Train working systems – I
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General information on signalling and train working
Q. What kinds of signalling and train working systems are in use in India?
[4/00] The absolute block system is the most widespread method of train working on IR. The block sections may be handled manually or automatically, or by some combination of those. Some sections still use different forms of physical token systems such as the Neale's Ball Token instruments.
Other than the block system some other special-purpose methods of train working are used in some circumstances. There are many old and new kinds of signalling systems used by IR. Many regions use lower-quadrant or upper-quadrant semaphore signalling (now with electric lamps for night operation, but formerly using oil lamps). Many routes have been fitted with (automatic or manual, 2-, 3- or 4-aspect) colour-light signal systems that are electrically operated.
Apart from these FAQ pages, some extracts of the IR General Rules on train working are also available.
AWS (Automatic Warning System), an in-cab signal warning system, is in place on many main lines, including New Delhi - Mughalsarai, parts of New Delhi - Bombay, New Delhi - Agra. etc. A few areas have seen the introduction of forms of centralized traffic control (CTC) in conjunction with automatic colour-light signalling. (CTC was first introduced on the NER's busy MG section between Gorakhpur and Chupra, and later on the Bongaigaon-Changsari section of NFR.) The suburban section of Madras Egmore - Tambaram also has CTC.
Busy urban areas have electronic interconnections among the signal systems of the stations within the areas. Suburban systems generally have colour-light signalling and automatic block systems, sometimes with AWS or some form of automatic train stop systems (ATP, automatic train protection) as well. Automatic train stop systems were tried on some main lines in the 1960's but were given up following excessive vandalism and pilferage of equipment and maintenance problems.
A Train Management System (TMS), from Bombardier, is used on the Mumbai suburban system (Churchgate - Virar) which provides centralized online monitoring of train positions. The Delhi Metro system uses Continuous ATC (CATC) including ATS and ATP on all its sections. Its metro (underground) section uses a flavour of ATO. Drivers are still on board each train on the underground section, but under normal conditions they don't do much beyond handling the door opening and closing. All normal operations of running the trains -- accelerating them, braking them, etc., are handled by the ATO system, with speeds up to 80km/h. The ATO system was supplied by Alstom (France)..
Around Chennai, several suburban stations have their signals automatically controllable from Basin Bridge using a fault-tolerant system that interconnects the signalling of up to 32 stations using a dual fibre-optic ring. This system also provides for 6 voice channels for communication among these stations. This system was developed indigenously by SR, the Dept. of Electronics, and IIT Madras.
Points and interlockings may be worked mechanically (rod or pipe linkages are common, but earlier, double-wire systems were also used) or electrically (motor driven). Many points exist which have to be manually operated at the location of the points after using a key to unlock the points.
Following British practice, IR's signalling is essentially route signalling where the signals generally indicate which route has been set for a train, letting the driver choose the speed as appropriate for the divergences, curves, etc. (as opposed to speed signalling which is the basic philosophy underlying American practice). Of course no modern system of signalling is purely route-based or speed-based, and there are elements of speed signalling in some of IR's signalling as well.
To give a sense of the variety of systems in use, here is a sample [6/99]:
- Mumbai CSTM - Badlapur : Automatic Multiple Aspect Colour Light Signals
- Badlapur - Pune - Daund : Manually controlled Multiple Aspect Colour Light Signals
- Daund - Manmad : Lower Quadrant Semaphore signals
- Daund - Solapur: Some stretches of Multiple Aspect Colour Light Signals and some sections of Tokenless Upper quadrant semaphore
- Pune - Miraj - Kolhapur : Neale's ball token instrument
- Batala - Qadian, Garhi Harsuru - Farukhnagar : One Train Only system
- Tilwara - Tilwara Mela : Train Staff and Ticket system
Q. What's 'interlocking'?
In order to ensure that the signalling system never provides unsafe (conflicting) signals and the points are not set for more than one train that might end up proceeding on to the same section of track and hence suffering a collision, various schemes have been developed to coordinate the settings of the points and the signals within the region controlled by a signalbox or signal cabin.
Mechanically operated interlocking
The most prevalent systems today [2003] are still mechanical interlocking schemes that coordinate the positions of the levers controlling the points with the signals governing that section of track and connected branches, loops, or sidings.
For instance, in one common scheme, a key that allows setting the points for a route has to be obtained from the block instrument, and as long as the key is removed the instrument cannot be set to provide Line Clear for a conflicting route. The wires that operate signals, and the rods that control points, are all interconnected in the lever frames at the signal cabins so that they are literally 'interlocked' -- the position of one lever or key physically obstructs the movements of other levers and keys which control points or signals that can be set in conflicting ways.
Manually operated interlocking
This is a form of mechanical interlocking as well, but relies on the signalman to move about from one set of points and signals to another carrying with him the keys used to operate them. At small stations and on less busy branch lines various forms of manually operated mechanical interlocking are still [11/03] widespread. At points controlling catch sidings in hilly areas, often the interlocking is manual where the driver has to use a key provided by the stationmaster or signalman of the last station before the siding -- the key is inserted into the interlock box which notifies the signal cabin and the points are then set for the main line and the signal is pulled off, giving the train authority to proceed. (This system is common in many hilly areas, although busier lines with catch sidings are being provided with automatically operating delayed signals where the points are controlled by a timer and are set to the main line only after the train has halted for the prescribed period of time.)
Even as of the late 1980s one had only to go a few kilometers outside any big city along a railway line to spot tiny signal cabins or block huts along quiet lines where all the action was done by the signalman unlocking and locking points and pulling off signals after talking on the magneto-telephone to his counterpart at the next signal ahead.
Hepper's Key Instruments and similar key dispensing instruments were and probably still are in wide use for operating points manually. Depending on the state of the block instrument and the interlocking set up for the local layout of lines, these instruments would dispense a key only when the appropriate combination of signals had been set; the key would then be used to unlock points to divert a train on to a loop, for instance -- and while the points were so set, that key would not be released and the signals could not be changed
A common system in use was Sequential Key Interlocking, which saved on the installation of point rodding and instead relied on the signalman walking over with a key to lock or unlock points. As an example, consider a station with a main line and a loop line. To receive a train on the main line, a key is inserted into the signal frame in the cabin or platform, which allows the Outer and Home signals of the station to be pulled off.
In order to receive a train on the loop line instead, the key is used as before to pull off the Outer signal, but the Home is kept at danger. Instead, when the train has stopped at the Home signal the key is removed and taken to the facing points for the loop. The same key unlocks the points so they can be set for the loop; it also releases another key which has to be taken back and inserted in the signal frame at the platform to pull off the Home signal to let the train advance on to the loop.
The mechanism was such that only one of these two keys could be released at once; the second key did not allow the operation of the Outer signal, and it had to be taken back to the facing points of the loop in order to release the first key.
Electrically operated interlocking
In the more advanced electrical or electronic interlocking schemes, the points and signals are worked from one integrated mechanism in a signal cabin which features a display of the entire track layout with indications of sections that are occupied, free, set for reception or dispatch, etc. The interlocking is accomplished not by mechanical devices but by electrical circuitry -- relays and switches in older electrical or electropneumatic systems, and computerized circuits in the newer electronic systems.
Panel Interlocking (PI) is the system used in most medium-sized stations on IR. In this, the points and signals are worked by individual switches that control them. Route Relay Interlocking (RRI) is the system used in large and busy stations that have to handle high volumes of train movements. In this, an entire route through the station can be selected and all the associated points and signals along the route can be set at once by a switch for receiving, holding, blocking, or dispatching trains.
As an example, Old Delhi station has an RRI system from Siemens which allows selection from among 1122 possible routes. CR has a large RRI system at Kurla which controls signals from Ghatkopar to Sion on the Main Line, at Lokmanya Tilak Terminus, and from Chembur to GTB Nagar on the Harbour Line. The first route-relay interlocking system was set up on WR at Churchgate station control tower in the 1950s (equipment from Siemens?).
Currently [10/04], the numbers of stations with some form of electronic interlocking systems are: 18 on CR, 195 on ER, 263 on NR, 22 on NER, 43 on NFR, 55 on SR, 101 on SCR, 132 on SER, 44 on WR, 130 on ECR, 99 on ECoR, 154 on NCR, 13 on NWR, 71 on SECR, 34 on SWR, and 76 on WCR.
Regardless of whether the mechanisms are controlled manually or by electronic circuits, and whether they are operated mechanically or electrically, all interlocking schemes usually enforce several or all of the following rules:
- No signal can be pulled off unless corresponding points are set correctly.
- Facing points are locked to the corresponding route when a signal is pulled off.
- Signals for conflicting movements cannot be pulled off simultaneously.
- Points for conflicting routes cannot be set simultaneously.
- Trailing points are locked to the rear when a signal is pulled off.
- Distants, warners, repeaters, etc. cannot be pulled off unless the corresponding stop signals are pulled off.
- Gate stop signals cannot be pulled off unless level-crossing gates are blocked to road traffic.
The description of the possible routes that can be set, and the corresponding dispositions of points and signals are found in the locking table and selection table for a station. The locking table lists the signals and points controlled; the levers at signal boxes (or control panels at control centres) which operate various signals and points; which signals and points are locked (and in what position) when other signals are pulled off or points set; which track circuits are clear or occupied; etc.
The selection table lists the allowed non-conflicting routes that can be set. The terms route selection, route locking, route holding, and route release are used to describe the various steps in the process of picking a route for a train.
In various semi-automated systems of interlocking the electrical or electromechanical mechanisms or the electronic circuitry takes over a large part of the bookkeeping details that determine the sequences in which signals must be pulled off or points set to assign a route to a train. In the more primitive mechanical interlocking systems, such a sequence has to be manually followed; for this purpose the locking and selection tables are used by the signalman, along with lever leads which indicate for each signal lever which other levers must be set or cleared.
RRI and PI equipment is from Siemens and some British manufacturers. In recent years interlocking accomplished by modern integrated electronic circuitry instead of electromechanical relay systtems has come into use (Solid State Interlocking ('SSI'). [1/01] SSI is in place at 14 stations in India. SSI equipment is manufactured by RDSO. 210 stations have RRI installations, and 1970 have Panel Interlocking. [Update (3/2003)] 247 stations now have RRI installations and the number of stations with Panel Interlocking has risen to 2,426.
Q. What are the different levels or standards of interlocking that IR specifies for stations?
There are three levels of interlocking used by IR.
A Standard I interlocked station has mechanical interlocking. It also usually has just one running line and a loop line (and perhaps a couple of sidings). These are usually branch line stations. The points are worked by point levers situated near the points, and the signals are worked from interlocking frames in the signal cabin. The mechanisms use keys such that a key obtained from the points mechanism after setting the points must be used on the signal post locking mechanism to pull off the corresponding signal(s) and also to operate the block instrument. Through running speed for trains is restricted to 50km/h.
A Standard II interlocked station may be mechanically or electrically interlocked (usually the latter). These are usually non-trunk main line stations. The main running line at such a station can be completely isolated from the loops and shunting sidings on both sides. In electrically interlocked systems, setting the points activates electrical circuitry that enables or disables the appropriate signal levers and block instruments. Through running speed for trains is restricted to 75km/h.
Standard I and II stations sometimes do not have starter signals, only home signals for receiving trains; in such a case trains are dispatched using flag or lamp signals from the station. Standard I and II stations usually have only one signal cabin.
A Standard III interlocked station has points and signals that are either interconnected mechanically within the same mechanism, or electrically as with route-relay and panel interlocking. These are usually stations on trunk routes. Usually two signal cabins whose signal and points controls are interconnected are provided. These stations usually have the full complement of home and starter signals for receiving and dispatching trains. Through running speed for such stations is limited only by the speed limit for the section. The loop lines at such stations have to be completely isolated from the main running line by means such as sand humps, over-run lines, trap points, or derailing switches, etc.
Standard III.I (or III/I) is another designation found for some stations, which indicates that the station is rated as for Standard III, but the loop lines are not physically isolated on one side of the station. Similarly, a Standard II.I (or II/I) station is rated as in Standard II, but has loop lines or sidings that are not completely isolated on one side of the station.
Block Working classification of stations Stations are also classified as 'Class A', 'Class B', etc. See the classification of stations based on block working methods for more information on this.
Q. How are non-interlocked (NI) stations operated?
At stations with no interlocking between the points and the signals, the points have to be set appropriately and locked manually (either the key to operate them is removed, or the mechanism is externally padlocked) before pulling off a signal. The station master is personally responsible for ensuring that this is done and is supposed to carry the key to unlock the points with him. Trains are restricted to 15km/h over station limits. Non-interlocked stations are found only on sections with very light traffic.
Q. What are modified non-interlocked (MNI) stations?
Modified non-interlocked stations are those where setting and locking the points releases a key which has to be used to pull off a signal; however, the block instruments are operated independently. So there is some minimal amount of a safety lock between the points and the signals, but it does not qualify as full-fledged interlocking.
Q. What kinds of track circuits are used by IR?
The most common form of track circuit used is the detection of a train by the closing of an electrical circuit between the two rails because of the conducting nature of the rolling stock. This circuit may use DC in the simplest form, or may use AC.
Most zones now have many sections that use AFTC, or Audio-Frequency Track Circuit, that sends modulated electrical signals at a particular frequency (a few kHz, often 831.33Hz) through the rails rather than relying on a simple circuit connectivity; this is more reliable and allows the track circuit length to be increased a lot. The pioneers in adopting AFTC over simple DC track-circuiting were WR, SR, and CR (Dombivli, Pune-Lonavala, Chennai-Tambaram, Anand-Vatva, etc.). CR has also experimented with a variant known as the High-Frequency Track Circuit (HFTC).
Track circuits may also be 'coded', which means that the transmitted signal used in the track circuit is not a steady one (either DC or AC) but forms a pulse train of a particular pattern that can be used to distinguish different kinds of signals and allow overlay of different track-circuiting schemes if needed.
The Delhi Metro uses Coded Jointless AFTC which uses this method of coding the track-circuiting signal so that track circuits of different blocks do not interfere and do not need to be isolated electrically (more on this below). Jointless AFTC is also in use in a few other places on the IR network. It was first introduced on the Tambaram - Madras Beach section of SR. A variant called Pulsed High Voltage Track Circuit has also been used in a few places. AFTC equipment used by IR is from Adtranz, Siemens, US&S, and Alsthom. Jointless AFTC units are manufactured in India by Medha Ltd.
Track-circuiting is mandatory in sections where visibility is a problem, shunting operations are routinely carried out on the block section outside station limits on the main running line, or if special situations exist, e.g., if the advanced starter is more than one full train-length ahead of the most advanced trailing points of the station.
For a track circuit to reliably detect the location of a train within its specified section, the section must be electrically isolated from adjacent track (the exception being with jointless AFTC -- see below). For this, IR uses special kinds of rail joints, known as glued joints, especially on LWR (long welded rail) sections. Usually a special 940mm-long fishplate is used with 6 holes for fish bolts. Special high tensile strength fish bolts are used and the entire fishplate and bolt assembly is glued on to the joint, including the 'end post' at the joint, using an epoxy impregnated fabric in multiple layers. A typical glued joint is 6.5m long and is welded to the adjoining rails. The glue and fabric ensure that the rail sections on either side of the joint are electrically separated.
With jointless AFTC, electrical insulation is not necessary. Instead, detection of the section occupancy by a train is done by measuring the attenuation of the signal which is at a frequency (about 10kHz, usually) which does undergoes significant attenuation in rails over the distances of interest and whose propagation characteristics are known. This also means that the entrance of a train into the track circuit section is not determined precisely based on its position -- instead, safety factors are incorporated in the calculations to yield zones within which train occupancy can be determined in a guaranteed fashion. As mentioned above, the signal is also coded in a pulse train allowing the receiver to distinguish between signals of different track circuit sections.
In a variation of the jointless track-circuiting scheme, trackside units can be used to set up a resonant circuit and constrain the signal (usually between 1.5kHz and 3kHz) to a particular section of track. The advantage of jointless AFTC is clear in that insulated joints are not required, reducing maintenance, allowing the use of long welded rail sections, and eliminating the problems of insulated joint failures. Jointless AFTC sections can be 1-1.5km in length.
At normal joints within a track circuit section, electrical continuity must be ensured. Usually, one or two bonding wires are provided that connect the two rails across a fishplated joint. This is done even though the fishplate normally provides electrical continuity, to allow permanent way operations that involve unbolting the fishplates to continue without interfering with track circuiting. Also, dirt and surface impurities can cause the bolted fishplate joint not to conduct electricity reliably for track circuiting purposes (especially with AFTC or HFTC where the impedance of the joint to the particular frequencies involved is critical). In a few cases special-purpose resonant bonds or or other devices are provided at joints to allow particular track circuit signals (AFTC or HFTC) to flow while blocking others.
On most sections with track circuiting, track integrity checks are also provided with these circuits, which electrically detect a break in the circuit which would indicate a break or deformity in the rails. When interlocked with signals, this also prevents a signal from being pulled off if the track has a defect. Of course, not all kinds of track defects can be detected in this manner. IR mostly uses single-rail track circuiting for track integrity checking, although there are few sections with double-rail DC track circuits.
Q. What's the 'clearing point' or 'fouling point' or 'fouling mark'? What is 'overlap'?
The clearing point is the point ahead of a stop signal up to which the track must be kept clear of obstructions in order for a train to be accepted from the rear of the signal. In most cases this is with reference to home or outer home signals guarding entrance to station limits from a block section. The distance from the stop signal to the clearing point is the overlap (also overrun, or clearing distance).
The overlap is usually about 400m or so with lower-quadrant or 2-aspect signalling, and 180m with modified lower-quadrant, upper-quadrant, or MACL signalling where warners or distants protect the approach to the stop signal. No trains may be parked to the rear of the clearing point on the track protected by the stop signal. This provides a margin of safety in case a train overshoots a stop signal which is on, because of brake failure, driver inattention, etc.
The fouling point or fouling mark is a point to the rear of a converging junction, such that a train must be to the rear of that point in order to ensure that any train moving on the other converging line can proceed without being obstructed.
Stop signals guarding convergences are usually placed some distance to the rear of the fouling point for the junction; this distance is also known as the overlap, and again, provides a margin of safety against trains overshooting the stop signal. A similar safety distance is maintained ahead of the last stop signal of a station, before pulling off signals for a departing train; this is usually 120m or so.
Fouling points are usually marked by a stone or cement slab with 'FP' written on it by the side of the tracks.
The fouling point may also be marked for a siding to indicate that a rake must be stopped beyond it in order to avoid obstructing other trains passing by on the through tracks or on to other sidings. A number on it indicates the number of standard coaches or wagons that may be safely stabled on that siding.
Q. What are the last-vehicle indications that IR uses?
The last vehicle of a train is supposed to carry a red lamp at the rear. Earlier, the requirement was for merely an oil lamp, which was often missing or very feeble. In recent years provision of an electric lamp has become more common (it is mandated in the rules).
Last vehicle indications are of different types. A large 'X' is often seen painted on the rear of the coach that is the last one. A set of concentric circles may also be seen, although this seems to be going out of use now. EMU/DMU rakes have a smaller painted 'X' (red on white) at the rear, or sometimes a series of diagonal strokes painted on. (These painted symbols are all in addition to the lamp mentioned above.) In addition, a small board with 'LV' (black on yellow) is often attached to the rear of the vehicle (it stands for Last Vehicle).
If a train passes by a station or signal cabin without the appropriate last vehicle indication (or without confirmation of the number of coaches or wagons as mentioned above), it is assumed that the train has parted and suitable emergency procedures are brought into play.
There are some cases where a Last Vehicle indication is not required -- for instance, when the number of coaches or wagons in a train can be passed on to each block section after verification from the previous block section at the time the Line Clear indication is obtained (and with exchange of private numbers). The information is also provided to the section controllers. In some cases when working entirely within one block section, an 'LV' sign is not needed, if the number of coaches or wagons is communicated telephonically to the next station.
Q. Does IR have axle counters, hotspot detectors, trailing equipment detectors, etc.?
[5/99] Axle counters are widely used by IR to ensure that all wagons or coaches of a train have indeed passed a given point — out of a block section, out of the station limits, out of yard limits, other point zones, etc. ('last vehicle proving', 'block proving', or 'block verification', serving the same purpose as the visual 'Last Vehicle Check' or LVC that is done otherwise).
Axle counters are often used along with track circuits to control automatic block signals (i.e., to detect the presence of a train in a section. Axle counters may be of the single or multiple entry type. Axle counters today are mostly of the electronic variety. They use piezoelectric sensors on the tracks, which are triggered by the weight of a pair of wheels moving over them. Older models with mechanical sensors have also been used.
Usually two sensors are installed, at either end of the track section to be monitored, although more complex installations with more sensors are sometimes used. The counts of axles registered by each sensor are compared with logic taking into account the direction of motion, etc., to yield a final result of whether the section is clear or occupied. Signals and points are interlocked with the occupancy indication from the axle counter so as to prevent trains from being routed to occupied sections.
The counting and logic was electrical (relays) earlier, and is now handled by solid-state circuitry ('SSDAC' = solid-state digital axle counter, also generically termed an 'electronic axle counter') which apart from being more reliable and accurate is also more compact. A typical axle counter is usually able to handle track sections up to a few km in length, and train speeds of well over 200km/h; maximum counts registered by sensors may be quite high, as much as 16,000 (not for long trains (!), but to keep track of total traffic in a given period, etc.).
As with much other trackside equipment, the sensors are usually powered by a 24V DC supply; there may be battery back-ups for reliability. In the case of solid-state equipment, there are even redundant computation paths provided so that the final decision of track occupancy is done with a '2 out of 2' or 'best of 3' choice from multiple logic units.
Even with all this the axle counts are not 100% accurate and there are sometimes glitches in the counts. One sometimes sees small rooms marked 'Axle Counter Room' near the station master's office where the equipment for reading the axle counts is housed. One of the supplies of digital axle counters in India is Applied Electro-Magnetics India, Ltd. The use of axle counters was pioneered by WR and CR. Over 65,000 are now used across India [2003].
IR does not appear to have begun using any hotspot detectors or trailing equipment detectors or other methods for automatic detection of mechanical problems in rolling stock.
Q. Are there any in-cab signalling methods, ATP, etc. used by IR?
[5/99] Some WAP / WAM models have in-cab AWS / ATS (auxiliary warning system, automatic train stop). AWS provides prior in-cab notification of distant or home signals that are displaying danger or 'on'. ATS provides for a locomotive to be brought to a halt in case it overshoots an 'on' signal that it should not have.
This has been tried out on the Mughalsarai-Howrah section (ER) but is not in wide use although it was installed in the 1980s. (Pilferage of the track equipment is said to have been one reason for slow adoption by the railways.) Some Mumbai-area suburban EMU routes of WR and CR have ATS and AWS systems (WR had AWS from the 1980s, while CR got it more recently, in 2000).
If a signal at Caution is passed at above 25km/h, a buzzer sounds in the cabin and the motorman has to respond within 15 seconds to avoid application of the emergency brakes. The system also halts the EMU rake if a signal at danger is passed. The lineside transmitter for this is placed in between the rails a short distance before the signal, and the receiver for this is placed on the leading truck of the loco. CR EMUs do not have this system [7/00] and run without its benefit on WR tracks.
AWS systems usually work by means of electromagnets placed on the track that are activated by the signal aspects and whose magnetic fields are sensed by the AWS sensor mounted on the loco. A variation of AWS is being tried out [6/02] on the Delhi-Mathura section where instead of using magnetic sensors a radio signal is used to activate the buzzer or other alerting device for the driver.
[11/99] A system of loco identification and automatic proximity alerts has been proposed for the Konkan Railway. In this scheme, each loco would carry a beacon that transmitted its identification, including the train number, direction, etc. Ground-based receivers would pick up the beacon signals and relay the information to traffic control centres. Also, if there were other locos within a short distance (2km?) with the same beacon system, an alert would sound in the loco cab. This same system (or a similar one?) is also to be introduced on NFR [7/00].
Anti-collision devices (ACD) that will bring a train to a halt if it is within a certain distance to another train on the same tracks have also been proposed [7/01]. These were developed by Konkan Railway. These depend on computing the 'crossing number', a measure that takes into account the converging and diverging routes encountered by a train in order to figure out whether two trains that appear dangerously close (detected by means of radio beacons) are in fact safe because they are on different adjacent tracks, or not. ACD deployment began on Konkan Railway and now [12/04] there are plans to use them on nearly 3,500 route-km of NR, NFR, SR, SCR, and SWR.
Some WCAM-1 locos have a transceiver that is supposed to alert the driver of a derailment or other problem ahead. Very few locos seem to be equipped with this. [1/00] A version of ATP using Siemens ZUB equipment has been deployed in portions of the Calcutta and Bombay suburban systems. (How extensive is this?)
[4/00] IR is looking into procuring ETCS level 2 equipment to be installed on the trunk lines betweeen the four major metropolises, and later on other main lines. ETCS level 2 equipment allows for communication of target speeds, safe braking distances, etc. from lineside equipment to the on-board computers of the loco. It includes a measure of ATP (Automatic train protection) in that it can slow down or stop a train if required when the driver exceeds the safe speeds for given signal aspects; but it does not include full ATC (automatic train control).
[4/00] A pilot ETCS installation for an 84km stretch of the Delhi-Mathura line is planned with 40 locomotives to be fitted with the equipment.
[2/01] A system of ATC is being tried out for the Calcutta Metro. When deployed (expected some time in 2001) this will allow for automated routine operations, and reduced headway of 8 or even 5 minutes between the trains (currently headway is 10 minutes on the metro).
[6/03] The Delhi Metro uses in-cab signalling and is planning the use of ATC / ATO operation of the subway trains.
Mobile Trunk Radio Communications (MTRC) is used on some sections (Bhusawal - Itarsi, Itarsi - Nagpur, Nagpur - Durg). This is an older analog system dating to the 1980s, which allows the Traction Loco Controller to talk by radio to train crew that are carrying a receiver with them in the locomotive cab. Digital versions of MTRC have been considered and are slated for trials soon [2/05].
[12/04] IR is also considering the use of GSM-R technology on parts of its network. Siemens AG is supplying GSM-R equipment for 700 route-km of the NFR in West Bengal, Assam, and Bihar as an initial project for IR to experiment with the technology. [5/05] The North Central and East Central zones are also setting up some GSM-R services. GSM-R is a set of standards for railway-specific communications, integrating voice, data, and control communications, which is based on the popular GSM standard for mobile telephone communications.
[5/05] A Train Protection and Warning System (TPWS), based on ETCS Level 1 has been proposed for the Chennai Beach - Gummidipoondi section. EMUs will be monitored using track balises and lineside transmission devices (LEU or Lineside Electronic Unit). Signal aspects will be available in the EMU cab, and EMUs will be automatically braked if its speed is in excess of the safe speed appropriate for the signal aspect.
Anti-collision Device (ACD) Konkan Railway has developed a system involving radio receivers and transmitters fitted on locomotives, which aims to prevent or minimize the chances of collisions. The transmitter sends out a coded signal that identifies the train and its direction, route, etc.
Proximity and directional sensors and circuitry to handle the train identification information from other transmitters in the vicinity allows the ACD to sound an alarm and/or apply the brakes if it discovers that two trains have been routed on to the same track. Some versions of the ACD are also said to include the use of GPS to provide accurate information on the location of each train.
The ACD equipment has been put to use in several sections. It has been claimd [6/03] that equipment-related accidents have gone down substantially in the Jalandhar-Amritsar section because of ACDs.
Some zones of IR have recently [12/04] been experimenting with using GPS to report train positions and expected arrival times, etc.
Q. What other methods of communication with train crew are used on IR?
Handheld radios (walkie talkie sets) are widely used now (since the late 1990s) by train crew, yard crew, etc.). Some stations have transmitters allowing them to broadcast to all walkie talkies in the vicinity. Often, because of their higher power they are able to transmit to walkie talkie sets carried by crew that are farther away than the distance the walkie talkies can normally operate within, so that they cannot receive any messages in the reverse direction in such cases!
The Rajdhani Expresses still use a primitive though reliable form of communication. A pair of wires are connected to a telephone socket on the end of the first Rajdhani coach, usually a generator van. This telephone line then goes through the entire rake to the last coach where the guard has a telephone instrument. The driver also has a portable instrument which he plugs into this wire and communication between the guard and driver becomes possible even if the walkie talkies cannot function for some reason.
Q. What systems does IR use for control and reporting of signals and related equipment?
Panel Interlocking or Route Relay Interlocking are common in most busy stations. Usually, with these the aspects of all signals and positions of trains in various track sections is shown on a control panel. The control circuits usually use underground cables along the track, and sometimes overhead cables. Trackside cables are not used much because of the possibility of pilferage and sabotage.
Many areas have data logging equipment for each piece of signal equipment, which records information on the functioning of the signal and sends it to a computer at a central point (usually the division headquarters) where reports can be generated and alarms raised for various kinds of malfunctions (power failure, signal passed at danger, train entering without line clear, signal lamp failure, loose packing of points, etc.). A typical data logger used in such a system monitors all signal equipment and track circuits 5-50 times a second and signal power supplies every second.
History of interlocking in India
Historically, before the advent of block instruments, access to sections of railway tracks was done by the issuance of 'Line Clear' certificates (analogous to the use of track warrants in the USA) by the station-masters of the stations to which the sections belonged. The GIPR and EIR were in the forefront of mechanizing this process by installing block instruments, semaphore signals, and interlocking. Paper Line Clear tickets are still used in special circumstances and when communications have been disrupted.
Early days
The List system of interlocking (named for G H List) for signalling was introduced in 1892 at six single-line crossing stations of the North Western Railway. These employed a detector and locking system for protecting facing points. The system was enhanced by A Morse and came to be known as List & Morse interlocking.
The earliest full cabin interlocking arrangements were installed by the GIPR on its Bombay-Delhi route in 1893 with equipment from Saxby and Farmer of the UK. (Equipment devised by John Saxby.) Ajmer station was another of the early ones to get interlocking, as were the stations on the Lonavala-Pune route. The List & Morse system (devised by G H List and A Morse) was employed at 29 (or 28?) single-line crossing stations between Lahore and Ghaziabad in 1894.
Other improvements included the Hepper's Electric Key Transmitter. Invented by Major Lawless Hepper, a signal engineer of the North Western Railway this system replaced manual key interlocking. (Major Hepper (later Sir Lawless) later became the General Manager of the GIPR. His earlier invention, the Hepper's Key Instrument, which dispensed keys for the manual operation of points too far from the cabin for lever frames, was used extensively as well.)
Improvements and new systems
The adoption of cabin interlocking progressed rapidly and by 1912 almost the entire Bombay-Delhi route was equipped with it by the GIPR. Syke's Lock and Block systems were introduced on the BB&CI Rly. and others starting in 1910 or so. Around this time track circuits and power signalling (electric and electro-pneumatic) were also introduced for points and signals
These were used at major stations such as Bombay, Madras, and Calcutta. By 1931 more than 700 stations across India had interlocking. Lever frames from Tyer & Co., Westinghouse (60- or 70-lever frames were not uncommon) and others, and all-electric frames from Siemens (e.g., at Madras Egmore and Madras Beach in 1935) were in use, as were many locally built lever frames based on various British designs.
Various forms of single-line signalling were developed early, influenced by British designs but heavily modified locally. Double-wire signalling, devised by E W Baker of the Assam Bengal Railway came into use for operation of points and signals and was also used on the South Indian Railway. This allowed the use of steel wires instead of rodding arrangements. The South Indian Railway and the Assam Bengal Railway were the first to adopt this.
In other places, double-line signalling instruments were similar to those of the London and North Western Railway, as the same engineer had worked at the LNWR. (His name is not known -- clues?) Individual hand levers for points were heavily used, operated by various systems of key interlocking.
Power signalling started to be used much more in the 1930s. Many of these arrangements were of an American style, and operated 3-position upper quadrant signals – an American feature – even though general practice at the time was to use two-position lower quadrant signals.
The use of electropneumatic and electromechanical systems spread widely in the 1930s. Around 1945 Bandra station boasted an all-electric interlocking frame.
Proceed to the section on block and non-block system of train working.
