of range of locomotives are removed from talk path routes within the WCM in favor of the BCMs which are coming into range. In this way the WCM is constantly aware of where each locomotive is located and which talk path is best used to communicate with

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6014-436: The locomotive. Such information is also conveyed to the office so that office systems may make use of it. In the event of a loss of all redundant standby systems (such as might occur due to a wide area power failure or communications failure with the central office) the system will indicate to the locomotive engineer that it has lost the ability to enforce temporary speed restrictions, but the permanent restrictions loaded into

6111-460: The main reservoir with air at 125–140 psi (8.6–9.7 bar; 860–970 kPa). The train brakes are released by admitting reduced and regulated main reservoir air pressure to the brake pipe through the engineer's automatic brake valve. In America, a fully charged brake pipe typically operates at 90 psi (6.2 bar; 620 kPa) for freight trains and 110 psi (7.6 bar; 760 kPa) for passenger trains. The brakes are applied when

6208-422: The office systems. Because a locomotive's radio is capable of being heard by a number of BCMs, the WCM examines the indication RF signal strength of each BCM that heard the locomotive to determine what the strongest talk path back to the locomotive is. The WCM maintains a record of three possible talk paths to the locomotive such that the strongest path is always selected if the office needs to communicate back to

6305-500: The on-board database will continue to be enforced. Finally, the cab signals are considered a completely independent system that transmits a continuous stream of codes through the rails instead of via wireless transmission. Any fault in the ACSES overlay will not affect the cab signal system and moreover a cab signal failure will not affect the ACSES system. Without cab signals ACSES will continue to enforce positive stops at absolute signals, all permanent and temporary speed restrictions and

6402-418: The piston valve, the slide valve, and the graduating valve. When the engine operator applies the brake by operating the locomotive brake valve, the train line vents to atmosphere at a controlled rate, reducing the train line pressure and in turn triggering the triple valve on each car to feed air into its brake cylinder. When the engine operator releases the brake, the locomotive brake valve portal to atmosphere

6499-404: The railroad. In some systems, the automatic and independent applications will be additive; in some systems the greater of the two will apply to the locomotive consist. The independent system also provides a bail off mechanism, which releases the brakes on the lead locomotives without affecting the brake application on the rest of the train. In the event the train needs to make an emergency stop,

6596-406: The release). In his patent application, Westinghouse refers to his 'triple-valve device' because of the three component valvular parts comprising it: the diaphragm-operated poppet valve feeding reservoir air to the brake cylinder, the reservoir charging valve, and the brake cylinder release valve. Westinghouse soon improved the device by removing the poppet valve action. These three components became

6693-435: The reporting back of performance of each wagon's brakes. The Westinghouse air brake system is very reliable but not infallible. The car reservoirs recharge only when the brake pipe pressure is higher than the reservoir pressure. Fully recharging the reservoirs on a long train can require considerable time (8 to 10 minutes in some cases ), during which the brake pipe pressure will be lower than locomotive reservoir pressure. If

6790-414: The response is conveyed back to the locomotive which updates its local database with any restrictions. There are a number of redundant components in the overall ACSES system such that a failure of a subsystem will swap over to another automatically. The loss of a WCM, for example, due to a power outage or lightning strike results in a standby WCM taking over the communications duties between BCMs and

6887-403: The route manually. The NX system allowed an operator looking at the diagram of a complicated junction to simply push a button on the known entrance track and another button on the desired exit track. The logic circuitry handled all the necessary actions of commanding the underlying relay interlocking to set signals and throw switches in the proper sequence, as required to provide valid route through

6984-761: The route to be used is proven safe. Interlocking is a safety measure designed to prevent signals and points/switches from being changed in an improper sequence. For example, interlocking would prevent a signal from being changed to indicate a diverging route, unless the corresponding points/switches had been changed first. In North America, the official railroad definition of interlocking is: " An arrangement of signals and signal appliances so interconnected that their movements must succeed each other in proper sequence ". A minimal interlocking consists of signals , but usually includes additional appliances such as points and Facing Point locks (US: switches) and derails , and may include crossings at grade and movable bridges. Some of

7081-447: The service and dynamic brakes to prevent draw-gear damage caused by a sudden run out of the train's slack. Another solution to loss of brake pressure is the two-pipe system, fitted on most locomotive-hauled passenger stock and many freight wagons. In addition to the traditional brake pipe, this enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive's main reservoir. The main reservoir

7178-413: The service section to the brake cylinder, while emergency applications cause the triple valve to direct all air in both the sections of the dual-compartment reservoir to the brake cylinder, resulting in a 20 to 30 percent stronger application. The emergency portion of each triple valve is activated by the higher rate of reduction of brake pipe pressure. Due to the length of trains and the small diameter of

7275-665: The signal industry was achieving the same level of safety and reliability that was inherent to purely mechanical systems. An experimental hydro-pneumatic interlocking was installed at the Bound Brook, New Jersey junction of the Philadelphia and Reading Railroad and the Lehigh Valley Railroad in 1884. By 1891, there were 18 hydro-pneumatic plants, on six railroads, operating a total of 482 levers. The installations worked, but there were serious defects in

7372-828: The signaller without any hardware modifications. " Solid State Interlocking " (SSI) is the brand name in trade of work of the first generation microprocessor -based interlocking developed in the 1980s by British Rail , GEC-General Signal and Westinghouse Signals Ltd in the UK. Second generation processor-based interlockings are known by the term "Computer Based Interlocking" (CBI), of which VPI (trademark of General Railway Signal , now Alstom), MicroLok (trademark of Union Switch & Signal , now Hitachi Rail STS ), Westlock and Westrace (trademarks of Invensys Rail , now Siemens), and [Smartlock ] (trademark of Alstom ), and EBI Lock (trademark of Bombardier ) are examples. Interlockings allow trains to cross from one track to another using

7469-410: The start of the restriction to engage it, and a second is placed at the end to release it. In the office where dispatch and control is performed, a system provides a visual indication of the current status of communications with all locomotives as well as a close approximation of where each locomotive is currently located along the track. In the event that maintenance is needed along any section of

7566-505: The state or position of each signal appliance. As appliances are operated, their change of position opens some circuits that lock out other appliances that would conflict with the new position. Similarly, other circuits are closed when the appliances they control become safe to operate. Equipment used for railroad signalling tends to be expensive because of its specialized nature and fail-safe design. Interlockings operated solely by electrical circuitry may be operated locally or remotely, with

7663-496: The system were not dependent on each other in any way, and any or all of these options could be supplied separately. Later systems replace the automatic air brake with an electrical wire which runs in a circle round the whole train and has to be kept energized to keep the brakes off. In the UK it is known as a train wire . It is routed through various "governors" (switches operated by air pressure) which monitor critical components such as compressors, brake pipes and air reservoirs. If

7760-413: The time required for the brakes to release, since the brake pipe only has to recharge itself. Main reservoir pipe pressure can also be used to supply air for auxiliary systems such as pneumatic door operators or air suspension. Nearly all passenger trains (all in the UK and USA), and many freights, now have the two-pipe system. At both ends of each car, there are angle cocks fitted. These valves cut off

7857-467: The track, before a work crew is dispatched or before a work crew is granted authority to proceed, a temporary speed restriction (TSR) is created in the office computer systems. After a series of verifications and procedures, the TSR is presented to the ACSES office system. When a locomotive issues a query for TSRs for a given region, the WCM conveys the request for information to the office system via TCP/IP and

7954-491: The tracks which are electrically powered by an electromagnetic field when a locomotive passes over them. The transponders digitally convey their identification information and other relevant bits of information wirelessly via an onboard antenna, allowing the locomotives to know precisely when they have reached a particular waypoint . This location information is utilized by the on-board systems when consulting its database of speed restrictions and track characteristics to calculate

8051-412: The train divides, the wire will be broken, ensuring that all motors are switched off and both portions of the train have an immediate emergency brake application . More recent innovations are electronically controlled pneumatic brakes where the brakes of all the wagons (cars) and locomotives are connected by a kind of local area network , which allows individual control of the brakes on each wagon, and

8148-399: The train line to indirectly apply the brakes. The triple valve is so named because it performs three functions: It allows air into an air tank ready to be used, it applies the brakes, and it releases them. In so doing, it supports certain other actions (i.e. it 'holds' or maintains the application and it permits the exhaust of brake cylinder pressure and the recharging of the reservoir during

8245-422: The train to keep track of when it is approaching an absolute signal and then determine if a positive stop is required depending on cab signal indication and information provided via a local data radio. The system is calibrated to stop the train somewhere within the "Positive Stop Zone", which extends up to 1000 feet from the absolute stop signal itself. To pass the stop signal or otherwise move the train in absence of

8342-437: The train's route through said interlocking. Speed information acquired in this fashion will be displayed on the ACSES speed readout to supplement any speed information provided by the cab signaling system. After a positive stop the data radios will also transmit information releasing the train from the stop when track conditions permit. Such information about the status of the track occupancy, switch position, signal indication, and

8439-442: The train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop, thus preventing a runaway train. Modern air brake systems serve two functions: When the train brakes are applied during normal operation, the engine operator makes a "service application" or a "service rate reduction”, which means that the brake pipe pressure reduces at a controlled rate. It takes several seconds for

8536-415: The vacuum. Electro-vacuum brakes have been used with considerable success on South African electric multiple unit trains. Despite requiring larger and heavier equipment, as stated above, the performance of the electro-vacuum brake approached that of contemporary electro-pneumatic brakes. However, their use has not been repeated. Information Interlocking In railway signalling , an interlocking

8633-462: Was a gradual standardization on the vacuum brake. Some locomotives, e.g. on the London, Brighton and South Coast Railway , were dual-fitted so that they could work with either vacuum- or air-braked trains. In the diesel era, the process was reversed and British Railways switched from vacuum-braked to air-braked rolling stock in the 1960s. The main competitor to the air brake is the vacuum brake, which operates on negative pressure. The vacuum brake

8730-430: Was condensed into a single large power signal box with a control panel in the operator's area and the equivalent of a telephone exchange in the floors below that combined the vital relay based interlocking logic and non-vital control logic in one place. Such advanced schemes would also include train describer and train tracking technologies. Away from complex terminals unit lever control systems remained popular until

8827-563: Was equipped with four diaphragms, magnet valves, electric control equipment, and an axle-mounted speed sensor, so that at speeds over 60 mph (97 km/h) full braking force was applied, and reduced in steps at 60, 40 and 20 mph (97, 64 and 32 km/h), bringing the train to a gentle stop. Each axle was also equipped with anti-lock brake equipment. The combination minimized braking distances, allowing more full-speed running between stops. The straight-air (electro-pneumatic trainline) , anti-lock, and speed graduating portions of

8924-583: Was installed in Lincoln, Nebraska on the Chicago, Burlington and Quincy Railroad . Entrance-Exit Interlocking (NX) was the original brand name of the first generation relay-based centralized traffic control (CTC) interlocking system introduced in 1936 by GRS (represented in Europe by Metropolitan-Vickers ). The advent of all electric interlocking technology allowed for more automated route setting procedures as opposed to having an operator line each part of

9021-441: Was installed in 1843 at Bricklayers Arms Junction , England. Power interlockings may also use mechanical locking to ensure the proper sequencing of levers, but the levers are considerably smaller as they themselves do not directly control the field devices. If the lever is free to move based on the locking bed, contacts on the levers actuate the switches and signals which are operated electrically or electro- pneumatically . Before

9118-428: Was not implemented very widely. Union Switch & Signal bought their company in 1882. As technology advanced the railway signaling industry looked to incorporate these new technologies into interlockings to increase the speed of route setting, the number of appliances controlled from a single point and to expand the distance that those same appliances could be operated from the point of control. The challenge facing

9215-437: Was originally available in only the direct-release form still common in freight service. A primary fault of vacuum brakes is the inability to find leaks easily. In a positive air system, a leak is quickly found due to the escaping pressurized air. Discovering a vacuum leak is more difficult, although it is easier to repair, because a piece of rubber (for example) can just be tied around the leak and will be firmly held in place by

9312-423: Was subsequently organized to manufacture and sell Westinghouse's invention. In various forms, it has been nearly universally adopted. The Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure causes each car to release the brakes. A subsequent reduction or loss of air pressure causes each car to apply its brakes, using the compressed air stored in its reservoirs. In

9409-408: Was the brand name of their Entrance-Exit system supplied by Union Switch & Signal Co. (US&S), and introduced in 1951. NX type systems and their costly pre-solid state control logic only tended to be installed in the busier or more complicated terminal areas where it could increase capacity and reduce staffing requirements. In a move that was popular in Europe, the signalling for an entire area

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