Rail SignallingA.K. ShrivastavSr Professor (S&T)Railway SignallingOrganisationAbbreviationType of SignalORGANIZATION OF S&T DPART!NTRAI"#A$ %OARD&'AIR!AN!!%R "&TRI&A"!!%R TRAFFI&!!%R TRAFFI&!!%R !&'ANI&A"!!%R !&'ANI&A"!!%R NGINRING!!%R NGINRING!!%R STAFF!!%R STAFFF&F&ADDITIONA" !!%R(SIGNA")ADDITIONA" !!%R(T"&O!)(&)TI* DIR&TOR(SIGNA")(&)TI* DIR&TOR(T"&O!)DIR&TOR (SIGNA")DIR&TOR (T"&O!)ORGANIZATION OF S&T DPART!NTZONA" RAI"#A$SG!&'IF S&T NGG.(&ST)&'IF S&T NGG.(&ST)&&&O!&O! &AO+&&ST+& &+& FA&&AO+&D$.&ST+&SR.DST+&DST+&N,AST+&D$.&ST+&+'-SST+&+'-ORGANIZATION OF S&T DPART!NTDI*ISION DR!Sr.DO!Sr.DO!Sr.DST + DSTSr.D!Sr.D!DS&DS&ASTADR!S)PR*ISORS)PR*ISORS&TIONA"NGG.Sr.S&TIONA"NGG.OFFI& S)PDT.&'IF D.!ANT"P'ONS)PDT./)NIORNGG.ORGANIZATION OF S&T DPART!NTAbbreviationLQ Lower QuadrantMAUQ Multiple Aspect Upper QuadrantMACLS Multiple Aspect Color Light Signal! anel !nterloc"ingRR! Route Relay !nterloc"ingSS! Solid State !nterloc"ing#SS #irst Stop SignalAbbreviationLSS Last Stop SignalA$S Absolute $loc" Syste%!$& !nter%idiate $loc" &ut$AC $loc" roving $y A'le counterCTC Centralised Traffic ControlTC Trac" CircuitA#TC Audio #re(uency Trac" CircuitDevelo01ent of Signalling on In2ian Rail3a4s Re56ire1ents of Rail Signallingvol6tionof Signalling S4ste1s%asi7 &on7e0ts ofSignallingI10ortant Definitions The physical appearance of a signal as seen by a driver is called the aspect of a signal. Aspect may be a position of the arm (0 degree, 45 or 90 degrees) of a semaphore signal during day time or colour of the roundel (red, yellow or green during night time) or colour of a lens in case of colour light signals both during day and night.Aspect of a SignalThe information the aspect of signal conveys is called the indication. Two types of signals called stop signals and permissive signals are used on Indian Railways. Stop signals can have a maximum of 4 Aspects and Permissive signals 3 Aspects. Indication Type of Signals#i'ed Signal&and Signal)etonator Signal#lare SignalSignalMechanicalLower QuadrantUpper QuadrantColor LightSe1a0hore SignalsMAUQLQ#i'ed SignalRunning SignalStop Signal er%issive SignalSubsidiary SignalStop SignalOuter&o%eStarterAdvance StarterINDICATIONASPECT STOP SIGNAL PERMISSIVE SIGNALSTOPSTOP DEAD NOT APPLICABLECAUTIONBE PREPARED TO STOPATNEXT SIGNALBE PREPARED TO STOPATNEXT SIGNALATTENTIONBEPREPAREDTO PASS NEXT SIGNAL ATRESTRICTED SPEEDBEPREPAREDTO PASS NEXT SIGNAL ATRESTRICTED SPEEDPROCEEDPROCEED PROCEEDPermissive Signals do not have Stop Aspect&olo6r light Sto0 signal in !6lti0le Three8As0e7t Signalling Territor4 9On9 0osition 9Off9 0osition

Se1a0hore Sto0 Signal in T3o8As0e7t Signalling Territor4 9On90osition 9Off9 0osition Se1a0hore Sto0 signal in the !6lti0le8As0e7t Signalling Territor49On9 0osition 9Off9 0osition

er%issive Signal)istant*arnerSe%aphore #arner signal in Two+Aspect Signalling Territory,below a stop signal 'On' position -Off- position #arner OFFSe%aphore *arner signal in two,aspectSignalling Territory,on a post by itself 'On' position 'Of' position !iniat6re Se1a0hore Ar1 t40e Sh6nt signal in T3o8As0e7t Signalling Territor4-On- position-Off- positon

Se%aphore Distant signal in Multiple,aspect Signalling Territory -On- position -Off- position

:.; !Subsidary SignalCalling OnShuntRepeaterStarter !ndicatorSubsidiary Signal1. Calling on Signals2. Shunt Signals3. Repeating Signals4. Starter Indicator Calling on Signals1.Placed below a Stop Signal governing the approach of a train.2. Not wored at the sa!e ti!e as the Stop Sig.3. "aen #$$ onl% after the train has been brought to a stop. &'chieved b% "rac( circuit and "i!e(dela% circuit). !iniat6re Se1a0hore Ar1 t40e &alling8on signal in T3o8As0e7t Signalling Territor4 9On9 0osition 9Off9 0osition

!iniat6re Se1a0hore Ar1 t40e &alling8on signal in !6lti0le8As0e7t Signalling Territor49On9 0osition Off9 0osition

&olo6r light t40e &alling8on signal in T3o8As0e7t Signalling Territor49On9 0osition9Off9 0osition &olo6r light t40e &alling8on signal in !6lti0le8As0e7t Signalling Territor4 9On9 0osition 9Off9 0osition Shunt Signal *sedforshuntingpurposesandnotapplicabletoarunning train. +a%beseparatel%locatedonpostsorclosetothegroundor below a stop signal. Shunt Sig. , +a% be of 1. +iniature 'R+2. -ISC 3. "he position light t%pe -On- position -Off- position

Dis7 t40e Sh6nt signal in T3o8As0e7t Signalling Territor4ASP&T< Sto0 Pro7ee2 slo3 Dis7 t40e Sh6nt signal in !6lti0le8As0e7t Signalling Territor4 -On- position -Off- positon

ASP&T< Sto0 Pro7ee2 slo3 !iniat6re Se1a0hore Ar1 t40e Sh6nt signal in !6lti0le8As0e7t Signalling Territor4 -On- position-Off- positon

RepeatingSignal,('Signalplacedinrearofafi.ed signalforthepurposeofrepeatingtothedriverofan approaching train the aspects of fi.ed signal in advance is called a Repeating signal Repeating Signal . +a% be of1. /anner t%pe2. 'n ar! t%pe3. ' Colour loght signal Se1a0hore Ar1 t40e Re0eating signal in

%anner t40e Re0eating signal in T3o8As0e7t Signalling Territor4 -On- position-Off- position ASP&T station at the other en2 of the =lo7> se7tionBlock Section 8 ortion of running line between two stations where no running train can enter until line clear is obtained fro% ne't station9Station Section Station SectionSTN A STN %$loc" Sectionstation limits 1eans the 0ortion of a rail3a4 3hi7h is 6n2er the 7ontrol of a Station !aster an2 is sit6ate2 =et3een the o6ter1ost signals of the station or as 1a4 =e s0e7ifie2 =4 s0e7ial instr67tions er%ission obtained fro% the station ahead for despatching a train in the $loc" sectionL!E "LEARauthorit# to proceed 1eans the a6thorit4 given to the Driver of a train 6n2er the s4ste1 of 3or>ing, to enter the =lo7> se7tion 3ith his trainThe line clear which is the permission to enter a block section is obtained by operating staf. Authority to proceed is the means adopted to convey this information to a driver. This may be (i) in the form of tangible authority viz. token, which is tied in a pouch and handed over to the driver, (ii) clearing of a signal, called Last Stop Signal(iii) issue of paper line clear, when there is a failure or the movement is not a normal movement (in case of runninga train in the wrong line due to an accident on the normal line)( Station Master)Authority to Proceedadequate distance 1eans the 2istan7e s6ffi7ient to ens6re safet4 Running Train The running train is a train which has started under an authority to proceed and has not completed its journey.Overla0&Signal Overlap$loc" Overlap"-< "o3er -6a2rant!A)- < !6lti0le As0e7t )00er -6a2rant!A&"S< !6lti0le As0e7t &olo6r "ight Signalling&olo6r "ight SignalsThe details of two types of overlaps are given belowName of overlapMeantfor signalPoint of considerationOverlap distanceBlock Last stop signal of the station in rearFrom frst stop signal LQ - 400 mMAUQ/MACLS- 180 mSignalNormallyfor Homesignals (manual sections)From starters (double lines) Fromoutermost trailing point (single line)LQ - 180 mMAUQ/MACLS - 120 mAllsignals (Automatic sections)From next signal in advance120 mRunning Line :- The defnition of running line is important as most of the main signals are meant for the running lines. Running lines are defned in G.R. as the lines with points or connections and governed by signals, used by a train when (i)entering a station (ii) leaving a station (iii) running through a station (iv) running between stations. If the line is used in any other condition, then that line is not a running line.The width of rolling stock is fxed on Indian Railways and the overall fxed dimensions of which is given in the schedule of dimensions. When two tracks are running parallel the distance between them should be such that two trains running in these tracks simultaneously do not infringe with each other. Hence a distance of (15 6) in case ofB.G. between the adjacent tracks are maintained. When two tracks join each other or cross each other, this distance between the two tracks starts reducing. The point at which the distance starts reducingfrom a standard distance of(15 -6) is very important from safety point of view. A permanent mark (FM or FP) is provided at the track level. This mark is called fouling mark .Fouling Mark (FM)It is the responsibility of the driver to ensure that the engine is clear of thefouling mark and the guard to ensure that the fouling mark is cleared by the last vehicleCollisionCollisionO!.T 8 oint is a %echanis% provided in the trac" to facilitate diversion : 0ngines donot have steering wheel as available in %otor cars;Facing and Trailing Points :- Points are used to divert a train from one line to another. Points are classifed as facing or trailing depending on the direction of movement of trains over the point. If the direction of movement is such that the trains get diverted while going over the points, these points are classifed as facing points. Ontheotherhand,iftrain approaches a point with two lines converging to one, that point is called a trailing point. Fa7ing Point Trailing Pointoint9A t9$ and under the Absolute $loc" Syste% consist of three classes, &lass 9A9 stations , where Line Clear %ay not be given for a train unless the line on which it is intended to receive the train is clear for at least ?33 %eters beyond the &o%e signal1 or upto the Starter> &lass 9%9 stations , where Line Clear %ay be given for a train before the line has been cleared for the reception of the train within the station section> and &lass 9&9 stations , bloc" huts1 at which no trains are boo"ed to stop9 This shall include an !nter%ediate $loc" ost9 :@; Non8=lo7> stations or &lass 9D9 stations are stopping places which are situated between two consecutive bloc" stations1 and do not for% the boundary of any bloc" section9 &lassifi7ation ofStations Station %lo7> StationNon %lo7> Station)river %ust obtain an authority to proceed enter the bloc" section with his train&lass A &lass %&lass &&lass DStopping laces between two consecutive bloc" stations : do not form boundary of any block station; Any station which cannot be wor"ed under A1 $1C or ) class conditions8 S0e7ial &lass 8 :MUST &AA0 T&0 AROAAL O# &RS8 &o11issioner Rail3a4 Safet4;&lass 9A9 stations 8 3here "ine &lear 1a4 not =e given for a train 6nless the line on 3hi7h it is inten2e2 to re7eive the train is 7lear for at least ?@@ 1eters =e4on2 the 'o1e signal, or 60to the StarterA &lass 9A9 stations 8 3here "ine &lear 1a4 not =e given for a train 6nless the line on 3hi7h it is inten2e2 to re7eive the train is 7lear for at least ?@@ 1eters =e4on2 the 'o1e signal, or 60to the StarterA &lass 9%9 stations , where Line Clear %ay be given for a train before the line has been cleared for the reception of the train within the station section&lass 9%9 stations , where Line Clear %ay be given for a train before the line has been cleared for the reception of the train within the station section&lass 9&9 stations , bloc" huts1where Line Clear %ay not be given unless the whole of the last preceding train has passed atleast ?33 M beyond the &o%e signal and is continuing its Bourney9 &lass 9&9 stations , bloc" huts1where Line Clear %ay not be given unless the whole of the last preceding train has passed atleast ?33 M beyond the &o%e signal and is continuing its Bourney9 Non8=lo7> stations or &lass 9D9 stations are stopping places which are situated between two consecutive bloc" stations1 and do not for% the boundary of any bloc" section9 C&lass %Train %eing Re7eive2 on "ine No. :":"B"CTrain %eing Re7eive2 on "ine No. :":"B"C!A&"S2D3 E 243!A&"S2D3 E 243DN Train %eing Re7eive2 on !ain "ine !A&"S2D3 E 243DN Train %eing Re7eive2 on !ain "ine !A&"S2D3 E 243DN Train %eing Re7eive2 on "ine C":"B"C!A&"S2D3 E 243DN Train %eing Re7eive2 on "ine C":"B"C!A&"S2D3 E 243DN Train %eing Re7eive2 on "ine C":"B"C!A&"S"IN : "IN ?"IN B"IN CIn2i7ate Signal As0e7ts for DN Train =eing re7eive2 on "ine ? along 3ith Signals, %oar2s, Overla0s. Rudimentary Interlocking :- The signalling system provided initially at a station, where two trains from the opposite directions can cross, consisted of an elementary type of interlocking between points and signals. The maximum speed was restricted to 15 kmph. Only one signal was provided at each side Since the location of the signal happened to be the place where policemen used to have their homes, this signal was named as Home signal. The signal has two aspects viz., on when the arm is horizontal, proceed when the arm is lowered to 45 to 60 degrees below the horizontal.A22e2DNo Signals for 2is0at7h of a Train A22e2A22e2 Isolation !A)-< !6lti0le As0e7t)00er -6a2rant Signalling (STD III)Factors afecting Braking Distance :- Important factors afecting braking distances are -1.Train Speed2.Train Load3.Gradient4.Brake Power5.Types of Brakes6.Condition of Rails7.Rail/Wheel AdhesionSighting Committee :- Fixed signals can be commissioned only after ascertaining the minimum visibility available for these signals. The visibility test is done by a Committee called Sighting Committee consisting of senior supervisors from motive power department (Electrical or Mechanical), trafc department and signal department. They will go by Footplate, or trolley and check the visibility during day and night. The signals can be commissioned only on clearance by Sighting Committee. Eforts are taken to improve visibility of semaphore arm, by providing tall posts so that the signal could be seen from a long distance. Similarly, in case of colour light signals,the visibility is improved by superior lens system :- In any station or yard there could be number of simultaneous movements. These movements should not interfere with each other. Besides, when loose vehicles (vehicles not attached to an engine)could roll and obstruct important lines, isolation is a method adopted to protect important lines in a station/yard. The important lines are those (i)where speed is above 50 kmph, (ii) all passenger lines as compared to goods lines/siding and (iii) goods lines as compared to sidings.Isolation There are three rules of isolation as given in Rules for Opening Railways. These rules ensure the protection of important lines. The rules are -(i)The line on which speed is higher than 50 kmph should be isolated from all other running lines.(ii)All passenger lines irrespective of the speed should be isolated from goods lines/sidings.(iii)It is desirable to isolate goods lines from sidings.Rules of IsolationRules (i) and (ii) are obligatory. Rule (iii) is optional.Methods of Isolation :- In all the methods of isolation, the two lines are not directly connected but through a cross over. The diferent methods are -(i)Trap Points :- Trap points are points with single switch. In the normal position or open position, when any vehicle passes over the point, it gets derailed. So, it is not desirable to provide trap points on lines where there are frequent movements.Dead End :- This is another method where instead of a trap point, the unimportant line is connected to a dead end, so that when any vehicles escape from this line or when there is simultaneous movements, the line will be set to dead end. The only disadvantage is that dead ends serve only as a method of isolation and no vehicle is permitted to be stabled on this line. Since the dead ends are connected to running lines, it is necessary to isolate them from sidings. IF any vehicle is stabled on a line it becomes a siding. In case, a stabling facility is required, dead end with trap point is provided.Dead End with Trap Points :- This method is adopted wherever a stabling facility is required.The brakes can be applied suddenly or gradually. When the brakes are applied suddenly, the braking distance required would be less but the rate of deceleration may cause discomfort to passengers and in case of freight trains, may damage the consignments. The braking distance with sudden application of brakes is called Emergency Braking Distance (EBD). The drivers are not supposed to apply sudden brake application unless there is emergency. The drivers are normally supposed to apply brakes gradually, so that the braking may not cause discomfort to passengers. The braking distance obtained with gradual application of brakes is called Service Braking Distance (SBD) or Normal Braking Distance (NBD). SBD is 1.2 times EBD. The intersignal distance is always based on Emergency Braking Distance.Types of Braking Distances : -Since the EBD for a Mail/Express train at 100 kmph is 1 km, inter-signal distance has been kept as 1 km. The diference between SBD and EBD is provided as an additional visibility distance for every signal.Reaction Time : - When the driver approaches and observes a signal, he can not be expected to instantaneously react to the aspect of a signal, but only after some time. This time is called the reaction time. When the driver is in the process of reacting to the aspect of a signal, the train is running at maximum speed and distance covered during this reaction time is called reaction distance (RD). The reaction distance on Indian Railway is taken as 200 m. Reaction Distance plays a crucial role while determining the minimum visibility required for a signal. Lower Quadrant System (2 Aspect) OUTER Sectional speed 100 KMPH or more :1200 MSectional Speed less than 100 KMPH 800M(Where above visibility cannot be achieved, Warner may be separated. With Warner separated, minimum visibility of OUTER cannot be less than 400 M)WARNER (on a post by itself) : 400 MHOME400 MMain StarterSignals400 MAll Other Signals200M !ini161 *isi=ilit4 Distan7e forSignalsFor Multiple Aspect SignalsDISTANT SIGNAL:400 M (An inner distant signal where provided shall be visible from a minimum distance of 200 M) ALL STOP SIGNALS : 200 MThe maximum speed of a train over facing point on the main line of a station depends on the equipments used at the points, signals provided, type of interlocking and provision of isolation between main line and other lines. There are four standards of interlocking used on Indian Railways permitting 15 kmph to maximum permissible speed. The set of equipments to be provided for diferent standards of interlocking is stipulated in the Signal Engineering Manual.In case of Std. I and Std. II, interlocking points are locally operated and locked by key locks. The key released from the key lock is inserted in the lock on the signal post before a signal can be cleared. Once the signal is cleared the key locking the points can not be taken out. Hence there is indirect interlocking between points and signals. The diference between Std. I and Std. II interlocking is the requirement of isolation, i.e. main line from other lines, as the maximum speed permitted is 75 kmph in Std. II.The main diference between Std. II and Std. III interlocking is the types of interlocking. Since in Std. II, points are operated locally and signals from a cabin, there is indirect interlocking between points and signals. Whereas in case of std. III, points and signals are operated from the same location and hence there is direct interlocking between points and signals. Standard II interlocking is not generally adopted in view of the necessity to send the staf for operating the points locally. In case of major and terminal stations, full compliments of Standard III interlocking are provided. In spite of that these stations are classifed as std. I because no isolation between passengers lines is provided at these stations. Do6=le Distant Signal)istant Signal!nner )istant Signal77/777/R777/&o%e Do6=le Distant Signal)istant Signal!nner )istant Signal77///777///R7 with Route777/&o%e Distant Signal< $$ < Sto00ing on !ain "ineA Or %eing Re72 on "oo0 "ineDistant Signal< G< %eing Re7eive2 on !ain "ine Do6=le Distant Signal)istant Signal!nner )istant Signal77///777///R7 with Route777/&o%e Distant Signal< $$ < Sto00ing on !ain "ineA Or %eing Re72 on "oo0 "ineDistant Signal< G< %eing Re7eive2 on !ain "ine Do6=le Distant Signal)istant Signal!nner )istant Signal77///777///R7 with Route777/&o%e Distant Signal< $$ < Sto00ing on !ain "ineA Or %eing Re72 on "oo0 "ineDistant Signal< G< %eing Re7eive2 on !ain "ine Signalling Layouts4 A LQ Single Line1 $ Class 2FM2D3M2?33 M2333 M?33 M?33 M4 A LQ Single Line1 $ Class 2?33 M2333 M2FM2D3M?33 M?33 M4 A LQ Single Line1 $ Class Aspect Control Chart#O !'SAS Sto0 at 'o1e 2?33 M2333 M2FM2D3M?33 M?33 M4 A LQ Single Line1 $ Class Aspect Control Chart#O !' !SAS Sto0 at !ain "ine Starter 2?33 M2333 M2FM2D3M?33 M?33 M4 A LQ Single Line1 $ Class Aspect Control Chart#O "' "SAS Sto0 at "oo0 line Starter 2?33 M2333 M2FM2D3M?33 M?33 M4 A LQ Single Line1 $ Class Aspect Control Chart#O !' !SAS R)N T'R) *ia !ain "ine 2?33 M2333 M2FM2D3M?33 M?33 M4 A LQ Single Line1 $ Class Aspect Control Chart#O "' "SAS R)N T'R) *ia "oo0 "ine !A&"S on Do6=le "ine2D3M2?33M243M2D3M!A&"S on Do6=le "ineU ). Co%%on Loop)P "oo0DN !ain)P !ainAuto%atic Signallingssentials of the A6to1ati7 %lo7> S4ste1 on 2o6=le line. ,:2; *here trains on a double line are wor"ed on the Auto%atic $loc" Syste%1 , :a; the line shall be provided with 7ontin6o6s tra7> 7ir76iting or aEle 7o6nters:b; the line between two adBacent bloc" stations %ay1 when re(uired1 be divided into a series of auto%atic bloc" signalling sections each of which is the portion of the running line between two consecutive Stop signals1 and the entry into each of which is governed by a Stop signal1 and :c; the trac" circuits or a'le counters shall so control the Stop signal governing the entry into an auto%atic bloc" signalling section that ,:i; the signal shall not ass61e an 9off9 as0e7t 6nless the line is 7lear not onl4 60to the neEt Sto0 signal in a2van7e =6t also for an a2e56ate 2istan7e =e4on2 it, and :ii ; the signal is a6to1ati7all4 0la7e2 to 9on9 as soon as it is 0asse2 =4 the train.:4; Unless otherwise directed by approved special instructions1 the ade(uate distance referred to in sub,caluse :i; of clause :c; of sub,rule :!; shall not be less than 243 %etres9ssentials of the A6to1ati7 %lo7> S4ste1 on single line.,:2; *here trains on a single line are wor"ed on the Auto%atic $loc" Syste%9, :a; the line shall be provided with continuous trac" circuiting or a'le counters1 :b; the 2ire7tion of the traffi7 shall =e esta=lishe2 onl4 after "ine &lear has =een o=taine2 fro1 the =lo7> station in a2van7e. :c; a train shall be started fro% one bloc" station to another only after the direction of traffic has been established9:d; it shall not be possible to obtain Line Clear unless the line is clear1 at the bloc" station fro% which Line Clear is obtained1 not only upto the first Stop signal but also for an ade(uate distance beyond it9Unless otherwise directed by approved special instructions1 the ade(uate distance referred to in clauses :d; of sub,rule :2; shall not be less than 2D3 %etres9D6ties of Driver an2 G6ar2 3hen an A6to1ati7 Sto0 signal on single line is to =e 0asse2 at 9on9. , :2; *hen a )river finds an Auto%atic Stop signal with an -A- %ar"er at -on-1 he shall bring his train to a stop in rear of that signal and wait there for one %inute by day and two %inutes by night9*hen an Auto%atic Stop signal has been passed at -on-1 the )river shall proceed with great caution until the ne't Stop signal is reached9 0ven if this signal is -off-1 the )river shall continue to loo" out for any possible obstuction short of the sa%e9 &e shall proceed cautiously upto that signal and shall act upon its indication only after he has reached it9 Types of Signals in Automatic Block Section :- Three types of signals are used in automatic block section :-(i) Automatic Signal(ii) Manual Signal(iii) Semi Automatic SignalIn a section provided with automatic block working, automatic signals are used in sections where there are no points or level crossing gates.Manual signals are used at the approach to stations, since in case of stations, signals are manually operated.Semi-automatic signals are those which can work either automatically or manually. Semiautomatic signals are provided in sections with a point or a level crossing gate or both. The semiautomatic signals are ftted with an illuminated (A) Marker. When the A marker is lit up, the signal works as an automatic signal. When the A marker is extinguished, the signal works as a manual signal.Automatic signal with a Gate and a Point :-When there is a gate and a point in an automatic block sections, two illuminated markers A and AG are provided. The indications given by these marks are -(i)Point set for normal main lines and gates closedA marker is lit upSignal works as an automatic signal.(ii)Point set for normal main lines and gates openAG marker is lit upSignal works as a gate signal(iii)Point not set for normal main lines Gate openA marker and AG marker extinguishedSignal works as a manual signal(iv)Point not set for normal main lines gate closed.Headway - The main purpose of providing an automatic signal is to increase the train density. The train density can be increased if the trains can follow one another at close intervals. The train density is generally indicated by the term headway. Headway is defned as the distance between two trains running in the same direction always getting proceed aspect.Headway with the three aspect signals - The second train can get a proceed aspect after the frst train clears two block sections and an overlap of 120 m. Since the minimum visibility required is 200 m., the headway in an automatic block section with three aspect signal (as shown in the fgure given below) is 2EBD+ 200m + 120 m + TL = 2.320 km + TL.%D : >1Automatic Block Section with four aspect signals - In case of am automatic section with 4 aspect signals, an automatic signal displaysCaution Aspect (Y) - When one block section +overlap of 120 m is clear.Attention Aspect (YY) - When two block section +overlap of 120 m are clear.Proceed Aspect (G) - When three block sections +overlap of 120 m are clear.The inter-signal distance in case of 4 Aspect signals is emergency braking distance between a signal showing 'Attention Aspect' (YY) and a signal at 'On' as shown in the following fgures :-

%D F %DThe headway in case of 4 Aspect signals is EBD + EBD + 200 + 120 + TL= 1.820 m + TLWith the provision of 4 aspect signals, Headway is reduced by 500 m, i.e. 25% and hence the train density can be increased by 25% as compared to 3 Aspect signals. Therefore, in very busy suburban sections like Bombay, four aspect automatic signals are provided.%D F %D:@@@ G ;@@G B@@G:B@ G T"A6to1ati7 SignalA !ar>erNor1al As0e7t $G$RA)enotes fully auto%atic signalcRo6te In2i7atorAG Sign&alling HONISh6nt A SignNor1al As0e7t $G$RSe1i A6to1ati7 SignalDenotes se1i a6to1ati7 signalAAG Sign&alling HONISh6nt Signal 3or>ing in A6to !o2eA< Points are set & lo7>e2 A SignAAG Sign&alling HONISh6nt Signal 3or>ing in A6to !o2eA< Points are set & lo7>e2 A SignAG Sign&alling HONISh6nt Signal given for 2iversion A SignAAG Sign&alling HONISh6nt Signal 3or>ing in A6to !o2eA< Points are set & lo7>e2A SignAG AG Sign&alling HONISh6nt Signal 3or>ing in A6to !o2eAG< Gate is o0en or has faile2, Points are set & lo7>e2 A SigncAG Sign&alling HONISh6nt Signal Faile2, &alling ON Given A SignAG Sign&alling HONISh6nt Sh6nt Signal Given A SignAGAAGIN&ORR

&TA&IN&ORR

&TSIGNAL OPERATION Two Types of Signals: Semaphore and Colour light signals. Semaphore signals can be operated through either single wire or double wires. single wire : A single wire is run from the cabin to the signal. The signal is operated by pulling the wire from the lever which in turn raises the counter weight lever at the signal post. When the distance of signal is more than 300 m, a device called cabin wire adjuster is provided in the cabin. The cabin wire adjuster is operated before pulling the signal lever to remove the sag. Disadvantages of single wire operation are (i) More possibility of outside interference. The signal can be operated by pulling the wire from outside or pressing the signal arm.(ii) Range of operation is only 950 m.(iii) It can be used only for two aspect signalling.(iv) Signal return is gravity based. Damage to down rod more prominent due to return impact of signal arm.Double Wire :- In this system, for operating any function viz. signal, point etc., two wires are used. The two main advantages of double wire system are - (i) outside interference totally eliminated and (ii) automatic compensation of temperature efects.The outside interference is eliminated by pre-tensioning the pull and push wire of the double wire system to 150 1b. by means of 205 1b. weights in the cabin. Because of pre-tensioning, it will not be possible to pull the wire from outside. The temperature efects are compensated by a device called compensator. Double wire compensators are provided for every point/signal and are generally located in the ground foor of the cabin. Three main functions of the double wire compensators are -(i) Pre-tensioning the wires to 150 1b. with 205 1b. weights.(ii) To maintain the transmission in constant tension by self-adjusting the variations in length due to temperature changes.(iii) When a break or disconnection occurs, the falling compensator ensures that the signal resumes its most restrictive aspect. Advantages of double wire operation of signals are (i) Outside interference eliminated.(ii) Automatic compensation against temperature changes.(iii) Range of operation increased to 1400 m.(iv) Can be used for two aspect or MAUQ signalling.(v) Signal return due to the operation of lever. Hence it is smooth and impact on the signal arm considerably less.(vi) Since the range of operation for signals is more, it is possible to have one central cabin and operate all points and signals from this cabin.Electrical Operation :- The range of operation is 950 m in case of single wire and 1400 in case of double wire. If any signal is located beyond this range, it will not be possible to operate this semaphore signal by mechanical means. In such cases electrical operation using signal machine is adopted. Signal machine consists of a 12v. direct current motor and other mechanical parts. Arm & Light Repeater :- Normally, a signal is visible from the place of operation/station master's ofce. Hence it will be possible to check whether a signal is cleared or not. During night time, to check the position of signal a small back light is provided. When the signal is at ON, this back light will be visible. When the signal is cleared, the back light is obstructed by a screen called back light screen. Whenever back light is not visible, it may be due to signals in the OFF position or signal lamp is extinguished.There may be cases where a semaphore signal is not visible from the place of operation. Electrical repeater is provided in ASM's ofce to indicate the position of a signal arm and the condition of a signal lamp. The electrical repeater is called Arm & Light Repeater (AR & LR). Arm repeater shows three position viz., On, Of and Wrong by a pointer. ( LQ: +/-5 deg. From HZ: ON; 45-60 deg: OFF; MAUQ: 40-45 deg: Caution/Attention; 85-90 deg : Proceed)The light repeater has two positions IN and OUT. The light repeater works by the expansion of thermostat in the oil litlamps. If the lamp is out, the point will show light OUT. A bell rings to attract the attention, whenever pointer is showing light out. (During day time, there is no lamp, to stop the bell, two position switch is provided in the AR & LR. If the switch is kept in day position, the bell will not ring. During the night time, the switch must be kept in the night position to get the bell warning in case of a signal lamp going out.)Colour light signals are used in modern signalling systems. The main advantages of colour light signals over are semaphore signals arei) Day and night aspects are same.ii) Range is considerably more.iii) It can be used to display more than 3 aspects.iv) Ease of operation.v) No moving parts In colour light signals, an electrical lamp operated with 12v and a superior lens assembly are provided to get a visibility around 1 km. The lens assembly consists of an inside coloured lens (red, yellow or green) and an outside plain lens. The assembly is called double combination of lenses. The signal lamp is kept at the focal point of the inner lens. Cascading or cutting in arrangement is adopted to prevent a blank signal. In the cascading arrangement whenever, a signal lamp of an aspect fuses, the next restrictive aspect is automatically brought in. For example, if a signal lamp is displaying green and the green lamp fuses, an yellow aspect will be displayed automatically. Similarly, if a signal is displaying yellow and the yellow lamp fuses, a red aspect will come automatically. But if a signal is showing red and the red lamp fuses, the signal will be blank. To prevent this occurrence, all red lamps are provided with two flaments. One main flament and an auxiliary flament. All of aspect lamps are provided with single flaments. Red aspect lamps of the stop signals and yellow aspect lamps of the Distant signals are provided with double flaments.The power supply failure is taken care of by providing three sources of power for colour light signals. Double line sections with 25 kv electric traction, the three sources of power are -i) power tapped from Down Line - Normal sourceii) power tapped from Up Line - Standby sourceiii) local power (power from Electricity Board or diesel generator).Single line sections with 25 kv electric traction i) power tapped from Up/Down line - Normal sourceii) local power (EB)iii) diesel generatorSections without electric tractioni) local power - Normal tractionii) 2 - diesel generatorsower Supply Arrange%ents at Signalling !nstallationsSource8 4@3A AC Single hase?2F A AC Three hase#i'ed Stop Signals for approaching train do not beco%e blan" when %ain power supply source failsRailway 0lectrified areasAu'iliary Transfor%ers by tapping fro% 4F GAO&0Separate Transfor%ers for ). H U Lines*here only One Line1 rovide )/ Setrovide Auto Changeover anel in ASMs Officeower Supply Arrange%ents.on 0lectrified areas#or Colour Light Signals1 ower Supply to be drawn fro% Station #eederrovide 4 )/ Setsrovide AutoIManual changeover panel in ASMJs Officerovide Solar panels for Se%aphore signalsSe0arate Transfor1ers to =e 6se2 for fee2ing Signals & Tra7> Fee2 &hargers (for Tra7> &ir76its)(ISTING PO#R S)PP"$ ARRANG!NTS!ndoorRelays24I4?I63AOutdoor Relays24I4?I63A223 Aoints4? AA'leCounterUp Side$loc" Line)n Side$loc" Line)n Side$loc"Local230 V AC BUSAoltageRegulatorTransfor%ers Signal "ightingTransfor%ersTra7> fee2&hargersS! PanelIn2i7ation230 V AC BUSUp Side$loc"LocalKLKLKLKLKLKLKLKL)$$C)$$CTransfor%ersAC ower Source"onventional Stand b# Arrangement Diesel Generator SetS!PS=ase2IPS KLLK?3A:SMS;@33 A&$attery$an"2GAA)C , )CConverters:*ith standbys;223 A)C223 A )C $USTransfor%ers4@3I223ATrac" #eed ChargersSignals To different )C CircuitsStatusMonitoringin ASMJsroo%CAT12GAATransfor%ers4@3I223ACAT)C,)CConvertert9 Machine$lock diagram of S%PS based PS s#stem AutoChangeOverKK!nvertersKKTrac" C"ts9)C Loads Signals223A )CSwitch Mode RectifiersAC 2F3 A,453A F3 &M$atteryTransfor%ersntegrated Po&er Suppl# S#stem Advantages of !S"hereisnoneedtorun-0atPIStnin Non(R1areaiftheco!!ercialpoweris available for an average of 2(3 hours4da%.No blan signals.'vailabilit% 5 reliabilit% is ver% high +aintenance re6uire!ent is ver% low including that of batter% 5 -0 sets.Saving in Po3er , ower consu%ed by !S is sa%e as the power consu%edby e'isting conventional power supply syste%9!n the e'isting installations the )/ set is re(uired to run for an average of 6 hoursIday :Cost of diesel for running of )/ set is appro'i%ately Rs9 541F33I, per yearIstation9Advantages of !SSafety considerations to be fulflled in the operation of a point especially facing point. The considerations are -i) A suitable means to set the point to one of the two positions.ii) A lock to prevent the movement of the switches due to the vibration of train.iii) To prevent the operation of point when it is occupied by a vehicle.iv) Means to ensure that closed switch is housed and locked properly.oint Operation Setting - A point is said to be set :-i) when the gap between open switch and stock rail is less than 5 mm andii) when the gap between open switch and stock rail is 115 mm in case of BG. and 100 mm in case of MG.The points can be set either locally or from a central location The central operation can be through (I) Mechanical means and (ii) Electrical means Mechanical operation can be provided through (I) Rodding or (ii) Double wires.Where signals are operated by double wire, points can also be operated by double wire. The double wire operation has a range of about 700 m. The double wires are provided with a compensators for automatic compensation. In modern signalling systems, the points are electrically operated. The main advantages of electrical operations are :-i) Range unlimitedii) Ease of operationiii) More reliableiv) Less maintenanceLocking of a point - It is necessary to lock a point especially a facing point to prevent the movement of switches due to the vibration of a train. Diferent methods can be adopted for locking depending on the maximum speed permitted over the points.8.4.2 Padlock locks and clamps - In this arrangement, a clamp is provided between closed switch and stock rail and the clamp is locked with a padlock. This arrangement is suitable for speeds upto 15 kmph.8.4.3 Key Lock - Key lock is an arrangement provided between the tracks in a point assembly to lock the switches. The switches are locked by means of a plunger in the key lock unit. When the locking is proper, a key is taken out from the key lock. The key lock arrangement is adopted with locally operated points for speeds upto 50 kmph. The key released from a key lock unit has to be inserted in the signal post to lower a signal. When the signal is lowered, the key gets locked in the signal post and hence point can not be disturbed. Thus, there is indirect interlocking by means of a key between points and signals. Hand Plunger Locks - This is an improved system of key locking and can be used with locally operated point for speeds upto 75 kmph.8.4.5 Facing Point Locks (FPL) - This arrangement is adopted with mechanically operated points from a central cabin. The locking is actuated by a plunger in the Facing Point Lock unit at the point through point rodding from the cabin. The point rodding for FPL are also provided with rodding compensator for compensation against temperature efects.8.4.6 Point Machines - Point machines which are used to operate the points electrically have also the locking facility provided inside the machines.points are operated from central cabin by (1) Rodding (2) Double wire and (3) Point machine. Route Holding - It is very essential to ensure that the points are not unlocked when a vehicle is over the point. The arrangement provided for this purpose is called route holding. In case of key locked points, by virtue of location of a key lock unit in between the tracks, route holding feature is available. If the vehicle is over the points, the key lock is not accessible and hence, it will not be possible to insert the key and unlock a point.In case of facing point locks, a device called lock bar is provided for the purpose of route holding. Lock bar is a mild steel angle of size 50 mm x 50 mm and of length 13 m (42') in case of BG and 12.2 m (40') in case of MG. The lock bar is ftted closed to the tip of the switch and remains 38 mm (1 ") below the rail top. When a point is to be unlocked, the lock bar rises to the rail top and then goes below. If there is a wheel standing on the rail, i.e. point is occupied, the lock bar cannot rise and hence the point can not be unlocked. The length of the lock bar has to be more than the maximum distance between the longest wheel base of any rolling stock.In case of electrically operated points, route holding is achieved by a device called track circuits Mechanical Detectors - Two types of mechanical detectors are used. One is with single wire and the other is with double wire. The single wire transmission operating the signal is passed through a detector, provided at the facing point, called 'unit detector'. The unit detector ensures that signal transmission wire can move only if the facing points in the route are set correctly and locked. In case of a double wire operated point, a rotary type detector is used. This detector lever is required to be operated before the operation of the signal lever. If the points are not set properly, the detector lever cannot be operated and hence signals cannot be operated.Point machines have electrical contacts inside the machine to ensure that the points are correctly set and locked. Point machines perform three operation viz, setting, locking and detection.O=str67tion Test for PointsF %% obstruction at 2F3 %% fro% toeThe functioning of the detector is checked by test called an 'obstruction test'. In this test a physical obstruction is provided between the stock rail and closed switch and it is seen whether the detector fails with this obstruction. 'an2 Pl6nger "o7>"o7> %ar)NIT DT&TORPoint !a7hinesO=str67tion TestESSENTIALS OF INTERLOCKING Interlocking is a safety arrangement to ensure that points, signals and other connected equipments are operated in a predetermined sequence. Four Essentials of the Interlocking stipulated in the Signal Engineering Manual :29 Route SettingIt should not be possible to take of a signal unless the Route is properly set. Route setting involves (1) setting of all points viz. facing, trailing and isolation, (2) locking the facing points in case of rod operated points, locking all points in case of D.W. or electrically operated points, (3) closing and locking the interlocking level crossing gate against road trafc, not only for the line on which the train is going to run but also for the signal overlap. 2. Route HoldingIt should not be possible to change a point, unlock a facing point (in case operated by rodding), unlock any point (in case operated by D.W. or electrically), unlock level crossing gate in the route or the signal overlap portion unless the signal is replaced to ON. This condition is called route holding condition and ensures that the route set for a signal remains in tact as long as signal is Of.@9 Conflicting Signals to be loc"edIt should not possible to take of the conficting signals at the same time. The signals which can lead to head on collision, if cleared simultaneously are called conficting signals. Main signal and subsidiary signals cleared for the same route are also conficting signals. Whenever feasible, conficting points should be locked. ?9 Conflicting oints to be loc"edLocking for Home signal no. 3 is :Route Setting :-Setting of points - 8N, 11N, 22N, 25N Locking of facing points - 7R, 10R Level Crossing Gate - 6 N Conficting Signals :-Opposing Adv. Starter - 16Opposing Starter - 15Opposing Home - 27Interlo7>ing Ta=le"o7>ing Tra4& "o7>ing DogsThough mechanical interlocking is widely used, the main disadvantage with this locking is that the notches and dogs get worn out due to wear and tear. Hence they are required to be over hauled periodically once in 3 years. During the period of over hauling, the interlocking is disconnected and worked as a non-interlocked station, imposing a speed restriction of 15 kmph. The period of non-interlocking may vary from 3 days to 10 days depending on the size of lever frame.Trac" CircuitsTrack circuit was frst invented in the year 1872 in U.S.A. by William Robinson. Since this arrangement was very simple, nobody would have thought that the track circuit would make such an impact on signalling.Track circuit has become one of the most important safety devices in Railway signalling and has become an essential and integral part of modern signalling systems.The principle of track circuit is quite simple. The presence of a vehicle in a particular section is checked by passing an electric current through the rail from one end. If the current reaches the other end, then the track is clear. If any vehicle remains in the section, the wheels and axles of the vehicle will short circuit the current and prevent it from reaching the other end. Since the current is passed through the rails and rails form an electrical circuit, this arrangement is called 'Track Circuits'.Track Circuit consists of the following components :- 1) To ensure that the fow of current is restricted to a particular section, insulated joints are provided at both ends of the section. The insulated joints consists of insulating material made of Nylon 66, which prevents the fow of current between rail to rail, fsh bolt to rail, fsh bolt to fsh plate and fsh plate to rail of the adjacent rail joints.2) Rails of 13 m standard length are provided in most of the stations and they are joined together by fsh plates. The fsh plates do not provide reliable electrical connection and hence they are bridged by two mild steel wires to get good a electrical connection. These wires are called bond wires.3) The current is passed by means of battery (2v) at one end and current is regulated by a resistance.4) The current at the other end is sensed by a device called Relay.The relay used in track circuits is of a special design compared to the conventional electrical relay. A conventional relay works with a current or no current. But a relay used in track circuit has to sense a drop in current. Since we can not positively say that the current through the relay will be reduced to zero value when a wheel and axle occupies a track circuit, when the current through the relay reduces to 32% of the normal current, the relay should get de-energized. Such relays are called relays with high percentage release.The sleepers used in the track circuits should be of an insulating type viz. wooden or concrete sleepers. Cast iron or steel sleepers can not be used in track circuited section as they would directly short circuit the rails.Normally, the resistance ofered by wheel and axle of a train is about 4 to 5 milli 0hms which is almost zero. However, it is very essential to provide some factor of safety. Hence our, track circuits are designed in such a way that even when wheel and axle ofers a resistance of 0.5 0hms, the relay would be able to sense it. This provides a factor of safety of (500/0.5 = 100). This resistance of 0.5 0hms is called Train Shunt Resistance. Indian Railways is one the few world Railways who have adopted such a high train shunt resistance.It is stipulated in Signal Engineering Manual that the ballast resistance should not be less than 2 chms/km in station section and 4 0hms/km in block sections.For%etter Relia=ilit4 of Tra7> &ir76its)rainage H $allast Conditions needs to be goodAutomatic Warning at LC Gates- The following types of track circuits have been used on Indian Railways :-(i) DC Direct Current Track Circuit(ii) Alternating Current Track Circuit 50 C/S or 83-1/3 C/S(iii) High Voltage Impulse Types Track Circuits(iv) Jointless Track Circuits: AFTC(AudioFrequencyTrackCircuits)11.8.2 The most widely used track circuits in Indian Railways is Direct Current Track Circuits. Direct Current Track Circuits cannot be provided in sections with Direct Current Electric Traction like Bombay-Poona, Bombay-Igatpuri Sections. Track Circuits with Alternating Current at 50 C/S frequency is provided in these sectionsTypes of Track CircuitsSLOTTING AND INTERCABIN CONTROL Two important principles involved in slotting are (i)the slotted signal can be cleared only if all the controls required for the signal have been received.(ii) any one the controls should be able to independently replace the slotted Signal to 'ON' position.Lower Quadrant Outer (i) Outer lever (ii) Clearance of any one of Home signalWarner (i) Warner lever, and clearing of (ii) Outer (iii) Main Home (iv) Main line Starter and (v) Advanced StarterMain Home (i) Main Home Lever (ii) Main Line Track Circuit clear (iii) Control from other cabin (in case of two cabin working) SM's controlUpper QuadrantDistant 45 Degree any one of the Loop Home Signal90 degree Main Home SignalMain HomeSame as LQ Main/HomeEa10les of Slotte2 Signalstypes of slotting devices are used on Indian Railways viz. (i) Mechanical Slotting and (ii) Electrical slotting. Mechanical slotting can be used where there are only two controls for a signal. Two types of Mechanical Slotting devices are in use (i) Disenager - This is provided at the foot of the Home signal and ensures that the Outer signal can be lowered only after one of the Home signal arm is lowered to 45 degrees - 60 degrees. In case Home signal goes to danger, Outer signal is also replaced to 'ON' position.Three Lever Slot :- This is provided at Outer/Warner signal to ensure that Warner signal can be cleared only after Outer signal is lowered to 45 degrees to 60 degrees. Inter Cabin Control The clear standing room required for B.G. = 686 m. If a central cabin is provided, the Outer most point will be located at a distance of 423 m (686/2 + 100m. cross over length). This distance is beyond the range of rod operation. Hence if rod operation is to be adopted, two cabins are used, one at either end. With two cabin working, whenever Home signal is to be cleared, the overlap portion will be with the control of the cabin at the other end. A control from the other cabin is required to ensure that the overlap points are properly set and locked, before lowering a Home signal. Such a control is called inter cabin control. 'one slot one train' Control given by the other cabin and ASM/SM is valid for one train only. With the same control, the signal cannot be cleared for the second time, after the passage of the frst train. The control lever/slides have to be replaced to the normal position and again given for the second train. BLOCK INSTRUMENTSThe trains are run with space interval systems, maintaining defnite distance between two trains. The equipments provided at stations for ensuring space interval system of working are called 'Block Instruments'. Block instruments provided can be classifed into two categories viz. (i) Cooperative and (ii) Non-cooperative type. All single line token instruments (Daido Make and Kyosan make) are cooperative type. All double line block instruments and single line tokenless instruments with push buttons (Podanur Make) are non-cooperative type.Se56en7e ofO0erations