US2297121A - Railway signaling system - Google Patents

Description

Sept. 29, 1942. H, s. YOUNG ETAL RAILWAY SIGNALING SYSTEM Filed April 30, 1941 2 Sheets-Sheet l @4 su L WR www mi uw HL u A @l w L Wm Il A@ mw DEP@ WIMN INVENTORS Hmpy oungand 120ml BY i .McCann THEIR ATRNY uw una sept. 29, 1942.

H. S. YOUNG ET AL RAILWAY S IGNALING SYSTEM Filed April 30, 1941 2 Sheets-Sheet 2 INVENTORS H0121@ Szmg 0111130120 AMC'Ca/zm THEIR ATT'oRNEY Patented Sept. 29, 1942 RAILWAY SGNALING SYSTEM Henry S. Young, Wilkinsburg, and Ronald A. Mc-

Cann. Swissvale, Pa., assgnors to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application April 30, 1941, Serial No. 391,104

7 Claims.

Our invention relates to railway signaling systems and particularly to a system for the control of signals on stretches of single track over which traic normally moves in both directions.

In the signaling systems employed ori-stretches of track over which trac moves in both directions it is necessary for a train to control the signals in its rear to warn following trains, and to also control the signals in advance of itself to warn an approaching train of its presence.

The standard practice in absolute permissive block signaling systems is to arrange the equipment so that when a train advances beyond a passing siding, all of the signals in the track stretch between that siding and the adjacent siding in advance and controlling movement of trains in the opposite direction are caused to display their stop indications to thereby prevent a train moving in the opposite direction of trafc from advancing beyond the exit end of the adjacent passing siding.

In addition, it is customary in signaling systems of this type to arrange the signals governing each direction of traino so that when the headblock signal at the exit end of a passing siding is displaying its stop indication, the signal at the entrance end of the siding will display a caution indication, and so that the adjacent signal in the rear thereof will also display a caution indication. This control f the signals is desirable so that when trains moving in opposite directions approach a passing siding at the same time, they will have ample warning of the approach of each other and will be able to stop before colliding even though the passing siding is relatively short.

In the systems heretofore known the signals have operated in the manner outlined above both when the headblock signal at the exit end of a siding is caused to' display its stop indication because a train moving in the direction opposite to that controlled by that signal is approaching the signal, and when the signal is caused t0 display its stop indication because a train moving in the direction of traffic controlled by that signal is immediately in advance of the signal. v

This method of operation of the signals is desirable Where two trains moving in opposite directions are approaching a passing sidingas it provides the relatively long braking distance necing does not require as much braking distance as l is necessary when two trains moving in opposite directions are approaching each other.

If the signals operate as described above when two trains traveling in the same direction are in the vicinity of a passing siding, the second or following train will be given a caution indication sooner than is necessary and the train will unnecessarily reduce its speed. l

It is an object of this invention t0 provide an improved signaling system of the type described which operates so that a train approaching a passing siding will receive a restrictive indication at a point less distant from the rear of a train moving in the same direction than from the front of a train traveling in the opposite direction, to thereby provide ample braking distance for trains moving in opposite directions While not unnecessarily retarding the second or following one of two trains.

A further object of the invention is to provide an improved signaling system of the type described which is arranged so that signals for each direction of traflic are controlled so that when the headblocksignal at the exit end of a passing siding is displaying its stop indication because a train traveling in the opposite direction is approaching the signal, the first and second signals in the rear thereof will display their most restrictive proceed indications, and so that when the headblock signal is displaying its stop indication because a train traveling in the direction of traic controlled by that signal is in advance of the signal, the adjacent signal in the rear will display its most restrictive proceed indication, but the second signal in the rear will display a less restrictive indication.

Another object of the invention is to provide a signaling system of the type described and which is arranged so that a minimum of line wires are required to obtain the desired .control of the signals.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawings.

We shall describe two forms of apparatus embodying our invention, and shallthen point out the novel features thereof in claims.

In the drawings,

Fig. 1 is a diagram of a stretch of railway track equipped with one form of signaling system embodying our invention, and

Fig. 2 is a diagram showing a modified form of system embodying our invention.

Similar reference characters refer to similar parts in each of the two views.

Referring to Fig. 1 of the drawings, there is shown therein a stretch of single track railroad over which traffic moves in both directions. To facilitate description of the equipment it will be assumed that the right-hand end thereof is east and that the left-hand end thereof is west. Accordingly, train movements from left to right are eastbound, and train movements from right to left are westbound.

The track stretch includes passing sidings which are located at appropriate intervals and permit traliic to be diverted from the main track under the customary control of switches. One such passing siding is shown in the drawings. The switch at the left or west end of the siding is designated AW, while the switch at the right or east end of the passing siding is designated BW.

The rails of the track stretch are divided by insulated joints 3 into successive track sections designated IGT, IIT, 12T, etc. Each of these track sections is provided with a track circuit including a track battery connected across the section rails at one end of the section, and a track relay, designated TR with a suitable prex, connected across the section rails at the other end of the section.

Eastbound trafc through the track stretch is governed by a plurality of trackway signals designated'l 2S, 4S, GS, etc., while westbound traffic through the track stretch is governed by a plurality of trackway signals designated IS, 3S, S, etc.

The signals shown in the drawings are of the color light type, but it should be understood that the invention is not limited to the use of signals of this type and that any appropriate form of wayside signals well known in the art may be employed.

Exceptl as hereinafter explained in detail, each of the signals has a green or clear lamp G, a yellow or caution lamp Y, and a red or stop lamp R. The signals at the entrance ends of the passing sidings have upper portions which include the green, yellow and red lamps as illustrated in the drawings, while these signals may also have lower portions, not shown, governing movement of trains from the main track onto the passing siding.

The signals next in the rear of the signals at the entrance endsof the passing sidings include two red lamps and two green lamps as well as a yellow` lamp so as to be capable of displaying a clear signal comprising a green over a red lamp, an approach medium indication comprising a yellow over a green lamp, a caution indication comprising a yellow over a red lamp, and a stop indication comprising a red over a red lamp.

The diagram which forms Fig. 1 of the drawings shows the means for controlling the signals which govern eastbound traffic including the means for controlling the signal 2S. In order to simplify the disclosure the means for controlling the signals` which govern westbound trafc has not been shown, but it should be understood that this equipment is substantially the same as that shown for the eastbound signals.

The means for controlling the signal 2S includes line circuits I, II and III. The line circuit I extends from the signal 2S to a point in advance Of the west end of the passing siding, while the line circuit II extends from the signal 4S at the west end of the passing siding to a point in advance of the east end of the passing siding. The line circuit III extends from the signal SS eastward and is controlled in the manner Well known in the art by traffic conditions in the track stretch between the east end of the passing siding shown and the adjacent passing siding in advance. The supply of energy to the line circuit III may be controlled in the manner shown in United States Patent No. 1,294,736 to Sedgwick N. Wight.

The line circuits I and II are controlled in the manner hereinafter explained in detatil so that at times both direct and alternating current energy is supplied over these circuits.

The track stretch is provided at appropriate locations with sources of direct current the terminals of which are designated B and C, while a source of alternating current having terminals BX and CX is provided.

The equipment is shown in the condition which it assumes when the track stretch is vacant, and when the switches AW and BW are positioned to direct traffic through the main track.

At this time as the track stretch is vacant, energy of normal relative polarity is supplied over the line circuit III to the relay BHD and the neutral contact and polar contact 2| of this relay establish the circuit of the green lamp G of signal GS.

In addition, at this time neutral contact 23 establishes a circuit to supply energy to the pole changing relay SPC and the contacts 25 and 26 of this relay are picked up.

As track section I4T is vacant, the track relay I4TR is picked up and its contact 28 interrupts the circuit of the eastbound directional stick relay SES and thecontacts 30, 3| and 32 of this relay are released. As contact 32 is released, it interrupts connection from the secondary winding of transformer LT to the line circuit 1I and establishes connection from one wire of line circuit II to terminal C of a source of direct current.

At this time the westbound directional stick relay 3WS is released so that connection is established from terminal B of the source of direct current through back contact 34 of relay SWS, front contact 35 of track relay ISTR, and front contact 36 of track relay MTR to the other wire of line circuit II. Accordingly, energy is supplied to line circuit II, and as relay BPC is picked up, this energy is of normal polarity. This energy feeds to the relay 4HD as track relays I3'IR and I2TR are picked up, and as switch controlled contact AWN is closed. 'I'he contact AWN is closed when and only when the switch AW is in its normal position.

As a result of the supply of energy of normal polarity to the relay 4I-ID, neutral contact 38 and polar contact 39 cooperate to establish the circuit of the green lamp G- of signal 4S, while neutral contact 40 partially establishes the pickup circuit of eastbound directional stick relay 4ES. In addition, neutral contact 42 and polar contact 43 of relay 4HD cooperate to establish the circuit of the pole changing relay 4PC, while neutral contact 45 and polar contact 46 cooperate to establish a circuit short circuiting the primary winding of the transformer MT. This prevents inductive discharges of current from the transformer on release of the track relays governing line circuit I and thus reduces arcing at these contacts.

At this time one wire of line circuit I is connected through the secondary winding of transformer MT to terminal C of a source of direct current', While the other Wire of this line circuit is connected through front contact 48 of relay I3TR and front contact 49 of relay I2TR to terminal B of the source of current so that direct current energy is supplied to the line circuit I. As the contacts 50 and 5I of relay 4PC are picked up, the energy supplied to the line circuit I is of normal polarity. This energy feeds to the relay 2HD and the neutral contact 53 and polar contact 54 of this relay cooperate to partially establish the circuit of the upper green lamp G of signals 2S, while neutral contact 55 connects the primary Winding of transformer NT across the wires of line circuit I. This circuit includes a resistor RA in series therewith to limit flow of direct current in the circuit of the transformer primary winding. At this time alternating current is not supplied to the line circuit I so that no energy is supplied through the transformer NT and the associated rectier to the relay 2CD and the contacts of this relay are released. As the contacts 51 and 58 of relay 2CD are released, contact 51 establishes the circuit of the upper green lamp G of signal 2S, while contact 58 establishes the circuit of the lower red lamp R of signal 2S. Accordingly, the signal 2S displays its clear indication which consists of a green over a red lamp.

Operation of equipment on movement of an eastbound train through the track: stretch Release of contact 53 of relay 2HD interrupts the circuit of the upper green lamp G of signal 2S and establishes the circuit of the upper red lamp R so that the signal 2S displays its stop indication consisting of a red over a red lamp.

When the train advances into section IIT, the track relay II'IR releases and additionally interrupts the line circuit I1 while when the train enters section IZT, track relay I2I'R releases and interrupts line circuits I and II. When line circuit II is interrupted, relay 1I-ID is deenergized and its neutral contacts release s o that contact 38 interrupts the circuit of the green lamp G of signal 4S and establishes the circuit of the red lamp of this signal.

In addition, on release of the neutral contacts of relay 4I-ID contact 42 interrupts the circuit of the pole changing relay IPC and the contacts 50 and 5I of this relay release so that on the subsequent supply of energy to the line circuit I the energy supplied to the relay 2HD is of reverse relative polarity.

When the train enters section I2T, track relay I2TR releases and its contact 59 establishes the pick-up circuit of the eastbound directional stick relay 4ES. This circuit includes front contact 40 of relay MHD. However, the track relay IZTR is of a type which is relatively quick to release, while the relay llHD is of a type the neutral contacts of which are slow to release so that the l pick-up circuit of relay #IES is momentarily cornplete. During this-period energy is supplied to the relay 4ES and its contact 62 picks up and establishes a stick circuit including backy contact 59 of track relay IZTR and front contact S2 of relay ISES for the relay winding, while another stick circuit for relay IES is established on release of contact 4U of relay Ill-ID.

OnV picking up of the4 contacts of relay -IIES contact 63 establishes a circuit shunting contact G8 of relay I3TR so that direct current energy is supplied to line circuit I as soon as the eastbound train vacates section I2T.

When the train advances into section IST, track relay ISTR releases and additionally interrupts line circuit II.

When the rear of the train vacates sections IIlT and IIT, the track relays IIITR and IITR pick up, butcontact 49 of track relay IZTR,v continues to interrupt line circuit I. When section IZT is vacated, track relay IZTR picks up and connection is established from terminal B of the source of current through front contact A9 of relay IZTR, and front Contact 63 of relay lES to one wire of line circuit I, While the other wire of this line circuit is connected to terminal C of the source through the secondary winding of transformer MT.

At this time the contacts of relay IPC are re'- leased so that the energy supplied over line circuit I to the relay ZHD is of reverse polarity. On the supply of this energy to the relay ZI-ID its neutral contacts pick up, while its polar contact 54 is shifted to its right-hand or reverse position. As a result of 'picking up of contact 53 and movement of contact 55, the supply of energy to the upper red lamp R of signal 2S is cut off, while the circuit of the upper yellow lamp Y of Signal 2S is established. v The signal, therefore, displays a yellow over a red lamp, which provides the caution indication.

As a result of energization of relay ZHD, contact 55 establishes the circuit' of the transformer NT, but alternating current energy is not suppliedl to the line circuit I at this time so that relay 2CD remains released.

When the train advances into section If'lT,

track relay IQTR' releases and its contact 23 establishes the pick-up circuit of eastbound directional stick relay SES so that the contacts of this relay pick up. Also, upon the release of track relay MTR, its contact 52 opens line circuit III and d'eenergizes relay BHD. The neutral contacts of relay 6R33 are slow releasing so that the pick-up circuit of relay BES will be closed long enough for its front contact 39 to close. Upon the closing of front contact 3B of relay BES, a stick circuit including, back contact 23 of relay MTR is effective and upon the closing of back Contact 69 of relay iii-ID, a second stick circuit is closed which keeps relay EES energized while an eastbound train is in the block of signal 5S.

When the train enters section I5T, track relay IEE'IR releases and additionally interrupts line circuit III.

As a result of picking up of the contacts of relay SES, contact 32 establishes connection from terminal C of the source of direct current through the secondary Winding of transformer LT to one Wire of line circuit II, while Contact 3l partially establishes connection between terminal B and the other wire of line circuit II. This connection does not become complete until the train vacates section IAT and track relay MTR picks up and isY traced from terminal B through back contact 34 of relay SWS, front contact 3l of relay BES, and front contact 36 of track relay MTR.

Accordingly, when section |4T is vacated, direct current is supplied to line circuit II, and this energy is of Ireverse polarity as the relay BPC is released, while alternating current is also supplied to line circuit II as the secondary winding of transformer LT is included in series with the line circuit.

On the supply of direct current of reverse polarity to relay 4HD its neutral contacts pick up, While its polar contacts are shifted from their left-hand or normal positions to their right-hand or reverse positions. At this time the primary winding of transformer MT is connected across` the wires of line circuit II by a circuit which is traced from one line wire through resistor RB, reverse polar contact 45, and front neutral contact 45 of relay 4HD to one terminal of the primary winding of transformer MT, the other terminal of which is connected to the other line wire of line circuit II. Accordingly, alternating current supplied to the line circuit II is supplied through the transformer MT to the line circuit I, while resistor RB substantially prevents flow of -direct current in the transformer primary winding.

When track relay I3TR picks up, its contact 48 is closed to establish connection from terminal B of the source of direct current to one wire of line circuit I after release of contact 63 of relay 4ES. On picking up of contact 40 of relay 4HD the stick circuit of relay 4ES is interrupted and its contacts 62 and 53 release.

At this time contact 43 of relay 4HD is in its reverse position so that energy is not supplied to pole changing relay 4PC even though contact 42 is picked up. Accordingly, the direct current energy supplied to relay ZHD continues to be of reverse relative polarity.

As a result of the supply of alternating current energy to the line circuit I, energy is supplied through the transformer NT and the associated rectifier to the relay'2CD and the contacts of this relay are picked up to thereby maintain the upper yellow lamp lighted while extinguishing the lower red lamp and lighting the lower green lamp. The signal 2S, therefore, displays its approach vmedium indication consisting of a yellow over a green lamp.

At this time as neutral contact 38 of relay 4HD is picked up and polar contact 39 of this relay is in its right-hand or reverse position, the yellow lamp Y of this signal is lighted to provide the caution indication.

It will be seen, therefore, that as soon as th eastbound train vacates section 12T, signal 2S is-conditioned to display its caution indication, and that when the train vacates section WI', signal 4S is conditioned to display its caution indication, while signal 2S is conditioned to display its approach medium indication.

Accordingly, a second or following train will receive an indication of traic conditions in advance from signal 2S, but will not be required to greatly reduce its speed until it reaches signalllS at which point it will receive a caution indication. 'Ihe second or following train, therefore, will not unnecessarily reduce its speed at signal 2S, but will continue until it reaches 4S, while after reaching signal 4S the train will have sufcient distance in which to stop without running into the rear of the preceding train. At this time the braking distance required by the second train is determined only by its own stopping distance since the preceding train is moving in `the same direction, or is standing still, and the two trains are not approaching each other.

When the first train advances beyond signal 8S, this signal is caused to display its stop indication, while energy of reverse relative polarity is supplied by means not shown to the line circuit III so that when the train vacates sections IST and IST, this energy feeds to the relay 61m. As a result, neutral contact 20 and polar 4contact 2| establish the circuit of the yellow or caution lamp Y of signal GS, while contact 23 establishes the circuit of the relay GPC. In addition, contact 60 of relay BHD interrupts the holding circuit of relay BES and the contacts of this relay release.

On release of contact 32 of relay BES one wire of line circuit II is connected directly to terminal C of the source of direct current instead of being connected through the secondary winding of transformer LT. Accordingly, the supply of alternating current to the line circuit II is cut olf, and energy is no longer supplied through the transformer MT to line circuit I and to the relay 2CD so that the contacts of this relay release.

At this time the other wire of line circuit II is connected to terminal B of the source of current through front contact 36 of track relay MTR, front contact 35 of track relay I5TR, and back contact 34 of directional stick relay 3WS so that energy is supplied to line circuit II and to relay 4HD. As the contacts of relay GPC are picked up, the energy supplied to the relay 4HD is of normal relative polarity and polar contact 39 of relay 4HD is shifted from its reverse to its normal position to thereby extinguish the yellow lamp Y and light the green lamp G of signal 4S.

In addition, at this time polar contact 43 of relay 4HD establishes the circuit of the relay 4PC, while polar contact 45 establishes the circuit to short circuit the primary winding of transformer MT. As relay lPC is energized, the energy supplied to relay 2HD is changed from reverse to normal polarity and contact 54 is shifted from its reverse to its normal position, while at this time relay 2CD is released as explained above. Accordingly, the upper green lamp G and the lower red lamp R of signal 2S are lighted so that this signal provides its clear indication.

When the train advances beyond the signal next in advance of signal 8S, the energy supplied to relay GHD is changed from reverse to normal polarity so that contact 2| interrupts the circuit of the yellow lamp Y and establishes the circuit of the green lamp G of signal GS, while contact 23 maintains the circuit of relay SPC so that energy of normal polarity is supplied to line circuit II and signals 4S and 2S continue to display their clear indications.

Operation of system on movement of a westbound train through the track stretch 'When a westbound train leaves the passing siding next in the east of the siding shown, the supply of energy to the line circuit III is cut off in the manner well known in the art.

As a result of deenergization of relay BHD, contact 20 establishes the circuit of the red lamp R of signal SS to prevent an eastbound train proceeding beyond the passing siding. In addition, on release of relay GI-ID Contact 23 interrupts the circuit of the relay BPC so that its contacts release and change the polarity of the energy supplied over line circuit II fronrnormal:

to reverse. On release of.' contact 60pt relay BHD ther pick-up circuit of eastbound directionall stick relay SES is interrupted andy contactsA 3l. and 32 of this relay remain released so that:

alternatingI current energy is notv supplied tcthe line circuit II.

At this time one line Wire of line. circuit II: is connected to terminal B of the sourcethrough` front contact 3% of track relay MTR, front contact 35 of track relay l5TR,.and back contact,

34 of directional relay SWS, While the other line wire of line circuit II is connected through back contact 32 of relayx GES to terminal C.' so. that relay HD is energized and its polar.l con tact Sil-establishes the circuit of the yellow lamp Y of signal iS.

of relay iHD connects the primary winding of transformer MT across the-Wires of line circuit II, but as alternating current is not beingsupplied to line circuit II, no energy is supplied through this transformer to the line circuit I' and relay 2CD remains released. As relay 2CD is released and relay ZHD is supplied with energy of reverse polarity, the upper yellow lamp Y and the lower red lamp R of signal 2S are lighted so that signal 2S pro-vides its caution indication.

It Will be seen, therefore, that when a Westbound train is approaching the passing siding,

signal S displays its stop indication, Whilesig- Ac cordingly, an eastbound train Will begin to renals 4S and 2S display caution indications.

duce its speed when it reaches signal 2S and will have adequate space in which to stop before colliding with the Westbound train, even if the westbound train should continue beyond signal 3S before stopping.

When the westbound train enters section IST, contact 35 of track relay I5TR releases and interrupts line circuit II to thereby cut on the supply of energyto relay :ti-ID.

On interruption of the supply of energy to y,

the relay HD the neutral contacts of this relay release and contact 38 establishes the circuit of the red or stop lamp R of signal 4S. Release of relay fil-ID does-not aiect the supply of energy` to line circuit I and energy of reverse polarity continues to be supplied to the relay ZHD so that the signal 2S continues to display its caution indication.

When the Westbound train under consideration advances into section MT, track relay MTR releases and its contact (i5 establishes the pick-up.

cir-cuit of the Westbound directional stick relay 3WS. This circuit includes front Contact 66 of relay BHD which controls the signal 3S in theV same manner that relay lll-ID controls signal 4S. On the supply of energy to relay SWS itscuit II and to relay HD is additionally inter-Y rupted.

When the westbound train' enters section HiT, contact 28A of relay MTR. is released, but at In addition, polar contact is? interrupts the circuit of relay liPC so that energy. of reverse polarityis supplied over line circuit I torelay ZI-ID. At this time polar contact if this. time theY pick-up circuit of relay SES is interruptedlby contact GOL offrelay SI-IDrsothat' rela-yf GESremains released.

Whenthe Westbound train enters section.l3T, trackV relay ISTR.V releases andl its contactv 48'. interrupts the supply of energy to linecircuit I. so: that relay 2I-ID. releases and contact 53 establishes the circuit of.` the upper'. red lamp Rzof'isignal 2S.` This signal, therefore,.dis1: laysl ared. lamp over a redlarnptoiprovide the stop indication.

If; the westbound train. continues beyond signal. 5S, track relay.` IZTR Willrelease andinf terrupt line circuitLI,` Whilefin similar, mannery track relays HTR and ISTR Will release. when` the train enters; these.- sections. These. track relays, interruptr line circuit I: andthus, cause signal 2S to continuato; display itsestopgindifcation*- From the foregoingitzwill be seen tlfiatvvhen a train traveling in` onedirection advances'beyOIld,l a passing siding, the signals in the rear ofthat' train and controlling train movements in that'` directionare governed in such manner; that the signal at the entrance end of the passing siding Will display its caution indication, While the adjacent signal in the rear thereof will display itsapproach medium indication. rIhis provides a followingV train with a Warning of theV presence of` the rst train without requiring the following. train to reduce its speed before it is necessary to do so.

On the other hand, when a train moving in one direction is approaching the passingsiding, the signals governing movement of trains inthe other direction are controlled in such manner that the signal at the other end of the passing siding` and the signal next in the rear thereof both-display caution indications so that a second train moving in said other direction Will have ample warning ofv the-presence-of the'rst train andV will stop beforerclliding With'that train.

It will be seen also that the control ofA the signals isarranged-in such manner that aminimum'r of' line Wires are required since the approach medium signal indication is provided by superimposing alternating current on the existing line circuits.

Construction of system shown in-Fig; 2

In Fig. 2 of thefdrawingsthere is: shown a modied system for securing the same control of thefsignals as is provided bythe systemshown in Fig. 1.

The system show n inFig. 2is similar tol that shown in Fig. 1, and. diiers therefrom in that coded energy instead of alternating current energy is supplied to the line circuits4 aty times toprovide an additional proceed indication..

The equipmentis shown in Fig. 2 in the-condition which it assumes when the track stretch is Vacant. At this time direct current energy is supplied over line circuit III to relay GHD so that contacts 20 and 2l of this relay establish thecircuit of the green lamp G of signal GS.,

At thistime contact 2.8 of track relay MTR interrupts the circuity of veastbound directional stick relay GES so that contacts` 3l and 32 are released. Contact 32, therefore, interrupts the circuit of code transmitter HCT and this device is deenergized; Contact` 3`I ofrelay ES. establishes connectionirom one Wire of line circuit II` to terminal C of` a.source of direct current, while the other Wire of this line circuit is connected through contact 36 of relay MTR, Contact 35- of relay WTR.,V and contact 34 of relay 3WS to terminal B of the source so that energy is supplied to line circuit II. This energy is of normal relative polarity as the pole changing relay BPC is energized by current supplied over contact 23 of relay ISI-ID.

The energy supplied to the line circuit II feeds tc the relay 4HD and contacts 38 and 39 of this relay cooperate to establish the circuit of the green lamp G of signal 4S, While contacts 42 and 43 cooperate to establish the circuit of the pole changing relay 4PC. As contact 42 of relay 4HD is picked up, the circuit of the primary Winding of decoding transformer IDT is interrupted and the relay 4H is released. In addition, contact 'I0 Vof relay 4HD interrupts the circuit of the relay 4CR, while contact 1I interrupts the circuit of the code transmitter ICT.

At this time one Wire of line circuit I is connected to terminal C of a source of direct current through front contact 5I of relay 4PC and front contact 'I2 of relay 4HD, while the other Wire of line circuit I is connected through front contact 5D of relay 4PC, front contact 'I3 of relay 4HD, front contact 48 of relay I3TR, and front contact 49 of relay IZTR to terminal B of the source. Accordingly, energy is supplied to the line circuit I, and as the contacts of relay 4PC are picked up, this energy is of normal relative polarity and the relay 2HD is energized.

At this time, therefore, contact 'VI of relay 2HD interrupts the circuit of the code following relay 2CR, While contact I8 interrupts the circuit of the primary Winding of decoding transformer 2DT and establishes a circuit to energize a relay 2DP. As relay 2DP is energized, its contact 3i] is picked up and cooperates with the polar contact 54 of relay 2HD and contact 5I of relay 2H to establish the circuit of the upper green lamp G of signal 2S, while contact 58 of relay 2H establishes the circuit of the lower red lamp R of signal 2S.

Operation of system shown in Fig. 2 on movement of an eastbound train through the track stretch When an eastbound train, that is a train moving from left to right, enters section `T, the track relay IDTR releases and interrupts line circuit I so that relay 2HD releases and its contact 'I8 interrupts the circuit of relay 2DP. Accordingly, contact 8E! of relay 2DP releases and establishes the circuit of the upper red lamp R of signal 2S to thereby condition this signal to display its stop indication.

When the train advances into section I IT, the track relay IITR releases and additionally interrupts line circuit I, while when the train enters nects the relay 4CH/across the line circuit II. As line circuit II is interrupted by track relay I2TR, the relay 4CR remains released, While as section IZT, track relay IZTR releases and interrupts line circuit II, and its contact 49 interrupts line circuit I. In addition, contact `59 of relay I2TR establishes the pick-up circuit of eastbound stick relay 4ES so that contact 62 of relay 4ES picks up and establishes a stick circuit for the relay 4ES. The pick-up circuit is interrupted on release of contact 40 of relay 4HD, but release of contact 4t establishes another stick circuit for relay 4ES.

As a result of interruption of line circuit II, relay 4HD releases and its contact 38 establishes thecircuit of the red or stop lamp R of signal 4S. This circuit includes, in addition; back contact 82 of relay 4H. On release of relay 4HD contact 42 interrupts the circuit of relay 4PC and establishes the circuit of the primary winding of the decoding transformer 4D'I, While contact 'I0 conrelay 4PC is released, its contact 59 interrupts the circuit of code transmitter ICT.

The code transmitter ICT has a contact Which when the device is energized is alternately opened and closed at a rate such as to provide a number of energy impulses each minute, such as '75 a minute, Which are separated by periods of equal duration in which no energy is supplied. While the supply of 75 energy impulses a minute is mentioned, this is illustrative only and any desired frequency of energy impulses may be ernployed. 'j'

When the train advances into section I3T, track relay I3TR releases and additionally interrupts line circuits I and II, While when the train enters section I4T, track relay I4TR releases and its contact 28 establishes the pick-up circuit of relay GES so that its contacts 3| and 32 pick up and contact 36 of relay MTR interrupts line circuit II. As a result of picking up of contact 32, the circuit of the code transmitter IICT is established, While contact 3| establishes connection from one line wire of line circuit II through code transmitter contact 'I5 to terminal C of the source. At this time, however, connection from the other Wire of the line circuit to terminal B is interrupted by contact 36 of relay I4TR so that energy is not supplied to the line circuit.

On release of relay MTR its contact 2'8 establishes the pick-up circuit of relay GES and contact 30 of relay SES thereupon picks up and establishes a stick circuit for the relay.

In addition, on release of track relay I4 TR its contact 52 interrupts line circuit III so that relay BHD releases and its contact 60 interrupts the pick-up circuit and establishes the stick circuit for relay 6ES to thereby insure that relay 'SES Will remain energized after contact 28 of relay MTR is picked up.

As a result of release of relay BHD, contact 20 establishes the circuit of the red or stop lamp R of signal GS, while contact 23 releases and interrupts the circuit of the relay SPC.

When the train vacates section I2T, track relay IZTR picks up and establishes a circuit for supplying energy to the line circuit I. At this time one wire of this line circuit is connected through back contact 50 of relay 4PC to terminal C, While the other Wire of the line circuit is connected through back contact 5I of relay 4PC, front contact 63 of relay 4ES, and front contact 49 of relay IZTR to terminal B of the source. Accordingly, energy is supplied to line circuit I, and the connections are arranged so that the energy supplied to the relay 2HD is of reverse polarity. On picking up of relay 2HD a circuit is established to energize the relay 2DP so that its contact 8D picks up, while polar contact 54 is shifted to its reverse position with the result that the upper red lamp R of signal 2S is extinguished and the upper yellow lamp Y is lighted to thereby cause this signal to display its yellow over red or caution indication.

When the train vacates section IST, the track relay ISTR picks up, but line circuit II continues to be incomplete until track relay MTR is picked up. When the train vacates section MTR, connection is established from one Wire of line circuit II through front contact 36 of track relay I4TR, front contact 84 of relay SES, and back contact 34 of relay SWS to terminal B, while the other Wire of the line circuit II is connected agar-rai throughggfront contact S'lofl relay GES and code transmitter contact 'l5 to terminal C so that im'- pulses off' coded energy are' supplied to the line circuit II.

The coded' energy supplied to' line circuit II feedsA t'othe relays GHD and 4CH.;v The relay 4'IlfD'is-of'-` a'f-typev which is relatively slow acting withlthe result that itsneutral contacts remainV released when coded energy is supplied to the relay. The coded energyr supplied to relay ACR produces code following operation of the relay energy is supplied through thev decoding transformer DT to the relay 4H, and contacts 841V andiSEof vthis relay-are picked up so that contact'tflestablishesthe circuit of the relay liPC, while contact 8-2 interrupts the circuit of the red lamp Rand establishes the circuit of the yellow lamp Y- of; signal 4S. Accordingly, the signal 'iS displaysV its caution indication when the train clearssection .l ITIL On the. supply of. energy to relay APC thecontactszofs this relay'pickf up so that the circuit traced above for supplying energy`V to line circuit Itis interrupted, while a circuitin'cluding contact 15? of code transmitter ICT is established to supplyenergy to the line circuit I. This circuit is complete'as'- one. wire of line circuit I is connected through front contact 5e. of relay 41C, back'vc'ontact 13' of relay I-ID, and. code transmit'tercontact 'l'to terminal C, while the other line` wire is.- connected. through. front contact 5i ofrelay lPC; back contact'lZ of relay I-ID, front contact 1.458V of-relay ISTR, and front contact igor relay IZTR to terminal B of the source of current. Accordingly, coded energy is supplied to linecircuit I. The relay ZHD, like the relay I-ID, is immune to coded energy and its contacts becornereleased at this time and establish the circuit of the relay 2CR so that relay ECR, responds to the coded energy supplied to the line circuit and energy is supplied through the decoding transformer 2DT to the relay 2H.

On picking up of the contacts of relay. 2H itsy contact 82 establishes acircuit to energize relay low lamp Y of signal 2S lighted and contact 53 picks up to interrupt the circuit of the lower red lamp and establish the circuit of the lower green i lamp.V Accordingly, when the eastbound train vacates section MT, the signal 2SV displays itsapproach medium instead of its caution indication.

When the eastbound train vacates section SGT,

energy of reverse relative polarity is supplied` over line circuit III to relay @HD andits contact Si) picks up and interrupts the stick circuit of relay SES so that contacts 3l and 32 of this relay release. Release of contact 32 interrupts the circuit of code transmitter IICI, while release of contact 3i interrupts the circuit of the code transmitter contact and connects one wire of the line circuit II to terminal C of the source. At this time the other wire of the line circuit II is connected through contact 33 of relay MTR, Icontact 35 of relay I5TR, and back contact 34 of relay 3WS to terminal B of the source, while contact 23 of relay @HD establishes the circuit of the pole changing relay SPC so that energy of normal relative polarity is now supplied to the line circuit II. In addition, as a result of lenergization of relay, @HD with energy oflreversepolarity, the contacts 2Q and 2i osthisA relay cooperate to establish.V the circuit of the.

yellow lamp Y of signalA G'S so that thissig'nal provides its caution indication'.

On the supply-of? energy ofi normalpolarity to line -circuitI-II the-neutralfcontacts of relay 4HD pick up-- and` contacts 33 and 39 of this relay cooperate tol establish the circuit of the green lamp Ctofsignal 4S, whilec'ontactAZ interrupts the circuiti oi`4v decoding transformer 4D? andl contacts rl'and i3r cooperate to establish a-circuit?. to4 maintainf relay I#PCA energizedi In addition;V4 contact ilinterrupts the stick circuit of the directional. stickl relay QES, while contact 'I I interrupts? the. circuit of the codev transmitter ICT. and' contact. 10; interrupts the: circuit of the relayi'liCR. A'slthe. relay CR no longer follows code,1contact 8l" of relay'dHr'eleases, but energy is supplied to relay 4PC over contacts 42 and 43 of relay tI-IDL On picking up of the contacts of relayv AHD contact 'I3 interrupts the circuit of the*V codetransmitter contact 'l5 and establishes connectionrfrom' onefwire of'line circuit I through contact 48' of track` relay ISTR and' contact #lg-of track: relay I'ZTR to terminal Bi of the sourcel of current; while contact 'I2 connects the other wire of the line circuit to terminal C. Accord'- ingly, steady energy is suppliedl to the line circuit I, while asthe contacts of relay IPC are picked up,V this energy is of normal polarity.

On the supply of this energy to relay ZHD its contacts" pick4 up and interrupt the cir-cuit of therelay 2CR-,while relayZHreleases and polar contact 54 is shifted to its normal position. Accordingly, the circuits'of the upper'yellow and lowergreen lamps are interrupted and the circuits oi the upper green and lower red lampsA are establishedso that signal ZSagain-displays its clear signal.

Operation of systemV shown in. Fig. 2.011, movement ofan` westboundY train through theV track stretch.

Assuming thatthe track-stretch isotherwise gle track stretch at the right of-thepassing siding,.the"supply of energy to the line circuit III is cut oir and relay BHD releases and its'contact 2,0 establishes the circuit ofA the red or stop lamp Rof signal ES, while its contact 23 interrupts the circuit of the pole changing relay SPC so thatthe energyY supplied to line circuit II is changedirom normal to reverse polarity.

On this change in the energy suppliedto relay dI-ID'thepolar contacts of this relay are shifted tortheirI reverse positions and contacts 38 and 39 'establish the circuit of` the yellow lamp Y of signalJiS. In addition, at this time contact 43 interrupts the circuit of the pole changing relay APC and its contacts release andchange the polarityvof: the-energy supplied to line circuit I from` normal yto reverse.

As a result, `the polar contact 5ft` of relay 2HD is shifted to its reverse position to thereby eX- tinguishlthe upper green lamp and light the upper` yellowy lamp Y of signal 2S', while the lower red lamp R of thissignal remains lighted to cause the signal to display its vcaution indication.

`It will be seen, therefore, that when a Westbound `train is approaching the passingsiding, the signal-atthe opposite end of the siding and governing traiiic in the opposite direction, as

well as the adjacent signal inthe rear thereof displaycaution indications. Accordingly, an eastbound train approaching thepassing siding will 4hayetample warningof. the approach of-thewestbound train and will be able to stop beforer colliding with the westbound train.

When the westbound train enters section T, track relay I5TR releases and its Contact 35 interrupts line circuit II so that the supply of energy over line circuit II is cut oft and relay 4HD releases and its contact 38 establishes the circuit of the red or stop lamp R of signal 4S. At this time energy of reverse relative polarity continues to be supplied to line circuit I so that signal 2S continues to display its caution indication.

When the westbound train advances beyond signal 3S, track relay MTR releases and relay 3WS is energized so that its contact 34 prevents the supply of energy to line circuit II. The relay 3WS is controlled in a manner similar to relay 4ES.

When the westbound train advances into section I3T, track relay I3TR releases and its contact 48 interrupts the supply of energy to line circuit I and relay 2IID thereupon releases and interrupts the circuit of relay 2DP so that contact 8U of relay ZDP releases and establishes the circuit of the upper red lamp R of signal 2S to thereby cause this signal to display its stop indication.

It will be seen, therefore, that the system shown in Fig. 2, like that shown in Fig. 1, is arranged so that when two trains traveling in opposite directions are in the vicinity of a passing siding, the signals operate to provide restrictive indications to insure adequate stopping distance for the trains, while when two trains traveling in the same direction are in the vicinity of a passing siding, the signals operate to provide adequate warning of the presence of the first train without unnecessarily requiring the second train to reduce its speed.

Although we have herein shown and described only two forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

l. In combination, a stretch of railroad track over which traffic moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a first signal at the exit end of the siding, a second signal at the entrance end of the siding and a third signal in the rearof said secon-d signal, said rst and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium, a caution and a stop indication, a iirst line circuit substantially coextensive with said Vsiding and governed by traic conditions in the track stretch adjacent said siding, a second line circuit extending between the second and third signals and governed by traic conditions in the track stretch intermediate said signals, means governed by trafc conditions in the track stretch in advance of the rst signal and controlling the supply of energy to the first line circuit, said means being operative when said stretch in advance of the rst signal is vacant to supply energy of a first character to said line circuit, when said stretch in advance of the rst signal is occupied by a train moving in said one direction to supply energy of a second character to said first line, circuit, and

when said stretch in advance of the first signal is occupied by a train moving in the other direction to supply energy of a third character to said first line circuit, electroresponsive means receiving energy over said first line circuit and controlling said second signal and also controlling the supply of energy to said second line circuit, said electroresponsive means being eiective on the supply thereto of energy of said rst character to condition said second signal to display its clear indication and to effect the supply of energy of said rst character to the second line circuit, said means being effective on the supply thereto of energy of said second character to condition said second signal to display its caution indication and to effect the supply of energy of said second character to said second line circuit, and being effective when supplied with energy of said third character to condition said second signal to display its caution indication and to effect the supply of energy of said third character to said second line circuit, said means being eective when deenergized to condition said second signal to display its stop indication and to effect the supply of energy of said third character to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling said third signal so as to cause said signal to display its clear, approach medium or fcaution indications according as energy of the iirst, second or third characters are supplied thereto and when no energy is supplied to said means to cause said signal to display its stop indication.

2. In combination, a stretch of railroad track over which traiiic moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a first signal at the exit end of the siding, a second signal at the entrance end of the siding and a third signa] in the rear of said second signal, said rst and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium,

f a caution and a stop indication, a first line circuit substantially coextensive with said siding and governed by traflic conditions in the track stretch adjacent said siding, a second line circuit extending between the second and third signals and governed by traiic conditions in the track stretch intermediate said signals, means governed by traic conditions in the track stretch in advance of the first signal and controlling the supply of energy to the first line circuit, said means being operative when said stretch in advance of said first signal is vacant to supply direct current of normal polarity to said rst line circuit and being operative when said stretch in advance of said rst signal is occupied to supply direct current of reverse polarity to said first line circuit, said means being operative when the train occupying said stretch in advance of said rst signal is moving in said one direction to also supply alternating current energy to said rst line circuit, electrore'sponsive means receiving energy over said first line circuit and controlling said second signal and also controlling the supply of energy to said second line circuit, said electroresponsive means being effective on the supply thereto of direct current of norma1 polarity to condition said second signal to display its clear indication and to effect the supply of direct current of normal polarity to the second line circuit,

said means being effective on the supply thereto of direct current of reverse polarity to'conditi'on said second signal to display its caution indication and to effect the supply of direct current of reverse polarity to said second line circuit,V said means being effective when supplied with alternating current to effect the supply of alternating current to said second line circuit, said means being effective when' deenergized to condition said second signal .to display its stop indication and to effect the supply of direct current of reverse polarity to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling saidthird signal so as to cause said signal to display its clear, approach medium or caution indications according as direct current of normal polarity, direct current of reverse polarity together with alternating current or direct current of reverse polarity alone is supplied thereto, and when no energy is supplied to said means to cause said third signal to display its stop indication.

3. In combination, a stretch of railroad track over which traffic moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a rst signal at the exit end of the siding, a second signal at the entrance end of the siding and a third signal in the rear of said second signal, said first and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium, a caution and a stop indication, a first line circuit substantially coextensive With said siding and governed by trafc conditions in the track stretch adjacent said siding, a second line circuit extending between the second and third signals and governed by traic conditions in the track stretch intermediate said signals, means 4governed by traffic conditions in the track stretch in advance of the rst signal and controlling the supply of energy to the first line circuit,said means being effective when said stretch in advance of said vfirst signal is vacant to supply direct current of normal polarity to said `first line circuit and being effective when said stretch in adva-nceof the first-signal is occupied to supply direct current of reverse polarity to said first line circuit, a directional stick relay, means effective when a train moving in said one direction 'enters said track stretch in advance of said first signal to energize said directional stick relay, said relay being effective When energized to supply alterl nating current energy to said first line circuit, electroresponsive means receiving energy over said first line circuit and controlling said second signal and also controlling the supply of energy to said second line circuit, said electroresponsive means being effective when supplied with direct current of normal polarity to condition said second signal to display its clear indication and to effect the supply of direct current of normal polarity to said second line circuit, saidV means being effective when supplied With direct current of reverse polarity to condition said second signal to display its caution indication and to supply direct current of reverse polarity to said second line circuit, said means being also eiective when supplied with alternating current to effect the supply of alternating current to said second line circuit, said means being effective when deenergized to condition said second signal to display its stop indication and to supply direct current of reverse polarity to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controllingsaid third signal so as to cause said signal to display its clear, approach medium or caution indications according as direct current of normal polarity, direct current of reverse polarity together with alternating current or direct current of reverse polarity alone is supplied thereto, and when no energy is supplied to said means to cause said third signal to display its stop indication.

4. In combination, a stretch of railroad track over which traffic moves in both directions, said track stretch including a passing siding, a plurality of ignals governing movement of trains in one direction through said track stretch, saidl signals including a first signal at the exit end of the siding, a second signal at the entrance end of the siding and a third signal in the rear of said second signal, said-first and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium, a caution and a stop indication, a first line circuit substantially coextensive with said siding and governed by traffic conditions in the track stretch adjacent said siding, a second line circuit eX- tending between the second and third signals and governed .by traffic conditions in the track stretch intermediate said signals, means governed by traffic conditions in the track stretch in advance of the first signal and controlling the supply of energy to the first line circuit, said means being effective when said stretch in advance of said first signal is vacant to supply direct current of normal polarity to said rst line circuit and being effective when said stretch in advance of the first signal is occupied to supply direct current of reverse polarity to said rst line circuit, a directional stick relay, means effective when a train moving in said one direction enters said track stretch in advance of said rst signal to energize said directional stick relay, said relay being effective when energized tol supply alternating current to said first line circuit, a line relay receiving energy over said rst line circuit and effective when supplied with direct current of normal polarity to condition said second signal to display its clear indication and to supply direct current of normal polarity to said second line circuit, and When supplied with direct current of reverse polarity to condition said second signal to display its caution indication and to supply direct current of reverse polarity to said second line circuit, said relay being also effective when deenergized to supply direct current of reverse polarity to said second line circuit, a transformer having its primary Winding connected to receive energy from said first line circuit and its 4secondary winding connected to supply energy to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling said third signal so as to cause said signal to display its clear, approach medium, caution or stop indications according as direct current of normal polarity, direct current of reverse polarity together with alternating current, direct current of reverse polarity or no energy is supplied to said means.

5. In combination, a stretch of railroad track over which traffic moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a first signal atthe exit -end of the siding, a second signal -at the entrance end of the siding and a third signal in the rear of said second signal, said rst and second signals being capable of displaying-a clear, a caution and a stop indication; said third signal being capable of displaying a clear, an approach me-V dium, a caution and a stop indication, a first line circuitI substantially coextensive with said siding and governed by traiic conditions in the track stretch adjacent said siding, a second line circuit extending between the second and third signals and governed by traiiic conditions in the track stretch intermediate said signals, means governed by trailic conditions in the track stretch in advance of the rst signal and controlling the supply of energy to the rst line circuit, said means being effective when said track stretch in advance of said rst signal is vacant to supply direct current of normal polarity to said rst line circuit and being eiective when said stretch in advance of said rst signal is occupied to supply direct current of reverse polarity to said rst line circuit, said means being effective when the train occupying said stretch in advance of said rst signal is moving in said one direction to alternately interrupt and establish the supply ofv energy to said iirst line circuit to thereby cause the energy supplied thereto to be coded, electroresponsive means receiving energy over said first line circuit and controlling said second signal and also controlling the supply of energy to said second line circuit, said means being effective when supplied with steady current of normal polarity to condition said second signal to display its clear indication and to supply direct current of normal polarity to said second line circuit, said means being effective when supplied With steady direct current of reverse polarity to condition said second signal to display its caution indication and to supply steady direct current of reverse polarity to said second line circuit, said means being effective when supplied with coded direct current to also condition said second signal to display its caution indication and to supply coded direct current to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling said third signal so as to cause said signal to display its clear, approach medium, caution or stop indications according as steady direct current of normal polarity, coded direct current, steady direct current of reverse polarity, or no energy is supplied to said means.

`6. In combination, a stretch of railroad track over which traffic moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a first signal at the exit end ot the siding, a second signal at the entrance end 'of the siding and a third signal in the rear of said second signal, said first and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium, a caution and a stop indication, a rst line circuit substantially coeXtensive with said siding and governed by traiiic conditions in the track stretch adjacent said siding, a second'line circuit extending between the second and third signals and governed by traffic'conditions in the track stretch intermediate said signals, means governed by traffic conditions in the track stretch in advance of the first signal and controlling the supply of energy to the lfirst line circuit, said means being effective when saidV stretch in advance of said rst signal is vacant to supply steady direct current of normal polarity to said rst line circuit and being effective when said Stretch in advance of said i'lrst signal is occupied to supply direct current of reverse polarity to said rst line circuit, a directional stick relay, means eiective when a train moving in said one direction enters said track stretch in advance of said first signal to energize said directional stick relay, said relay being operative When energized to include a contact of a coding device in the circuit for supplying coded energy to said rst line circuit, electroresponsive means receiving energy over said first line circuit and controlling said second signal and also controlling the supply of energy to said second line circuit, said electroresponsive means being effective when supplied with steady energy of normal polarity to condition said signal to display its clear indication and to supply steady energy of normal polarity to said second line circuit, said means being eiective when supplied with coded energy to condition said signal to display its caution indication and to supply coded direct current to said second line circuit, said means being effective when supplied with steady. direct current of reverse polarity to condition said second signal to display its caution indication and tosupply steady direct current of reverse polarity to said second line circuit, said means being effective when deenergized to condition said second signal to display its stop indication and to supply steady direct current of reverse polarity to said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling said third signal so as to cause said signal to display its clear, approach medium, caution or stop indications according as steady direct current of normal polarity, coded direct current, steady direct current of reverse polarity or no energy is supplied thereto.

' 7. In combination, a stretch of railroad track over which trafc moves in both directions, said track stretch including a passing siding, a plurality of signals governing movement of trains in one direction through said track stretch, said signals including a rst signal at the exit end of the siding, a second signal at the entrance end of the siding and a third signal in the rear of said second signal, said first and second signals being capable of displaying a clear, a caution and a stop indication, said third signal being capable of displaying a clear, an approach medium, a caution and a stop indication, a rst line circuit substantially coextensive with said siding and governed by traiiic conditions in the track stretch adjacent said siding, a second line circuit extending between the second and third signals and governed by traific conditions in the track stretch intermediate said signals, a directional stick relay, means effective when a train moving in said one direction enters said track stretch in advance of said first signal t0` energize said directional stick relay, means governed by said directional stick relay and by traiiic conditions in said track stretch in advance of said first signal for supplying energy to said first line circuit, said means being effective when said stretch in advance of said first signal is vacant to supply energy of a rst character to said rst line circuit, when said stretch in advance of said first signal is occupied by a train moving in said one direction to supply energy of a second character first character to condition said secon-d signal to l0 display its clear indication and to supply energy of the rst character to said second line circuit, when supplied With energy of said second character to condition said second signal to display its caution indication and to supply energy of said 15 second character to said second line circuit, when supplied with energy of said third character to condition said second signal to display its caution indication and to supply energy of said third character to said second line circuit, and when not supplied with energy to condition said second signal to display its stop indication and to supply energy of said third character to the said second line circuit, and electroresponsive means receiving energy over said second line circuit and controlling said third signal so as to cause said signal to display its clear, approach medium, caution or stop indications according as energy of the first, second or third characters or no energy is supplied thereto.

HENRY S. YOUNG. RONALD A. McCANN.

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