US2333963A

US2333963A - Railway traffic controlling apparatus

Info

Publication number: US2333963A
Application number: US474107A
Authority: US
Inventors: James J Van Horn
Original assignee: Union Switch and Signal Inc
Current assignee: Hitachi Rail STS USA Inc
Priority date: 1943-01-30
Filing date: 1943-01-30
Publication date: 1943-11-09
Anticipated expiration: 1960-11-09

Description

Nov. 9, 1943. J. J. VAN` HORN 2,333,963 Y. RAILWAY TRAFFIC cm'iTRoLLINGv APPARATUS Filed Jan. 50, 19454 3 Sheets-Sheet l L, www. SEEN bwk AIWIEA www NOV- 9, 1943 J. J. VAN HORN 2,333,963

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Jan. 30, 1945 5 Sheets-Sheet 2 m u Y j@ aya/'xm J. J. VAN HORN RAILWAY' TRAFFIC CONTROLLING APPARATUS i Nov. 9, 1943.

Patented Nov. 9, 1943 RAILWAY TRAFFIC CONTROLLING APPARATUS .lames J. Van Horn, Pittsburgh, Pa.,A assignor to ThcrUnion Switch & Signal Company, Swissf vale, Pa., a corporation of Pennsylvania Application January 3o, 1943, serial No. 474,107

5 claims. (o1. 246-33) My invention relates to railway traiiic controlling apparatus and is particularly directed to the control of traiiic in a single lor double track, two-.direction system of signaling. More specifically, my invention relates to the control of traffic and of the opposing signals between two interlocked locations in such a system by means of a coded line circuit.

Oneobject of my invention is to provide trafc locking betweenl a mechanically locked machine and a. non-mechanically locked machineA over a coded line circuit. Another object is to provide for traic direction selection over the line circuit and for maintaining the established direction until this direction is reversed by the operator. A further object is to provide control for two proceed indications of the opposingheadblock signals. A still furtherv object is to simplify the line circuitV control and. adapt it to a stretch of track having no intermediate signals. Other objects. purposes and characteristic features of the invention will become apparent fro the description which followa Y I accomplish the foregoing objects as follows: by employing a series relayV at: the feed` end of the line circuit and a polarized control relay at the receiving end of the line circuit; by transmitting code continuously over the line circuit so as to provide a channel for feed-back code at all times; and by polarizing both the normal contro-l code and the feed-back code.

I shall describe three forms of apparatus em- Vbo'dying my invention and shall then point out the novel features thereof inclaims.

Fig. l of the ac'companyingdrawings is adiagramxnatic view showingone form of apparatus embodying my invention. `Figs. 2 and 3 are diagrammatic views showing modified forms of the invention shown in Fig. 1 and also embodying my invention. Figs. la to le, inclusive, are circuit diagrams sho-wing vcontrol circuits Vfor certain of the apparatus shown in Fig. l.

Similar reference characters refer to `similar parte in each of the several views.`

Referring to Fig. l of the drawings, I have shown a stretch of double track having a number ci cross-overs and having a passing siding PSI at one end and a passing siding PS2 at the other end of the stretch. Both tracks of this stretch are arranged for traffic movement in either direction, as indicated by the

signals

2R and 8L vfor' the upper track, and signals ER and |2L for are westbound leaving signals;` and signals 8l=t^h 4and IZR are eastbound leaving signals. Although two tracks are shown in order to illustrate a wider application of the invention, it will be understood that the two passing sidings PSI and PS2 could be associated with but one track, such as the upper track, for example. Associated with each end of the stretch is an interlocking machine which, at one end, may be a mechanically locked `machine andy at the other end, a nonmechanically locked machine. c

The upper and lower tracksshown conventionally as single lines in the drawings, are dividedfinto track circuit sections by means of the usual insulated rail joints and there is a source of current S associated With each track circuit at one end thereof and a track relay TR associated With each track circuit at the other end thereof. These' current sources and track relays Vare shown conventionally in orderto simplify the; drawings. Only the upper track is shown subdivided into a number of track circuit sectionsfbut it is apparent thatfboth tracks could be similarly arranged. A contact of each of the track-relays is -included in the line circuit.l

At one end of the line circuit is asource of current having the terminals B-C which supplies current of onefpolarityV or the other according as the traino direction selecting or trailic stick relay' ylEFS ;is energized or deenergized. The polarized line current is coded by means of the code transmitter lCT and maintains polar relay A at the other end of the line circuit operated to its one or its other position in accordance with line current polarity. The polar biased code following relay CF follows the line current code impulses and operates on line current of either polarity provided however that the polar contactsl of relay A agreein position with this polarity. That is to say, when both the line circuit polarity and the contacts of relay A are reversed, the current polarity supplied to relay CF remains the same so that the relay continues to operate. Current of wrong `polarityin the winding of relay CF will cause the armature of this relay to be held more firmly in the deenergized position against the armature backstop.

Code operation of relay CF energizes the decoding transformer DT and causes code operation of the impulserelay IR which under proper conditions delivers impulses of a feed-backcode to the line circuit during offV intervals inthe mastercode to which yrelay CF is responding. This rmannerof operation of relay IR is well known and is shown,-ior example, in the United Y `States @Reissue Patent No. 21,783, granted to Herline circuit by relay iR at the otlier'end, relay Dwill follow code and will maintain the slowVV pick-up slow release traffic relay IEF energized.`

As will now be apparent, the line circuit Livr-L2 provides a channel for effecting intercontrol loi the apparatus vat the two vends of the stretch. By constantly operating the `coder 15CT,a circuit for the return of feed-back code ispalways. available Whenever the stretch is unoccupied.

Also; bypclarizingthe master code,rcontro1 overA two proceed indications is provided for the headblock signals attach. end, Reny lint-.and lIWF are traffic locking relays and will 4normally both be energized when the stretch isunoccupied and vall -oi'the signals are at stop,-as illustrated in the drawings. Y

To line upa route' from right to-left orwestv`bound, trailic direction stick relay` IEFS is ilrst energized so as to reverse the line circuit'polarity. This will cause polar relay Afto reverseand to j yopen its contact 24 so as to release the westbound Ytraillc locking`r relay IWF and thus prevent 4the Vclearing of an eastbound route fromleft to right.

Althoughf relay IWF `is released, relay CF'con- I `tinues to iollowV code and to operate relay IR so that the feed-back circuit is effective for operating the yseries relay D which maintains the eastbound traiiic locking relay' IEF energized. When a route isV set from lei't toright, or eastbound, the trafllc direction stick relay IWFSiwill 4be energized so that the feed-.back circuit for relay D will be opened. "Ihe continued release of, relay D will'cause traffic locking relay IEP' to `release which prevents the clearing of a westbound route.

Referring for the moment to Figs. 1a and 1b, "these figures show the control for the trailic direction stick relays IEFS and I WFS. respectively. Included in the circuit for relay IEFS is acontact *of relay 'IES which is controlled over the circuit shown in Fig. 1c. Similarly, the relay SWS-which enters into the control `of relay IWFS has a control circuit as shown inY Fig. ld. The latterV figure also shows 4the signal levers and 'switch levers` i'or the mechanically Alocked matwo ends ofthe stretch. The control circuits of Figsla to le, inclusive, are well known and .are shown merely to render lthedisclosure more coniplete. The nomenclature used and manner of showing of the various elements in these circuits is conventional so that no detailed descriptionof ythis `portion off the apparatus appears'necessary.

Y Returning again to Fig. l for amore detailed descriptionof'the operation, normally, with the i directional stick relay IES energized and the tramo-stick relay IEFSbdeer-iergized, asshown, current-will'ilow from one terminal B of a suitable source, overthe back point ofcontact I6 of relay IEFS, irontV point of contact YII of relay ATES, -front 'point oir 'coding-contact Il 1o! I'coder 15CT, line wire LI, front contacts I8 to 23, in-

elusive, of the interveningV track relays,` baci: point of contact 25 of impulse relay IR', winding n of relay A, front contacts of the varioustrack relays, wire 26, and

contacts

21, 28, and 29 of coder 15CT and relays IES and IEFS, respectively, to

the other 4terminal C or the .same source.; Under this condition, the line circuit will be ycneirgfizecl with coded current of` what I shall term ynormal ,relative polarity so that relay A will maintain its polar contacts closed in the left-hand'position, as ,shown.' Relay CF will accordingly vbe energized tified over contact 32 of relayCF in the usual manner.` Alsorsincefrclay CF is ifollowins'code,

:the impulse-relay -rIRwul likewise follow -bemg picked upwhcnthe hacky point of kcontact 33 is closed, and released lhenz-theimtmoint `of :this contactis eloaemM-fuiiy explained-'in the "K above BlosserUnitedStateo patent.

`If at this time, .nieuwe isf exercised ancrelay IWFS is deenergized soitht'frontroontoct and back contact I0 are both closed. an impulse of feed-amel;v code will be delivered totheline circuit each timethot the front point of contactV 251 of relay IH.` becomes` cloned. 5 4'Since the Ybeck pointof contact II 0f coder l'ISC'iIL is 810m ttul'-V r'ing the time when the Iced `back impulaese effective, relay D will be: energized. by :eenmaal: code and will follow this code. r The polarityot Vthe feed-back code' canne properlyselected with respect to thepolar bias ot relay'D'so'thd this relay will operate only whenA leed-back.. code; of the proper polarity-is present inthe linecircuit. Code operation oi' relay'U causes relay IEF to become energized over` `fronti contact 84." Accordingly, with theapparatu'sinits'noimalfcom dition, relays IEF 'and'IWFiy will botlibe-enerygized so'that signal ILv or HL `may be cleared for a Westboundmove, or signal ZRorGR may f be cleared for an eastbound move. The conventional circuits for the control of the respective .home relaysior thesesig'nals are shown in Figle and willbe clear without detailelddescription.

Assuming "that signal lltisythe onewhiohis cleared, then relay me wm be deenergizedvtngre by the polarity of the line circuit will-become reversed through the ,closing 0f the` back points of contacts I1 vand 2 8. 'Polar relay A will-now reverse, opening the circuit for relay IWFat its .v

contact Y24, thuscausing this relay to Since relay IWF lhas its front contacts inthe control circuitsfor the eastbound Signals ZRand 6R, these signals cannot bev cleared Vior an eastbound move'opposing thatestablished by y theclearing of westbound signalL. The line circuit, accordingly. provides .traffic lockingwhich comes into playV when a headblook signal for a givendirection is cleared. r

Reversal roi? polarity of `the `master code in the 'y line circuit thuscauses relay iWFto release,l

but the polarized .relay VCF' will continue to'ope cratel under this condition. Since relay IWFS remains deenergized and relay SWS remains energized, the feed-,back .circuitjover contact 2l of relay IR will continue effective with a'reversal of `master coolev polarity. Accordingly, relays D j and IEF will be energized. The .cnergization of, .I

relay IEF provides block` controlfor signal 8L when this signal governs a move past signal 8B.

When relay IES is deenergized and relay IEF is energized, relay IEFS shown in Fig. 1a will be energized over an obvious circuit which includes contacts 35 and 36 of these respective relays, and will provide a call-on aspect; for a following move past signal 8L, when desired. Relay IEFS will remain energized over its stick circuit which includesthe back point of contact 35 `of relay IEF, wire 31, and the front contact 3820i relay IEFS. With relay IEFS picked up, the polarity of the master code supplied to the line circuit is the same as under the f previous condition when relay 'IES was assumed deenergized, 'thus preventing energization of relay IWF so that this relay cannot permit an opposing move until relay I EFS becomes deenergized. This will occur only after the train vacatesthe stretch and relay D again 4responds to feed-baci: code and energizes relay IEF. If traffic had been established in the reverse direction, then relay '3WS would be released so that the feed-back circuit would be open at contacts 39 and 4D whereby locking relay IEF would be released.

summarizing the operations des'crihedso far,

`normally when the stretch is unoccupied, master code of normal polarity will be eiiective in the line circuit tov operate locking relay IWF and feed-back code will be effective to operate locking relay IEF. When a signal is cleared to establish a given traic direction, either the polarity of master code is reversed, or the feed-back circuit is rendered ineiective sovthat in either case, the locking relay forthe opposing traffic direction is deenergized so as to lock out all traiiic movement in that direction. It will he noted that as shown in Fig. ld, the control circuits for relayfSWS include contacts 4I and 42 of signal lever repeater relays ZRLP and'SRLP which, in turn, are controlled over the iront contact 43 of relay IWF. Accordingly, these repeater'relays can be energized only if master code 'of proper polarity is effective which corresponds with Westbound traflic and which means lthat signals Bland I2L are atstop. g y

Referring now to Fig. 2, the apparatus of this gure is similar to that of Fig. -l kwith the eX- ception that instead of polarizing the master code, the selection is obtained through the .use of two code speeds as, for example', 75 and ,180 interruptions per minute. The. code transmitting relay CTM repeats the code which it receives and transmits this code as master code tothe line circuit over its front "contactgt For eastbound trafc, with relay 'IES energized and relay IEFS dee'nergized, the; master code 'is iii() which corresponds to that condition in Fig. l in which master code of normal relative polarity was supplied to theline circuit.'` Relay CF at the other end of theline circuitwill follow the 180 code, energizing the'decoding transformer DT which causes energization of'locking relay IWF through the resonant rectifier unit ISBDU in the usual manner. This unit is so tuned Vas to cause operation of relay IWF on 180 code but not on '75 code. Impulse relay lRwill operate at 180 code and will transmit feed-back impulses of this code to the line circuit over its contact 45 for operating relay D at the other end. Operation of relay D will cause the locking relay IEF to be energized.

If signal 8L is now cleared,v relay 'IES will be released so that the master code will be changed from 180 to '75 at the backpoint of contact 4B vof relay lES. Relay IWF will now release to provide the lockoutV protection 'but relay IR will operate at the '75 code rate so as to maintain the feed-back circuit effective for nkeeping relay IEl1 energized. 'The deenergization of relay 1BRS causes the energization of relay IEFS so that relay CTM will continue to cause master code to be applied to the line circuit after relay lES becomes picked up. This occurs when the train vacates the track section IT'and approach locking stick `relay BLAS becomes energized. Relay IEF is reenergized on feed-back code when the train has vacated the stretch. Relay IEFS is then deenergized so that master code is reapplied to the line circuit thus restoring the apparatus to its normal condition.

summarizing the operation o'f Fig. 2, the line circuit ofv this ligure will normally respond to 180 code at all times except when a signal has been cleared for a westbound move or the directional stick relay for the westbound move is energized. In the latter case, the line circuit will be responding to '75 code. When 75 code is effective, the feed-back circuit will energize the locking relay IEF providedthat relays 3WS 'and IWFS are both normal (one energized and the other deenergized) and the stretch of track between the two interlockings is unoccupied. Before an eastbound move can be permitted, 180 code must be received by relay CF at the left-hand end of the line circuit to energize the locking relay IWF and thus permit signal 2R orBR to be cleared for a move past the opposing signal 2L.

Referring now to Fig. 3,v the `vapparatus of this iigure combines certain features "of the apparatus of Figs. l and 2 in order to provide two proceed indications'ior the signals. This-is accomplished by not only polarizing the masterccde in the line circuit but also coding this line circuit at either 75' or 180 code depending upon the traiiic conditions in advance of signal BR. Thus, for trailic from left to right or eastboundthe master code will be of normal relative polarity to permit code following operation of relay CF and energization of locking relay IWF.'V 1f signal 8R isdisplaying a proceed indication, then thelinecircuit will he coded at the 180 vcode rate so that'relayZRD will be 'energized'and will permit the display of a clear proceed indication by

signal

2R or 6R. If signal BR. is'displaying an indication in which the top arm is at stop, relay SRAH which is thevho'me relay for'signal BR Will ne released and the line circuit will be coded at the 75 code rate so that relay' IWF will he energized and relay ZRD will be deenergized to permit the display of anapproach proceed indication by'signal 2R or SR1v The feed back'circuit in Fig. 3 is polarized over the contacts fil and 48 of relay ZLAH which is the home relay for signal 2L. and this circuit controls relays DI and kCFI in a manner similar to that inwhich relays A and CF at the other `end are controlled. :The code operation of relay CFI will cause energizaticn of relay IEFH provided that relay ZLAl-l is deenergized so that relay DI has its contacts closed in the reverse position, as shown. If, on the other hand, relay ZLAH is energized, the contacts of relay DI will be closed in energized provides control of the clear Vindication of signals 8L and I2L.

4 f amines "jThsfacontrolfrof'ithei'ti-alc'irelay IEFS for-the apparatus of :FisQisshown in Fis. .3a und-fis aelfeexplamtory. 'This control isv similar .toethat slimminzFg. lo except for the additionof contact mi rela-y IEFD. Thev control of the trame relay `WFS at the'otherend issimilarto that shown-.inv Fig. Salandwill bezcleariwithout added explaxmtion. Thus,in Fig. by-combining code 4 andgpolarityfeatures YinI the coded feed-back. line circuit, L selective-controler both; the approach and the clear indication of tl'xeentraneesignal-is mdepossible. y f i l n From the. foregoing descriptiom-it will heapparent that Ihave provided eiective andwsafe control of Vtraido, moving in .either directionfover a stretch of track by meansof a polarized-.coded eedfback line lcircuit which' remains effective,

,whenever the stretch is unoccupied,V for` the `re` yersal of the trainedirection. and which prevents such reversal-.bythe r.provision of trailic locking y.

manufacture-whenever the stretch iseccupied, oranfopposing signal displays aproceed: indication. v 3. 'i E ,Although I have herein-shown and-described onlyiafew forms offrailway.traflc controlling ap' paratusembodying my invention, it is understood that varioushanges and modifications may be madetherein -yvithln the scope .of the :appended cliainfisl without departing .from the `spirit and 1 scope. ofr my. invention.

i Having tthus describedmy invention, whatl claim is:

1. In combination withia stretch of track over which trame Vmay move in either direction, a line Acircuit .extending from one to `therotlier end of.

.sive indication oflsaid eastbound headbiock sig- A nal, means effective when said westbound ,trac

. direction .relayis deenergized and .master code Vis being received at saidother end forftransmitting `iinpulsesoi' feed-back code yfrom, said4 other end. togsaid one end of .the line circuithasecondsig- Anal control rela-yat 'saidone end energized infre-v Sponse to the receipt of said feed-back code at saidfone end for controlling the permissive indi-` .of said .Westbound signal, means `elective when saideastbound trafc direction relay is energizedfor're'versing the polarityofsaid. master deti'i cause release of said first signalkcontrol relay. and prevent .the display of said permissive vindication by said eastbound signal, means eiecvtive when said westbound trailcdirection` relay =is energized vfor discontinuing .saidfeed-back code to thereby release said second signal control relay and 'prevent the display of said permissive indi- I ,cationby said .westbound signal, and means for energizing said eastbound or said WestboundV trafcdirection relay inaccordance withthe traf- Ac directionfto be established.

. 2. In combination with a stretch of; track over' which trafllcfmay moveln either direction, a line circuitextending from one to the other end of said stretch,A a normally deenergized eastbound and a westbound traflic direction control relay for? the respective 2ezidsot .'id stxetchgmcangreif festive-whensgiid eastbound-traine direction relay 'is deenergized for supplying impulses' of a muster code otnormal polsrity'to said line circuit at one end thereoLa-first control rela! at, said other.

end of the stretch energizedln respdmeto-...the receipt of, master code oi" only said-normal Dolar- Vity at said other end tor controlling the entry ofl eastbound ytratlic intosaid stretch, means, ell'ec- Ative when said; westbound .tramo direction. relay is deenergized and master. eodeis beingl received at said other end for 'transmitting` impulses of f feed-back code or given polarity Iromgsaid other end to said one end of the linezcireuiti Aa second `control relay `at said one end enersised in re'A kspouse to the receipt of feed-back code'otonly said. given polarity for controlling the entry of lwestbound trame into said stretch,y inconscifective whensaid eastbound tramo dilectiiiflelay is energized for lreversing theipolarity af 8&1!!`

master code to cause a release of saidrstsignal .control relay andprevent yeastbound trame from entering said stretch,means eillective whmysaid westbound trame dlrectionrelay is energized for discontinuingsaid feed-'back 00de and .releasing saidV second control relay vtoflirevent .westbound ztraflicfromfentering said stretch, and means etfective for energizing said` eastbound or said west- `bound trame directionv relay 'in `accordance with vthe `tijailicdirecttonfto be established. .Y

3. In combination with va stretch of tratzfover which trafllc ymay move in` either direction, kaline circuit extending from one `to.they,o tl'ijrer.endgo! said stretch, a. normallydeenergizedeastbound sindl a westbound tralc direction control greleyior therespective endsof :said stretch, means elicotive when said eastbound trame directionrolayjs deenergized i for supplying impulses. olea `:riester .code of a Vfirst coding met `sind iirieycircuitaii:4

one end thereof, a Vrsi.; control relay at other -Kendofl the stretch energized'when and cnlywhen Vmaster code of'said rst coding rate is received at .said other end, saldnrst relay controlling the entryrof eastbound trame into said stretch,`means .eii'ectiye when saidV eastbound tralllc. direction relay is energizedstar'.supplying impulses. af

vmaster code of a second .coding rateoto said line circuit tocause a' release of `saildrst control relayandprevent eastbound trame i'rom entering v said stretch, meansective .when said westbound '.trafiic direction `relay isl deenergized and master code' of either'said .rst or vsaid second jcodingate is being received-at said other end` yior transmitting impulses .of feed-backoco'de from said other to saidcne 'end otthellnecireuitfa second control `relay `at one end .energized .in response tothe receiptof teed-baokcode of 4either saidrrstor saidqsecondnoding'l). tefor -K controlling theentry of 'Westbound tr 4o' into said stretch, means .efreeiivefwrien said west-` bound tratllcr direction relayfls energized for dlsf `continuing said feed-back y.code to release said secondcontrolirelay `andso Drevent r`westbtuithd traflic fromentering said stretch, andlmelnseiviective for energizing said eastboundor said 'west- Lbound trame direction relay in accordancewith the trame direction to be established."

4. Invcombination with fa stretch of 'tracir over` Vwhich trame may move in either direction; aline `circuit rextending Vfrom one 5to theother end of said stretch, an eastbound. entering signal and an eastbound leaving signal tor .said Vstretch; :a westbound entering signal and a westbound leaving. signal for said stretch, `afnormally decider- .Sized estboimdend a-Westboundtramcuirecow control relay for the respective ends of said stretch, means effective when said eastbound traflic direction relay is deenergized and said eastbound leaving signal is at stop for supplying impulses of a master code of normal relative polarity and a first coding rate to said line circuit at one end thereof, means eifective When said eastbound trafc direction relay is deenergized and said eastbound leaving signal is at clear for supplying impulses of a master code of normal relative polarity and a second coding rate to said line circuit at said one end thereof, a rst control relay at said other end of the stretch energized when and only when master code of said normal polarity is received at said other end, said rst relay controlling the approach indication of said eastbound entering signal, a rSt auxiliary control relay at said other end of the stretch energized When and only when master code of said normal polarity and said second coding rate is received at said other end, said first auxiliary relay controlling the clear indication of said eastbound entering signal, means effective When said eastbound traflic direction relay is energized for reversing the polarity of said master code to thereby cause a release of said rst control relay and of said first auxiliary relay and prevent eastbound trailic from entering said stretch, means effective when said Westbound traic direction relay is deenergized and said westbound leaving signal is at stop for transmitting impulses of a feed-back code of one polarity from said other end to said one end of the line circuit, a second control relay at said one end energized in response to the receipt of feedback code of only said one polarity for controlling the approach indication of said Westbound entering signal, means eifective when said Westbound traffic direction relay is deenergized and said Westbound leaving signal is at approach or clear for transmitting impulses of a feed-back code of the other polarity from said other end to said one end of the line circuit, a second auxiliary control relay at said one end energized in response to the receipt of feed-back code of only said other polarity for controlling the clear indication of said Westbound entering signal, and means effective when said Westbound traiic direction relay is energized for discontinuing said feed-back code to cause a release of` both said second control relay and said second auxiliary relay and so prevent Westbound traffic from entering said stretch.

5. In combination With a stretch of track over which traic may move in either direction, a line circuit extending from one to the other end of said stretch, an eastbound and a Westbound trafc direction control relay for the respective ends of said stretch, means effective when said eastbound traffic direction relay is deenergized for supplying impulses of a master code of givenr character to said line circuit at one end thereof, a first control relay at said other end of the stretch energized in response to the receipt of master code of only said given character at said other end for controlling the entry of eastbound traffic into said stretch, means eifective when said eastbound trac direction relay is energized for altering said given character of the master code in such manner as to cause a release of said first control relay and so prevent eastbound trac from entering said stretch, means effective when said Westbound trafc direction relay is deenergized and master code is being received at said other end for transmitting impulses of feed-back code of given polarity from said other end vto said one end of the line circuit, a second control relay at said one end energized in response to the receipt of feed-back code of only said given polarity for controlling the entry of Westbound trafc into said stretch, and

, means effective when `said Westbound traic direction relay is energized for discontinuing said feed-back code to cause a release of said second control relay and so prevent Westbound trame from entering said stretch.

JAMES J. 'VAN ORN.