sub-inter signal distance 52 to 62

7/30/2019 Sub-Inter Signal Distance 52 to 62.

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Situations of night where a halfof 2" andsobsequent speed of 8 KMPH is permissible, neednot beconsidered because for most part of the night the serviceswill generally be thinner than thepeak hours of the day,hence the gapswill beautomatically available)Thuskeeping a safety margin, of 100metersan ISOof 700 meters should be ideal for 3" service.ISD3" = 700 meterssimilarly ISOof 4" service will be : -IS04 = 240+21) x 15xO.28( - 100Safetymargin)= 1040-100ISD4" =940MetersHere is worth mentioned that it will be desirable to remove 1"x2" halts to make, before passing asignal on "ON". The train can stop and start. Also itwill bea great help to reduce the signalover:lapto bareminimum. This can be implemented onlyafter carrying out necessary changes in "GeneralRules"of Railways.This abovederivation puts an upper limits of ISO'sirrespective of other considerations.Havingseen the upper limits of ISOs, nowwe cah moveon to locate the other signals.Location of St1Earlier we have calculated the location of St1 as 1766meters from St.

However inview of the discussions about ISO,in a givenschemeto beviable, nosignal canbe placedat a distance of more than ISO,for avoidingbunchingof trains. Thus any signal, whosedistance from the adjacent signals works out to bemorethan ISO,will have to be placedat ISOHeresince the locationof the starter signal (St) isfixed,the locationof St1 will beat distance

ISO (Le.700meters fro 3" service or 940 metersfor 4" service)ThusSt1=700 meters (3" service)= 940meters (4"service)LOCATIONOF St2.

WMn the train starts at Starter signal St it accelerates to achieve its booked speed. Nor-mally itwiltachieve, or will be very close to achieving its booked speed by the time it crosses theSt1,which isat 700 meters fromSt ( for examplethe 9 coach EMUof Mumbai suburban takes 880meterstoachieve itsbookedspeedof 65kmphunderfully loadedconditions)Thus asperannexure"A", the-trainwIll cross St1 at almost bookedspeed (62) kmphat 715 meters as per Accelerationschart Igiven in annexure "A")

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@rI> I-I) rI> rI> I-I) I-I)I I I I I I I

!:TATION IFig 6


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53Hence the location of St2 and subsequentsignals will be as per the calculations for S05 toS08 as brought out on P-15 Le, equal to ISD of the Scheme.Thus Dst1:st2 = ISDThere will be situationswhere the distancebetween two stations may be such that it is notpossible to accommodate signals upto S04, S05 etc., and St2, St3 etc., In such a case the mini-mumnumberofsignals can beaccommodated,ad the placementhas to be asper the signalscloseto the stations on approach. (as we have seen that signals on departure side do not ask fordistances less than ISDs)Beforewe goonwith the placement of other signals on approach side, it will be pertinent todiscuss, the requirement of Number of Aspects. of signalling Le, 2 aspect 3 aspects or 4 aspectsetc.,

3 ASPECT OR 4 ASPECTSIGNALLING

Theoretically speaking, the driverof the train is requiredto begiven a signal, onlywhether hehas to STOPor Proceed. Inthat casewe haveto givehimonly a "Twoaspect signalling" Le.,Red& Green, but in that type of two aspects signalling, the Driver-is under a great pressure as heapproached a Stop signal which is without any warning. This was resulting in the drivers makingmistakes of passing the signals onON and also they had a tendency to slow down the train whileapproaching thesignal, resultingin loweraveragespeed of trains.

Thus itwas considered necessary to givean advancedwarning to the Driver in the formof a.Yellow Signal" which tells him to : proceed cautiously up to the next signal". This has resulted indeveloping a better confidence in the Drivers,finally givingway to more safe and efficient driving.Itwas also considered reasonableto give the trains, a full braking distance after the cautionaspect (yellow signal) upto the Red signal. In cases where this full breaking distances was notavailable at fourth aspect Le., "Double Yellow' was added to provide this full baking distancebetween the doubleYellowand Red signals. This Principle is strictly followed in Automatic Signal-lingTerritories.( Inother than automaticsignalling, this principle is followed in a little differentman-ner, the details of which are out of the scope of this article.Thuswherever the full breakingdistancefor the typeof Rolling stock inquestion isavailablebetween Yellowand Red signals, a DoubleYellow"signal is not required in automatic signalling.Thus thesignalling schemecan be predominantly3 aspectwith4 aspects signals placedwhereverthe situationdemands due to non-availability of full braking distance.However itwill beseen that with high frequency of services, the number of4 aspects signalswill be quite large nos, rather than being exceptions. Also the 4 aspects signaling will have the

followingadditionaladvanta~s :- -1) Fusingof Greenaspectwillswitchondoubleyellowaspects instead ofyellow,and therefore,signalwill be less restrictive permitting higherspeeds.2) Fora higherfrequency ofservices ifgreenheadwayisnotpractically possible, atleastdouble


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yellow headwaycan bemadeavailablewhich will be better than yellow.3) This permits yellow aspect to be placedat lessthan the braking distance, wlthout which thesignalling scheme may notbe feasible manytimes.4) It will be much easier to place a "Double Yellow"Signal at braking distance, rather than"Yellow"because "Yellow"only will lead to unacceptably higher inter Signal distances fromthe point of view of headway.5) The Signallingschemewillbe normallydesignedwith Breakingdistance at Bookedspeed.In3 Aspects Signalling since there is only signalYellowsignals, the Braking distance will haveto beconsidered for maximum permissiblespeed, otherwise the ISOwill notbe adequate tosafelystop the train, short ofa redsignal after passingaYellowsignal atVmax. This problemget automatically solved in 4 aspect signalling, because the Dbr for V max isto be ensuredbetween DoubleYellowand Red aspectswhich ismucheasily possible.Considering the above facts, in all our prudence, itwill be desirable to go for a uniform four aspectsignalling rather than having a 3 aspect signalling witha number of 4 aspects signals.

HIGHER ASPECTS SIGNALLING (5 ASPECTS OR MORE)More number of aspects on the signal? may be a "Triple Yellow" or a combination of "Green &

Red" or a different colour altogether, will give a advance -advanced warning to the Driver. But thenthe number of signals will became a littletoo many,spaced, at very short distances. The advan-tages in runningwill bemarred bythe increasedstresson the Driver. However,such higheraspectscould beuseful when the speed control of the trains isautomatic through the signalling informationgetting directly conveyed to the speedcontrol device in the train.Forthe manu.alspeed controlled trains, the 4 aspects should beconsidered to be the maxi-mum required.

Now let us get back to our calculationsof placement of signals.LOCATIONOF502Havingdecidedthat we have to go for 4 aspects signallingscheme, let's getdownto bebusinessofcalculating the distances for the placement of other signals ( A similar approach can however beapplied for 3 aspects signalling if required)

Let us first find out the location of S02 which isthe first signal in Rear of the stations, whose "Green

1805 I

I STATION I

. Fig 7


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Headway"(RefFig-?above) is requiredto beconsidered.Timeavailable for travelling from S02 to Stwill be :-Ts02:st = Tfreq. - Time requiredfor travellingthe distance,past the overlap of St1, after haltingTs02:st =Tfreq -(Tr+Th+Taccl(Tl+ov),whereTfreq =Time as per frequency of serviceTr= Reactiontime 5 secondsTh = Halt timeTaccITl+Ov)= Acceleration time of train to clear to overlap of the train lengthTherefore,Ds02:st = Dbr+(Ts02;st-Tbr) xVbo

no (Equ.6WhereDbrt = Breaking -distanceTbr = (breaking time)Vbo = (Booked speed)(Considering that the distance will be more than the braking distance, as we can not earlier a "GreenSignal" at less than the braking distance from a "Red Signal", as explained earlier. ( infact thedistance between double Yellow to Red has itself to be equal to or more than the braking distance)}LOCATION OFSh :-

Afterdeciding the locationm S02,the locationof twointermediate~ignalsLe.S01andShcanbe decided. Leus firstsee about Sh:-.As per the derivations in previoussections,the distance between S02 and St can have twopossibilitiesi) Ds02:st > 2 Dbrii) Ds02st < 2 Dbr > Dbr

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J STATION I

FigS


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Headway"(Ref Fig-7 above) is requiredto beconsidered.Time available for travelling from S02 to Stwill be :-Ts02:st = Tfreq. - Time required for travellingthe distance,past the overlap of St1, after haltingTs02:st =Tfreq -(Tr+Th+Tacc/(TI+ov),whereTfreq = Time as per frequency of serviceTr= Reaction time 5 secondsTh = Halt timeTacclTl+Ov) = Acceleration time of train to clear to overlap of the train lengthTherefore,Os02:st= Obr+(Ts02;st-Tbr)xVbo

... (Equ.6WhereObrt = Breaking -distanceTbr = (breakingtime)Vbo= (Bookedspeed)(Consideringthatthedistancewill bemore thanthebrakingdistance,as we cannotearlier a "GreenSignal" at less than the braking distance from a "Red Signal", as explained earlier. ( infact thedistance between doubleYellowto Redhas itselfto beequalto ormore than the brakingdistance)}LOCATIONOFSh :-

After deciding the locationaof S02, the location of two intermediate signals i.e.S01 and Sh canbe decided. Le us first see about Sh:-.As per the derivations in previous sections,the distance between S02 and St can have two

possibilitiesi) Os02:st > 2 Obrii) Os02st < 2 Obr > Obr

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[!Ut*) t*) t*) t*) t*) t*)I-STATION I

FigS


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56I) Ds02:st > 2 Dbr

Infirst casewhere Ds02:st ismorethan2 Dbr,theHomesignal Shcan be locatedatDbr fromSt or at ISD from Stwhichever is less. This is because, if there is no other consideration, there isho point in placing signals too closely,and placinga signal atmorethan Dbr from the Stwill causeunnecessary increase inthe running time betweenSh & St. The distance between St& Sh is theonewhich includesstopping, haltingand restartingof thetrains, involvingmaximumtime consump-tion.II) Ds02:st < 2 Dbr > Dbr : -When the distance between the Green and Redsignal is less than 2 Dbr,whether the signal Shshould beplace at less than Dbr from St ?

"No" because the "Green Headway"of S02 is already available and placement of Sh doesnot affectthisheadway.S02hasalreadybeen placedat themaximumpossibledistancefromSTforgetting the desired headway ( However such situation i.e., Ds02:st Dbr will not normallyarise if green headway of S02 isavailable). Thus inbothcases,the homesignal Sh has to beplaceat Dbr (or ISD if less) from the Starter signalSt. Howeverif this leads to the placement of S01 at


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1) Whenthe train has crossed the nextsignal itwillnotclear the overlapkeepingthe rearsignal also at Red.Thiswillbe particularlyharmfulin case of 801 where the haltingtrain (at 8t) willkeep S01 at Red, fora longtime2) Itwillmean placing signals too closely,creating confusion to the Drivers.Nevertheless ifitbecomes necessary to place signals at less than "T1+Ov"due to headwayrequirement,theycan be placed so,whichwi!resultinoveralladvantage in running.Letus see how.Let us assume that the distance "Ds01:sh"is less than "T1+Ov",inthis case when a train isat the footof8h, the signals 801 and 802, bothwillbe Red. Butsoon after when the train clears theoverlap beyond 8h inits normalcourse of running801 &S02 willclicksimulteneouslyto becomeYellowand DoubleYellow.Thus S02willclear faster to doubleYellowas compared to the situationwhen" Ds02:sh" is more than "T1+0v", as the train willtake more time to travel, this" more

distance" in itsnormal course of runningdemanding highe"rheadway. Forexample:-

~I-I) ~~I~~ ~I-I) ~~JI. I JI ...~ 120mov I-+t (STATIONFig 10

In case (A)the distance between 8h &801 is 2450m and in case (B) it is 320m. With a train lengthof 200 meter and overlap of 120 meter, in case (A)the Ov past So 1 willnot be cleared when a trainis at the foot of Sh, whereas in case (B) itwillbe cleared.The clearance of 802 tt'Double Yellow"willhowever, depend on clearing the Ov past Sh, whichwillbe faster in case (A) bE/cause of shorter distance between 802 to 8h. Only in situations of a holdup of a train at 8h we willbe at a loss, because 802 willremain Red, in addition to 801 which couldhave became Yellow in case (B). However, case (A) will be of overall advantage ifthe headwaydemands such a situation, as hold ups of Sh willbe very rare and otherwise we willhave to go forcase (B), where itwill not be possible to achieve as low headway as in case of situation (A).THE BAREST MINIMUM DIS'JANCE BETWEEN SIGNALSAs per the above consideration, ifthe distance between 801 &8h comes to less than the trainlength, Though as agreed above, itwillstill result in some running advantage, it should not beaccepted because inthat situation there willbe fortoomanysignals, than the driverof a train canhandlewithease. Thus noplacement ofsignalat a distance of"less than the train length"shouldbeacceptable.

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58In such a case either the requirement of frequency of service should be relaxed or the runningcharacteristics of the rolling stock should be improved, rather than placing signals at less than thetrainlengthdistances. .LOCATIONOFS03

~~ ~~ ~~ ~~ ~~ ~~ ~~STATION

FIg11This signal should be located at a distancewhich gives a " Green Headway" equal to the requiredheadway,as per the frequency of service, which can becalculated as follows:-Ds03:s02= [Tfreq.-Ts02:sh+Tbr/{TI+ov)]xVbo(Time reqd.for braking from s02 to Sh& Clearing itsT1+ov)Because the train will be travelling at its bookedspeedbetween S03 & S02 and will start retardingwhile clearing / approaching Sh so as to stop at St, There can be two situations:-1)As discussed earlier the locatiofl of Shwill be at Dbr from St, in that caseTs02-Sh = Ds02:sh Because the train will start braking onlyVbo at Sh, till then it will run at VboThusDs03:s02 = [Tfreq -Ds02:sh - {Time takenJor travellingfirst 320m (T1+ov)Vbo by the train while braking from sh}] XVbo(This will have to befound from graph, likethe one inAnnexure B)= [Tfreq. - Tbr / (T1+Ov) - Ds02:sh] x VboVboOr - :-,;Ds03.s02 = ["(freq-Tbr/(T1 +Ov)] x Vbo - Ds02:sh

(Equ.7)2) IfSh Is located at less than Dbr from St thenVbowill be applicable for such distance.Ds03:s02=[(Tfreq.-Tbr/(TI+Ov+Dbr-Dsh:st).. .(Provide-dDsh:st is more than T1+Ov) -Ds02:sh - (Dbr -Dsh:st)) x VboVbo

... Equ.8)(Pr9vlded Dsh:st Ismore than TI+Ov)

In case Dsh:st is less than TI+Ov, the equations will be modified to : - .

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Ds03: s02=[ Tfreq- Tbr(full) - Ds02:st-Dbr -Th-Tr-Taccm+Ov)] x VboVbo on Eq9

Becausewhen the train stops at St, the overlapof Shwillnot get cleared resulting in S01 remainingat Red. Thus S02 will remainYellowand S03will remaindouble yellow till the time the train startsagain and clears the overlap of St.(Here (Dbr-Dsh:st) is the distance by which the Dsh;st is less than the Braking distance)This is how (D503:so2) can be calculated in this case, however as discussed earlier there should not general lybe any occasion where Sh is placed at less than Dbrfrom St, as itserves no purpose, except in cases where,the distance between Sh & S01 becomes < T1, if Sh is placed at Dbr from St.LOCATION OF So4

~~ ~~ ~~ ~t:I) ~~ ~~ ~~STATION

Fig: 12804 should be locatedat the headwaydistance from801. The trainwilltravelat fullspeed at804, So3

& S02, but the speed at orafter So1 willdepend upon the locationof Sh & S012. IfSh islocated at DbrfromStthen braking willstarts only atsh,thus S01 willbe passed atfull speed leading to Ds04:s03) = ISD asperthe ISD ofthe scheme as discussed earlier. But if Sh is locatedat less than Dbr from St ( which should notbe the case, normally as explained earlier) Then after passing S01, and before reaching Shsomewhere inbetween Le,at Dbr distance from startersignal St,the trainwillstart braking, and ifthe distancebetween801and Sh is not much, the train may actually start retarding before clearing the overlap of S01, giving risetomore time consumption

However, on having a dose look at the braking cnart and graph in annexure "B", it is clear that atdistances close to Dbr the difference in speed is very less for considerable distances, therefore for allpractically purposes, itcan be assumed that the train will travel past 801 at full speed.

During the actual placement of signal on the field, a lot many other factors like non availabil ityof proper space or "track centres", ( The minimum distances from the tracks for erection of thesignal, so as to comply with the schedule of dimensions for elimination any possibilities of infringe-ments of the signal from the running trains.). Or the problems of visibility, or the encountering ofdiversions etc also come into play, which necessitates a little variation in the distances. Thus theerror caused due to the assumptions that train will travel past S01 at full speed will be of no practicalsignificance. .

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CONSIDERATIONFORMAXIMUMPERMISSIBLESPEEDFORCALCULATINGBRAKINGDISTANCE

Beforewe proceed further a point to note 'is,that, in case of late running of trains, they arepermitted to travel at a higherspeed,than Vbo,calledmanimumpermissible speedVmax)which inthis case is 80 Kmph. Now the question iswhether we shouldmakeour calculations basedon theparameters (Dbr,Tbr etc.) for Vmax orVbo. The two factors to be considered are:-1) Todecide this, let us referto "P-7/8"where it has beenbrought out thatmaximumfrequencyof service is obtainedat anoptimumspeed ratherthan themaximumpermissiblespeed. Thescheme has to be, therefore, designed for a booked speed which should be close to theoptimum speed. If the trains run at other speeds, which may be more or less than the

optimum speeds, the frequency ofserve will suffer. Thuswe should baseor calculations onthe parameters for bookedspeed. '2) The secondquestions isconcerningsafety. Ifthe scheme isdesigned, forVbo and trains runat V max, then whether it will be possible for them to stop within the braking distancesprovidedas perVbo.

For ensuring the safety, it has to be ensured that after the first warning signal (Le, DoubleYellowin case of 4 aspect. signalling), adequatebrakingdistance is availableto stop the train fromVmax. This will be generally,automatically achievedwhen we design our scheme for four aspectsignalling. However if we like to go in for a 3 aspect scheme the "ISO" can not be less than thebraking distance at Vmax, which will pose serious problems in the placement of signals in thevicinity of stations on the approachside.

Thus during the design of scheme, it has to be ensured that, the distances between any first& 3rd signals in not less than the brakingdistanceV max. The situations will be normally automati-cally met. But in case it is not met the Ilird sigaror may be 4th signal also will have to be kept atdoubleYellowinstead of Green.(Though for the design of the scheme as such, the braking distance at booked speed should beconsidered, because trainswill be normally runningat bookedspeed.Next we willconsider a sample case to further enhance the understanding of the concepts.

A SAMPLE CASE STUDYLet us calcuiate various inter-signal distances for a station in Mumbai-Kalyan section insuburban corridor; from the date collected, as per Annexes "A" & "B"

a) DATA :The-main data are .Tr~in length = 9 coach = 200 meters ( Actual 195 meters)Booked speed = 65 kmph = 18meters/secMaximum permissible speed =80 kmph.


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Halting time = 30 Seconds at small stationsReactiontime = 5 Seconds(OfDriver)Overlap distance = 120meters.

Acceleration = As per chart I & Graph I and II in annex "A" (Results of trials conducted for fullyloadedconditions duringpeakhours)Deceleration+ As per charts & graph I & II inAnnx "B" Requiredfrequency of service = 3 minutes= 180SecondsPracticalheadway required 150SecondsFREQUENCYOF SERVICEFirst of all, we will have to check whether with the given data, the required frequency of service ispossible or not. Referring to P4,5& 6. The frequency of service is given byTfreq =(Tacc+Tbr+Th+Tr)+(Dbr+Dg:yy+Ov+ T1) - [Dbr+Dacc]Vbo VboWhere apart from the parametersdefined in (a)above:-Tacc :Acceleration time to achieve booked speed after starting= 78seconds (fromGraph-I)Dbr = 425 meters (brakingdistance atVbo, fromChart I -AnnexB)Dacc = Distance travelled beforeachieving bookedspeed from starting = 880 metersTbr = Braking time to stop fromVbo= 52 secondsThusTfreq ( 78+52+30+5)+ (425+340+120+200)-(425+880)18 18orTfreq = 165 + 1085-1305 = 165 - 220~8 18

:{Traln freq. =153 seconds}Which means that a frequency of 153 seconds, and hence that of 180 seconds practically is

possible, with the kind of date above Le., the present EMU stock with 9 coach rakes, by placing thesignal 502 at a distance of 340 meters from S01.

However using the same rolling stock to from 12 Coach rakes will increase Tacc, Tbr, and ITrain length - thus achieving 1~Oseconds ( or close to that) headway will not be possible. Exactcalculation can be made by conducting trials and generating charts as in Annex "A" & "B" afresh.LOCATIONOF S02. S01'. & SH:-Befqre deciding the Location of S01, we have to decide, that of 502. As explained on Page 23 let usfind out the location of 502 with respect to 5t first.Ds02:st= Dbr + (Ts02:st - Tbr) x Vbo ... (Equ.10)

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62Where Ts02:st = Tfreq - (Tr+Th+Taccrr1 +ov)}substi tuting various values from the data given in (a) we have: -Ts02:st = 150 - (5+30+42) ...(Taacrr1 +ov) =42sec from Chart-I annexure -A)63 SecondsTbr = 52 See (from chart IAnnexure B braking from a speed of 65 kmph)Vbo = 65 kmph = 18m/seeDbr = 425 metre (from chart II for stopping from 65 kmph.)Thus we have Ds02:st = 425 + (63-52) x 18 = 425+ 198OrDs02:st =623 metersThus S01 & sh are to be accommodated in 623 meters and if Sh is placed at Dbr Le, 425 metersfrom St, the distance between Sh & S02 will be only 198 meters in which case So 1has to be placedmidway, Le., at a distance of 99 meters from Sh & S02As has been discussed earlier (p-26 to 28), the minimum distance between signals should not beless than "T1+Ov". which works out to 200+ 120 = 320 meters in this case, and under no circumlstances, it should be less than the train length itself Le., 200 meters in this case).Thus if there is no other alternative, location of Sh has to be compromised, and it can be located aunder:

659m

~:H8:8J: ~f4 524m~~

r-+~ ~ ~~I

~~STATION

Fig13OnemoretJltingo be ensured isthat the S01 is placed at more than 550 meter from theSt ( at 80kmph the Dbr = 550 meter reference Chart I Annx,"B",) Otherwise S02 will also haveto be keptadouble yellowwhen St is Red,whichwill meanNonavailabilityof Green Headway of S02. Inthacase, distance between S02 and S01 will be 659 -550 = 107meters, which is not allowed. It withus be necessary to increase the headway requirement (Le., reduce the fequency of service)0consider "DoubleYellow"headway as good enough (insteadof Green) for running of trains, whicmeans that in the normal flow of traffic driverwillJarelysee green aspect of signal S02, mostlyhewill have to maintain his normal speed etc., on doubleYellowaspect of Signal S02.

sub-inter signal distance 52 to 62

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