Sub-Inter Signal Distance.63 to 72

7/30/2019 Sub-Inter Signal Distance.63 to 72.

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63If the frequency of service is a constraint that can't be changed, we are left with a choice to eitherplace signals too closely or consider the "DoubleYellow"headway as goodenough. The secondoption seems to be better because you can any way achieve services very close to the desiredfrequency of service by propercounseling of Drivers.and subsequently try to improve on the running characteristics of the rolling stock (Le., Accelera-tion, and Deceleration)A substantial improvementcan however be obtained by reducingthe "Halting time" andthe safetymargin between theoretical and practicalheadwaywhichshould notpose a serious problem asthemakeupmargin isalsoavailable due tomaximumpermissiblespeedbeing 80 kmphas against thebookedspeed of 65 kmph.Let usconsider halting time be reducedto 15Secinsteadof 30 and let the safety margin to reducedby 15seconds (making the required practicalheadwayas 165seconds instead of 150secondsforachievinga theoretical headway of 180seconds)~henceTfreq =165& Th = 15ThusTs02:st = Tfreq - [Tr+Th+Tacc/ (TI+ov)]=165 - (5+ 15+42)=93HenceDs02:st= 4256+(93-52) x 18= 425 + 738= 1163 metersYou'can see the magical improement just by reducing the halt and safety margin to half of theircurrentvalues.Inpractice such exercisesare necessary to avoid to manysignals placed very clpse to each other,which does not only put a lot of stress on the Driver, but also reduces the reliability of the overallsignalling system leading indirectly to reduction in capacity.In fact it will always be wise to attach on more than one factors in the equation No.9, ratherthantrying to attach only one factor.Let usnow seetheplacement of signal501 &Sh,with 502 beingatdistance of 1163metersfrom ST

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~~ 42501 ~ ~~fI)~ 369m + 369 01 .. STATION

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As brought out on"P 25/26" the Shcan be located at Dbr, Le.,425 from St.Thus Dsh:st = 425 metersNowwe are leftwith 1163-425= 738mbetween$02 & 5h and we haveto located 501 in between.As brought out on P26 itcan be located exactly midwaybetween502, 5h Le, at a distance733/2= ;-369 = 370 meters from SH. This placesS01 at distanceofDs01:sh= 425+370 + 795 mwhich is > 550 meter andDs02:sh = 738 mwhich is > 550m or',

64

Thus satisfying the safety requirement of alternate signal being atleast Dbr ( for V max) awayfromeachother.Location of S03

As has been brought out on Page 29, equation 7 ( forSh being at > DbrfromSt)Case (1) where Tfreq has been increase to 165SecDs03:s02= [Tfreq-Tbr/(TI+ov)] xVbo-Ds02:sh= (165-42) x 18 -738 (Tbr/(TI+ov)=42from graph II Annex B, byinterpolation of stopping from 65 kmph)= 2154 -738Thus Ds03-s02 = 1426 meterBut as brought out on Page (16) No signal can be placed at more than 15D,hence :-Ds03:s02 = ISD = 700m (For 3 Min Service)

= 940 m (for 4 Min service)Case (2) Where Tfreq. is 150 sec only. As per P.29 Equn. (9) will be applicable (because Sh islocated at less than Dbr from St and distance between Sh & St is less than T1+Ov) : (Ref Fig 13)Ds03:50s2 = (Tfreq-Tbr(Full)- Ds02:st-Dbr)Nbo -Th-Tr-Taccl(TI+Ov)] xVbo=(150-52 - (623~425) - 30-5-42 ] x 1818=(150-52~1'~-30-5-42) x 18=(150-140) x 18Or Dso~:S02 =180meters

Whichshouldnot be allowedbecauseit is lessthan the train length. Howeverevenby. increasinghetrainhequencyto 155seconds,keepingallotherfactorsas theyare,the distanceDs03: 502 become acceptable, as can be seen below :-Ds03:s02 = [155 - 140] x 18270 metres

And by increasing train frequency to 165 seconds, it becomes perfectly acceptable as wehave already seen above. Thus in this situation, the only way to get an optimum signal spacing tosatis!y the need of very high frequency of servic~ is to sacrifice a little on the safety margin./: ., .


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65LOCATIONOFOTHERSIGNALS

As established on Page 30, and Page 17 & 18 all other signals can be placed at adistance ISD

a

SCHEME FOR MIXEDTRAFFICa) Running Mixedtraffic on the corridor Designed for EMUs

This signal placement scheme designed for EMU services, will be suitable for other types ofRolling stock and traction, if their speeds are restricted to match the braking distances.. For ex-ample the braking distance for the maximum permissible speeds of EMUs Le., 80 kmph was con-sidered to be 550 meters. Thus the signals will be placed such that at least 550 m distance isavailable between a double Yellow signal and a Red Signal. Thus if a vaccum brake, MaillExp Locohauled train is to be permitted to this route, its speed will have to be restricted.If the braking distance of the Mail 1Express trains is 1000 meters at a speed of 100 kmph, its speedfor 550 m Dbr can be.calculated as follows: -N550i2 = 550 (Because braking distance is proportional toLY100"Q..I 1000 the square of the speed. ,:V550/V1 0000 = Square Root550/1000orV550 = 100/0.55= 75 KMPH

Thus if Mail1Expr.esstrains are to be run on the same track, their Maximum permissiblespeed will haveto 75 kmph ( if Dbr = 1000meteratspeedof 100kmph). Similar Calculation can bemade for Goods or any other type of trains.B) Designing a Corridor & Scheme for mixed TrafficSince the running characteristics of different type of trains are different, no scheme can be designedto give the best frequency of service for all type oUrains. As brought out in (a) a~ove, if the scheme.is designed for best frequency of service EMUs other types of trains (with worse running character-istics) will have to run at reduced speeds.However, if the scheme is designed for the worst type of trains (Le, having minimum braking dis-tance), other trains can run safely at the maximum permissible speed, but with a reduced frequencyof service.For example of tt1e~mquirement of Dbr (at V max) is 1000 meters, then, the signals like S01 willhave to bea distance of ..000 m from St, otherwise S02 will not get a green aspect when St is Red, and if the distancerbetween S02 and St is less than 1000 m, ( which may be the case quite often)then even S03 willraot get a green aspect with starter Red. And if these distances, between St, Shs01, s02 etc., are increased, the frequency of service will reduceHowever, for the signals away t.iomstation since ISD is more, the conditions of 1000 m Dbr may getfulfilled automatically and Green headway will be available. But the frequency of Services willremain less, due to either higher distances between approach signals or due to non availability ofGreen headway.In these cases, it will be prudent to make a compromise, Le. to run the worst type of trains at somerestricted speed and cater for the braking distance oftype of trains for example the Goods trains can

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86be run at a restricted speed. while Dbr of Mail/Express trains can be the governing factor for display-ing of Green.Ifthe parameters of Loco hauled Mail/Express trains are put in Equ(4) for calculating the frequencyof service. it will be too poor to be acceptable to EMu services. On the other hand. if the frequencyis calculated as per the parameters of EMU's the braking distance of M/E trains will not be available.The second option is however, preferable. We should work out the scheme with EMU characteris-tics and then comply the conditions of availability of Dbr, between double Yellow to Red. wherever itis not available. if required. by repeating the double yellow aspect in the consequent signals. Theavailable headway can then the recalculated. to arrive at the practicable frequency of service.

EFFECT 'OF AWSAWS or Auxiliary Warning system etc., complies with the running characteristics of the trains.

For example. in the presently available AWs in.theMumbai suburban section, braking starts imme-diately after the trains passes. a Yellow signal. The speed is so controlled that after a distance of290 meters, the speed is clamped at 38 kmph. so that the trains can safely stop if the next signal isRed These parameters are programmable and can be changed at our will.But none of the signall ing schemes will have a very uniform signal spacing, with the result, that i fweprogram AWS for short ISDs it will consume too much of time running at restricted speed (Say 38kmph) after passing Yellow signal ( or whatever is programmed). On the other hand if it is pro-grammed for longer ISD'~ it will not be able to control the train safely for short lSD's. This followingFig. will explain this.77kmp

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38kmp 290m) ,~ t-I)~

I 120m IFIG -15.Thus this wjll have always to be compromise between better running and safety, until we have moreintelligent Aws. which will be programmed with the characteristics / ISDs of each every signal.individually and will apply a suitable braking curve to each signal differently.In any case, AWS can never be a guiding factor in deciding the placement of signals. it will have tobe programmed as per the requirement of the designed scheme.

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67SUMMARYOF FORMULASANDOTHER

IMPORTANTFACTORSTOBE BORN INMINDWHILEDESIGNINGA SCHEMEThe frequency of service of trains in an automatic section can not be increased beyond acertain limitswithout changing the "RollingStockCharacteristics" 11Halting patterns" "TrackStructure" etc.,the fequencyofservicecan be increasedby closespacingthe signalsonly toa limited extent.Theminimumfrequency ofservice (Le, Minimumtime betweenTrains)that canbe achievedis given by :-Tfreq = Tacc + Tbr+Th+ Tr+{Dbr+Dg:yy+Ov+ TI] - Dbr-DaccVbo Vbo

b) There is An Optimum Speed for achieving maximum frequency of service. This speed isdifferent from the maximum permissible speed of the Rolling stock.

c) The placement of four signals Le, Starter (St)Home (Sh), outer 1 (S01) and outer 2 (S02),has to becalculated. Separately,dependinguponthe scheme parametersand the restof thesignals can be placed at the generallSD ofthe Scheme.The following the formulas to be used for calculations of inter signal distance of vari-ous signals

a)

a) Starter signal (St)to be placedat the end ofthe Platformor the starting place for such trains (forwhich the scheme isbeingdesigned) on that stationsb) Home Signal (Sh)At Dbr (or ISD if Less) from St (This has to be less than Dbr only, if, the situation is forcing place-mentof So1at lessthanT1 ifyou placeShat Dbr; Inno casesh has tobe placedatmore thanDbrfrom St).c) First outer signal '(S01)Exactly midwaybetween S02 and Shd) Second outer signal S02)This has to be calculated as per the formulaDs02:st = Dbr +(Ts02:st -Tbr) x Vbo

The meaning of various terms has beendefined at various stages in the discussion. Theparameters will need that trial results for the RollingStock under consideration as are available inthe present case as per chart I AngexA&Be) Allother signalsAsperISDof theScheme,whichwill haveto becalculatedasbroughtoutonPage 13to19The ISOwilldepend onmanyfactors other than the desired frequencyof service alone I.

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r68

four aspectsignalling is ideal forautomaticsignalling. HigherNumberof aspectscanbeusedwith cab signalling or automatic train controlThe distance betwee'nalternate signals, has to bemore than the braking distance at Maxi-mum permissible speed, otherwise doubleYellowaspect will haveto be repeatedonconse-quent signals, instead of displaying green aspect in the nextsignal in rear of doubleyellow.The barestMinimumDistancebetweenthesignal shouldbenormallyT1+Ov. But incases ofn~ed, it can reduced uptoT1 only. This reductionwill not haveany adverse effect on head-way.

i)~)l'the signals neednothaveGreen Headwayavailable.The headwayrequirementof various~;slgnalss as followsSt - YellowSh - YellowS01 - DoubleYellowS02 - Green

All others - Greenj) With increasing need of high~r throughput there will be a need to modify RailwaysGeneralRules to eliminate or minimize the halt of 1" ( during day) and 2" during night for passingsignal at 'ON'. This should not be difficult since stopping of the train is ensured by deviceslike AWS (AuxilliaryWarning System.)The,basic ideaof these 1" or 2" stoppages isto makeit positively sure'that the Driver does stop & restart rather than continuing to moveat slowspeed. Stopping the trainand restarting is consideredas a signature of Driver being alert tothe situation.

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69

ANNEX "Au (Chart -1)

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ACCELERATION CHART (Chart 1);

Speed In Di$l- d Aa:.. Speed In Tn.. t taken InS:.I


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kina Chart (Ann 'IB"',Chart I )

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$P' '" KMPH Bkg.Te 1"FlIr1 Dao. Sp.!edIn 9IqJ.Ct&t.sec. Ml8Ia fTII$ Traedin IIIh$25 18 0-20 7 125- 0 . 0 -40 27 0.25 11 250o .. .. . -.. ..41 27 0.25 11 255. . ... ..42 28 0.25 12 260... '0..43 29 0.25 12 265. - - -44 30 0.25 12 270 '-"- '.. . .45 31 0.29 13 275- .. '..46 31.75 0.29 13 280,.47 32 0.29 13 285.. 290-8 33 0.29 1349 34 0.29 14 295f--- .-- ..50 35 0.33 14 300- . - ..51 36 0.33 14 310.. _0 ... ,-52 37 0.33 15 320.. .53 38 0.33 15 330. .....-.54 39 0.33 15 340- -\..55 40 0.33 .. 15 350-.. ",-56 41 0.33 16 360-.57 42 0.33 16 370- ..58 43 0.33 16 380.59 . 44 0.33 17 390r--' o .60 ,45 0.34 17 40052 - --65 0.39 18 425o.70 60 0.43 20 450o 075 70 0.44 21 500. 0 0 .. . . .. --80 80 0.46 22 550. . . ..


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Sub-Inter Signal Distance.63 to 72