US2630523A - Centralized traffic control system of the coded reversible track circuit type - Google Patents

Description

.Mmh 3, 1953 "1 F. CADMAN ETAL 2,630,523

CENTRALIZED TRAFFIC CONTROL SYSTEM OF THE CODED REVERSIBLE TRACK CIRCUIT TYPE Filed July 28, 1949 7 Sheets-Sheet 2 J NJ IN VEN TORS [g 15 [m E Cad/nan and THE/l2 47 TOHZVEY March 3, 1953 1. F. CADMAN ET AL 2,630,523

CENTRALIZED TRAFFIC CONTROL. SYSTEM OF THE CODED REVERSIBLE TRACK CIRCUIT TYPE Filed July 28, 1949 v 7 Sheets-Sheet 3 [y la INVENTORS [Pa Cadmazz (02d MEIR HWOIZNZ'Y' March 3, 1953 I F. CADMAN ET AL 2,630,523

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ha 7 i B y w m ,w m w, a: m wmw March 3, 1953 I. F. CADMAN ETAL 2,630,523

, CENTRALIZED TRAFFIC CONTROL SYSTEM OF THE CODED REVERSIBLE TRACK CIRCUIT TYPE Filed July 28, 1949 7 Sheets-Sheet 6 (faiigzz) INVENTORS [Pa F.

BY (fian (a ['tZLZOI? awa e 'Awomvry Patented Mar. 3, 1953 GENTRALIZED TRAFFIC CONTROL SYSTEM OF THE CODED REVERSIBLE TRACK CIR- CUIT TYPE Ira F. Cadman, Wilkinsburg, and Charles W.

Failor, Forest Hills, Pa., assignors to Westinghouse Air Brake Company, a corporation of Pennsylvania Application July 28, 1949, Serial No. 107,354

15 Claims. 1

Our invention relates to centralized trafiic control systems for single track railroads, of the type employing coded track circuits for the protection of main line train movements. Th principal object of our invention is to provide a system giving an adequate measure of protection with fewer signals than are required by the conventional systems, in order to render the system economically suitable for use on single track railroads of relatively light traffic.

In the centralized traflic control systems now widely used on single track railroads, it is the practice to provide passing tracks at intervals of several miles, with the track switch at each end included in a short detector track section over which train movements are governed by a group of four block signals which are interlocked with the track switch by approach locking relays and are manually controllable in accordance with the positions of switch and signal levers at a central office by a suitable remote control system. This arrangement is shown, for example, in Letters Patent of the United States No. 2,229,249, issued January 21, 1941, to L. V. Lewis, for Remote Control Systems. Continuous track circuits are provided for all main track, for the control of these signals in accordance with trafiic conditions to form a block signaling system in which the blocks for the protection of opposing train movements extend from siding to siding or from one end to the other of the same siding.

In the system of our invention as disclosed herein, the manually controllable block signals are arranged in accordance with a novel plan which difiers from that outlined above in that a detector track section defining the end of a block and three block signals are provided at one end only of each siding (the left-hand or west end of the siding, as disclosed herein), while the fourth signal is located at the opposite end of the siding, its purpose being to govern eastbound train movements out of the side track over the track switch at that end. In accordance with this plan, the blocks correspond in length to two successive blocks of the conventional systems, that is to say, they extend from the signals at one end of a siding to the opposing signals at the corresponding end of the next siding to the right or left, respectively, and train movements into each block are governed not only by the signals at its opposite ends, but also by a signal by which a train is enabled to enter the block at an intermediate point. Hand throw track switches are provided at the ends of the passing tracks and their operation is authorized when an illuminated letter S is displayed by a remotely controlled indicator, one of which is provided 2 for each block signal. The signals are of "the two position color light type and no intermediate signals are used other than a conventional distant signal in approach to each block signal which governs high speed train movements.

The control of the block signals and of the associated S indicators in accordancewith traffic conditions is effected by the provision of separate reversible coded track circuit systems. for the single track stretch and for the main track in the siding area.

The coded track circuit system for the single track stretch is of the normally deenergized type, and is so arranged that it may be set into operation for either direction of trafiic movement, by the transmission of a special actuating code over the track rails from the entrance end, by the operation of the control relay for the signal at that end, and the system returns automatically to its normally deenergized condition when the block is vacated by a train. This system corresponds generally to that disclosed in a prior application for Letters Patent of the United States, Serial No. 19,366, filed April 6, 1948, by C. E. Staples, for Normally Deenergized Coded Track Circuit Signaling Systems, which in turn is an improvement upon the system shown in the Staples United States Reissue Patent No. Re. 22,931, dated November 4, 1937.

The coded track circuit system for the main track stretch in the siding area is of the type in which the track rails are normally energized by steady current to detect when the block is unoccupied.

The energization of this last-mentioned coded track circuit system as required for either direction operation is controlled in a novel manner, which constitutes one of the features of our invention, embodied in the provision of a reversible line circuit system extending the length of the siding over which a traific relay at either end may be controlled from the opposite end, to energize or deenergize the system as required.

Another feature of our invention resides in the provisions hereinafter described by which both I track circuit systems may be energized by the operation of the remotely controlled signal control relay for any of the signals so as to effect the clearing of the corresponding signal. In accordance with this feature of the invention the two track circuit systems are energized at times in tandem by coded current supplied at either end of the block for controlling the signal at the opposite end of the block, or are energized in parallel by coded currents supplied at both ends of the block for controlling the signal. which gives access to the block at an intermediate point.

A further feature of our invention resides in the provision of directionally controlled means for enabling the signal at the east end of the siding to be cleared for an eastbound train as soon as a westbound train has passed its location and vacated the single track portion of the block.

Another feature of our invention resides in the provisions by which the signal located at an intermediate point in the block is fully interlocked with those at the ends of the blocks and by which the latter are interlocked with each other by their control of the track circuit systems, this feature providing adequate time locking protection against the clearing of any one of these signals for a suitable interval following the manual return of a conflicting signal to stop.

Other features and characteristics of the system of our invention will be pointed out in the detailed description which follows.

In the accompanying drawings Figs. 1A to IE, inclusive, when arranged side by side with Fig. 1A at the left, show the track plan and the circuits for one complete set of the wayside apparatus for the centralized trafiic control system of our invention, in which Figs. 1A, 1B and 1C show the apparatus located adjacent the track switch lW at the end of a block, while Figs. 1D, 1E and 1F show the apparatus at the intermediate point at which the track switch SW and signal lRB are located. The apparatus located at the right-hand end of this block is not shown for the reason that this is identical to that shown in Figs. 1A, 1B and 1C and may be represented by these views by placing them at the right of Fig. 1F.

Fig. 2 shows in simplified form the apparatus at the control ofiice for the wayside circuits of Figs. 1A to 1F, together with a miniature track diagram of the tracks of a complete block.

In the description which follows the functions of the various elements of the system will first be defined, the general mode of operation of the system will then be briefly described, and finally, the circuits will be traced in detail in connection with the operations involving the movement of trains through the block.

Similar reference characters refer to similar parts in each of the views, and similar relays at different locations are identified in the drawings by different numerical prefixes which correspond to the number of the switch or signal with which they are associated. It is to be understood that when in the course of the description a relay is identified only by a letter combination such as RI-IS, for example, the description applies to each of the relays ZRHS, :iRI-IS, etc., shown on the drawings.

To simplify the drawings, the local sources of current for energizing the various circuits are not shown. Each such source is identified by its terminal designations, the positive and negative terminals being designated B and N, respectively. Certain of the local sources also have a center or middle terminal C.

The remote control system employed in connection with our invention is substantially similar to that described in the hereinbefore-mentioned Lewis patent, and consideration of its detailed mode of operation is not needed further than to note that it provides a plurality of intermittently available control and indication channels between the ofiice and stations at the ends of the sidings.

For simplicity, the various channels which are established by code action are represented herein by the equivalent direct wire connections.

The apparatus of our invention will be described in connection with the traffic ,block shown in the track diagram of Fig. 2, which has an entering signal 2B, and a leave-siding signal ARE for governing eastbound traffic movements into the block and two opposing entering signals BLA and BLC for governing westbound trafiic movements into the block. It will be understood that the block system includes a plurality of successive blocks each arranged like the one shown. These signals are controlled from three successive field stations of the remote control system, comprising one at the location of switch IW for the control of signal 2R and of the opposing entering signals ZLA and 2LB for the next block at the left, one at the location of switch 3W for the control of signal ARB, and one at the location of switch SW for the control of signals 6LA and ELB and of the entering signal 6R for th next block at the right.

In Fig. 2 there are shown three panels of the ofiice control machine each arranged as in the Lewis patent to include a switch lever SW, a signal lever SG and control code starting button STB and connected over the channel wires la-ta, Ill-11) etc., with the three successive field stations at the locations of switches 1W, 3W and 5W, respectively. As already mentioned, the apparatus at the location of switch 5W is not shown because it is identical with that at switch IW. These circuits function in a manner analogous to the code action described in the Lewis patent, that is to say, in response to the pressing of a starting button STB, impulses are transmitted which cause switch and signal control relays such as the relays WS, LHS, RHS and LSS at a selected station to assume positions determined by the positions of the corresponding switch levers SW and SG at the office. As shown herein the switch and signal control relays are of the polar stick type arranged to operate their contacts to the left when terminal B is applied to the left-hand terminal of the relay winding (or when terminal N is applied to the right-hand terminal) and to operate their contacts to the right when these connections are interchanged, the relay remaining in its last operated position when deenergized.

The indication channels for the control of the lamps of the track diagram are also represented schematically herein by direct wire connections, while those for controlling the lamps which indicate switch and signal conditions are not shown, since their operation is conventional.

It will be apparent that although the system of our invention employs hand throw switches, the manipulation is essentially the same, as far as the operator is concerned, as that of the conventional centralized traffic control system employing power operated switches.

Referring now to the wayside apparatus as shown in Figs. 1A to IF, it will be seen that the detector track section IT and the siding section 3T are each provided with a conventional track circuit having a track battery TB at one end and a track relay TR at the other end, while each remaining section is equipped with a reversible coded track circuit having a polar stick transmitter relay LCTP or RCTP and a code following track relay LTR or RTE. at each end. Relay ZRCTP normally has its contacts in the left-hand position, as shown, so that steady current is supplied from the adjacent track battery ERTB to the rails of section 2-4T. Relays 2LCTP, lLCTP and 4RCTP have their contacts normally in the right-hand position, as shown, in which they connect the associated track relay across the rails of the section.

Each code following track relay LTR or RTR is of the biased polar type so connected as to be responsive to current of the polarity supplied by the track battery RTB or LTB at the opposite end of the section but to be non-responsive to current from the adjacent track battery. Relays 4LTR and QRTR, for example, are non-responsive to current from battery 4LTB or 4RTB. even though the insulated joints between sections 2-4T and ART are broken down.

Figs. 1E, 1F, 1A and 13, arranged in the order given, show the coded track circuit apparatus for the opposite ends of the single track stretch which comprises the major portion of the block. Usually this portion will have a length of from five to ten miles and will include a series of cascade connected track sections comprising cut sections and at least two intermediate signal locations for repeating the track circuit currents and for the control of the distant signals 22 and 24. Consideration of these elements is not needed for an understanding of our invention and to simplify the description it Will be assumed that sections 4RT and 2LT are adjoining portions of the same track section.

The normally deenergized coded track circuit system is set into operation by picking up a traffic relay at the exit end of the block, such as the stick relay 4RCS, Fig. 1F, or 2LCS, Fig. 1A, designated the code sending relay, by the transmission of an actuating code impulse over the rails from the opposite end of the stretch. Each code sending relay, when energized, by closing its front control b, picks up a slow release repeater relay 4RCSP or ZLCSP which controls various circuits as required at the exit end of the block and by closing its front contact connects the Winding of the associated transmitter relay lRCTP or ZLCTP to the contacts of a continuously operating code transmitter 150T or I80CT, of the pendulum type, so that the transmitter relay is operated periodically at the rate of 75 or 180 times per minute to supply coded signaling current of the corresponding code frequency to the rails of the stretch.

In response to the coded signaling current received over the rails of section 4RT or 2LT, the code following track relay 4RTR or 2LTR energizes a slow release track repeater relay lRTFP or ZLTFP which completes a circuit over contact 2) of the track relay for supplying impulses of alternately opposite polarity to the primary winding of a decoding transformer DT, inducing impulses in its secondary winding which are rectified by the track relay contact 0 and supplied to a code detector relay 4BR or ZLI-l, which is of the slow pick-up, slow release type and does not assume its energized position until at least three successive impulses of coded signaling current have been received.

Each cycle of the actuating code by which the system is set into operation comprises an on period of about six seconds duration followed by an off period of equal duration. This code is generated by the cyclic operation of a pair of interconnected slow release actuating code relays ABS? and lRSPA, Fig. 1E, which are set into operation by reversing the signal control relay ZRHS, Fig. 1B, or ARHS, Fig. 1E, or by operation of the similar relays 2LSP and 2LSPA, Fig. 1A, which are set into operation by reversing the signal control relay ZLHS, Fig. 1B. The transmission of the actuating code relays is stopped by the energization of the associated code detector relay dRH or 2LH during an oif period in the actuating code. Normally this occurs during the first off period and the actuating code then consists of but a single pulse of six seconds duration.

The operation of the normally deenergized coded track circuit is discontinued when the stretch is vacated and the signal control relay by which the system was set into operation has been restored to its normal, or left-hand position, by the transmission of a restoring code over the rails of the stretch.

The restoring code is generated by the cyclic operation of a pair of slow release restoring code relays 4BR and ARRP, Fig. IE, or ZLR and 2LRP, Fig. 13. Each cycle of the restoring code comprises a steady on period of six seconds duration followed by a succession of '75 code pulses for six seconds terminating with an off period of six seconds duration. This code is transmitted from the entrance end of the stretch, and the effect of the initial steady current pulse is to override the coded signaling current being received from the opposite direction and to stop its further transmission due to the fact that the operation of the transmitter relay contacts from left to right to initiate an off period in the sig naling code enables the associated track relay to be picked up by current received over the rails, and the latter by opening its contact a, discon nects terminal B from the circuits for operating the transmitter relay from right to left. The succeeding period of '75 code transmission then momentarily picks up the code detector relay LH or RH and thereby releases the energized code sending relay, which prevents re-initiation of the signaling code during the off period of the restoring code and thereby prevents further operation of the restoring code relays.

To prevent improper signal operation by the relay LH or RH under the conditions discussed above, the signal circuits are not governed (iirectly by relay 4LH or ZRH but by a code detector repeating relay 4LHPB or ZRHPB which is controlled by two interposed slow pick-up slow release repeating relays tLHP and ALHPA or ZRHP and ZRHPA, so that it does not pick up until coded signaling current has been received continuously for a period of about 20 seconds.

In addition to the foregoing, the apparatus at each end of the single track stretch includes a stick relay such as relay ZRKS or ALKS and a slow release relay such as relay ZRKR or ELKR. The relays RKR and LKR at the opposite ends of the stretch jointly govern the transmission of indications of block occupancy to. the ofiice over the code indication channels M, the operation being such that when the system is set up for eastbound trafiic, for example, the code sending relay LCSP at the right-hand end of the single track stretch is energized and the associated stick relay LKS is released. Under this condition the relay LKR at the right-hand end of the stretch is released and supplies energy to the indication channel I40, as will be readily apparent from consideration of the circuits for the corresponding relay ZLKR of Fig. 1A, and consequently the block indication relay GLBK, Fig. 2, is picked up to prepare a circuit for lamp t-tBKE. At the left-hand end of the single track stretch. relays dRKS and 4RKR, Fig. 1F, are picked up by the codedetector repeater relay 4RI-IP. The circuit assume for lamp 4-6BKE is completed by relay dRBK when relay dRKR, Fig. 1F, is released due to the occupancy of the stretch. When the system is set up for westbound traffic, relay is released by relay QRCSP to hold relay 'ERBK energized, and relay B-LBK picks up to light lamp A-BBKE when a train enters the stretch.

The coded track circuit system for section 2-4T, shown in Figs. 1C-1D, is arranged to be set into operation by energizing a trafiic relay ZRFS or iLFS over a reversible line circuit which includes the line wires 20 and 2| which extend from one end of the siding to the other. This line circuit is energized at the entrance end of the block by the operation of a traffic locking relay ZRTL governed by the signal control relay ZRHS or by a similar relay 4LTL governed by relay 'dRHS or QRCSP.

The transmitter relays 2RCTP and 4LCTP for section 2-4T, likewise the code following track relays ZRTR, and GLTR. and their slow release repeating relays ZRTFP and dLTFP and the code detector relay QLH all function in the manner described for the similarly designated elements of the system for the single track stretch. The system for section 2-4 however includes two additional decoding relays 2RD and 41D which are controlled through resonant decoding units IBUDU of a well-known type and are selectively responsive to coded signaling currents of the 180 1 code frequency only.

The block indication lamp Z- ZBKE for this section is controlled by the indication relay ELBK controlled over the remote control system channel [21) by a slow release relay iLKR. Normally.

and also when the system is set up for westbound trafiic, if section 2-4T is not occupied, relay iLKR is held energized by relay ALTFP. When eastbound traiiic is set up, if section 24T is not occupied, rela ZRTFP is energized and reverses the polarity of the current supplied to relay ELFS, to hold relay GLKR energized.

The indication lamps ITKE', 3TKE and TKE on the track diagram of Fig. 2 are controlled by the indication relays TK governed over the remote control system channels 19a, b and H50, by their respective track relays.

The coded track circuit system for section 2-4'1 also includes two directional stick relays -4LS and INS, which become energized when a westbound train enters section 2-HT and section lT, respectively.

The local interlocking circuits for the signals are to a large extent conventional. These include normal and reverse switch indication relays NWP and RWP which reflect the position and locked condition of the track switches, and in the case of switch iW, are energized only when the switch control relay IWS occupies a corresponding position, a stick repeater relay IRWPS for relay IRWP, block repeating relays BP-R controlled jointly by the signal control and code detector relays, approach locking stick relays RAS and LAS which are released by the relay BPR when a signal is to be cleared and are picked up only when the signal has been restored to stop by the passage of a train or by the operation of a time element device 2TER, the signal relays 2RAI-I, ZLAH, ZLCH and SRBH for controlling the lamps G and R of the color light signals, and the relays ZRSI-I, ZLSS, ZLCSH and 4RSH for controlling the S indicators associated with the signals.

It is to be understood that in practice the system of our invention will include a number of features which have been omitted in order to simplify the drawings, but which nevertheless determine the form and arrangement of the circuits as shown herein to some extent.

For example, the system is arranged to employ 'a minimum amount 'of energy so that primary batteries can be used in territory remote from commercial power sources and includes the conventional means for lighting the signal lamps automatically upon the approach of trains. It is also the practice to employ light-out relays with windings in series with the signal lamps for governing the transmission of signal indications to the office and for controlling the coded current supplied to the distant signals.

Furthermore the system is so arranged that it is suitable for use with a coded cab signaling system of the type shown for example in Letters Patent of the United States No. 1,986,679, issued January 1, 1935, to L. V. Lewis, for Railway Traffic Controlling Apparatus, in which alternating current in the track rails is interrupted at the rate of 75 or times per minute to govern vehicle carried apparatus for the control of the aspects of a cab signal reflecting trafiic conditions ahead of the vehicle. The code frequencies of the track circuit currents employed in our system are the same as those required for cab signaling purposes under each of the different conditions of operation. It follows that alternating currents to which the vehicle carried receivers are responsive may be superimposed upon the current supplied by the track batteries LTB and RTB and that this current will be properly coded by the operation of the relays LCTP and RCTP, as required for cab signaling purposes. Coded alternating currents may be superimpcsed upon the non-coded main line sections, such as IT, in a conventional manner as will be readily understood.

Finally, the apparatus of our invention is arranged in such a manner that automatic clearing of the signals by the approaching trains may be provided for under emergency conditions when the remote control system is disabled, as disclosed, for example, in a co-pending application for Letters Patent of the United States, Serial No. 41,112, filed July 28, 1948, by Harry C. Van Tassel, for Centralized Trafiic Control Systems.

The system of our invention may also be readily adapted to the control of electric switch locks such as are required in centralized traffic control systems for the protection of outlying track switches leading to industrial sidings or the like, but the circuits have not been shown herein in order to simplify the disclosure. Circuits for this purpose suitable for use in connection with the system of our invention are disclosed in a co-pending application for Letters Patent of the United States, Serial No. 14,244, filed March 11, 1948, by C. W. Failor and C. B. Shields.

The mode of operation of the system of our invention, briefly described, is as follows:

1) To clear signal 2B for an eastbound train movement over the main track:

The operator moves the signal lever ZSG to the right, and presses the remote control system starting button I-ZSTB, thereby operating the signal control relay ZRHS, Fig. 113. to its righthand or reverse position. The traffic locking relay 2RTL, Fig. 1C, is thereby energized over contacts a of relays ZRHS and INWP, contact 01 of relay IRWPS, wire 25, and contact I: of relay 9 ZRFS, and the trailic relay 4LFS, Fig. 1D, is energized in the normal direction, its polar contact 01 remaining open, over back contacts 12 and c of relay ZRTFP, front contacts a and b of relay 2RTL, line wire and 2!, and back contacts I) and c of relay 4LTL, and energizes its repeater relay 4LFSP. Relay ZRTL operates the transmitter relay 2RCTP to the right to disconnect battery ZRTB from the rails of section Z-AT, which releases the track relay 4LTR. and its repeater relay ALTFP, and at the same time, relay 4LFS by closing its front contact 0 in a circuit hereinafter traced in detail causes relay 4LCTP to supply '75 code pulses from battery 4LTB to the rails of this section to operate the track relay ZRTR and pick up relay 2RTFP. The closing of front contact 0 of relay 4LFSP sets the actuating code relays 4RSP and 4RSPA, Fig. 1E, into operation, and these relays, by completing circuits hereinafter traced in detail, cause the transmitter relay 4RCTP to supply an actuating code impulse to the rails at the left-hand end of section dRT, to operate the track relay at the right-hand end of the single track stretch, adjacent signal 6R. This track relay, not shown, corresponds to relay 2LTR at the similar location at the right-hand end of section 2LT, in Fig. 1A, and its operation by the actuating code impulse energizes its repeating relay corresponding to relay ZLTFP and also energizes the code stretch release, but the associated code sending relay is held energized over its stick circuit and causes the associated transmitter relay corresponding to relay ZLCTP to supply '75 code to the rails of the single track stretch at its right-hand end. The transmission of an actuating code impulse by relay 4RCTP thus has the result that the coded track circuit system for the single track stretch including section 4RT is set into operation by the code sending relay corresponding to relay ZLCS, at its right-hand end, and in Fig. 1F, relays GRTFP. IRH, IRI-IPA and 4RHP will pick up, due to the reception of coded signaling current over the rails of section lRT by the track relay 4RTR.

The operation of relays 4RTR and ARTFP prevents the transmission of a second actuating code impulse by relay 4RCTP, and when relay 4RHP picks up, relay dRl-IPA releases, energizing relay 4RI-IPB, Fig. 1E, which by opening its back contact I), prevents further operation of the actuating code relays dRSP and 4RSPA, and by the operation of its contact 0 changes the frequency of the coded signaling current supplied to the rails of section 2-4T by relay ALCTP from '75 to 180 code, with the result that the code detector relay 2RD picks up in Fig, 1C and by closing its contact a, energizes the block repeater relay ZBPR over wire 26 and contacts b of relays INWP and ITP. Since rela ZRHS is now reversed, the opening of back contact b of relay 2BPR opens the stick circuit including wires 2! and 28, for the approach locking relay ERAS, which relay releases and completes at its back contact I) the circuit for the signal relay ZRAH including wire 29 and front contact 12 of the normal indication relay INWP, so that relay ZRAH becomes energized to extinguish the stop indication lamp R and to light the proceed indication lamp G, of signal 2R.

It will be seen that the two coded track circuit systems are now energized in tandem, in accordance with a feature of our invention, as a result of the energization of the line wires 20 and 2|. Our invention also includes means for restoring the coded track circuit system for the rear section to its inactive condition as soon as that section is vacated by a train moving through the block, as hereinafter described. The circuits for the transmitter relay ZLCTP of Fig. 1A. are similar to those for the relay LCTP at the location of signals GLA and GLC in Fig. 2, and it will be seen that relay ZLCTP is controlled over wire 30 and front contacts e of the detector section track relay ITR and the approach locking relay ZLAS- for signals ZLA and 2L0. From Fig. 1D it will be seen that the transmitter relay 4LCTP is controlled over a wire 3|, a front contactw of the normal indication relay 3NWP for switch SW and a front contact e of the approach locking relay 4RAS for signal ARB. The transmitter relay ARCTP, Fig. 1F, is controlled over wire 53 and front contacts 0 of relays 3NWP and lRAS, while the transmitter relay ZRCTP, Fig. 1C, is controlled over wire 13 and front contact 0 of the approach locking relay ZRAS for signal 2RA. It follows that the opposing or conflicting signals are fully interlocked by their control of the coded track circuit systems in accordance with a feature of our invention, as will be pointed out hereinafter in detail.

(2) To authorize an eastbound train to enter the siding over switch lW reversed:

The operator first reverses the switch lever I SW and then moves the signal lever ZSG to the right and presses the starting button l-ZSTB, with the result that relays IWS and ZRHS, Fig. 1B, are both operated to the right. Relay INWP is released by the reversal of relay IWS, and its contact a opens the circuit for relay 2R'IL over wire 25 so that the coded track circuit system is not setinto operation in this case. Relay ZRSH is energized over the reverse contact c of relay ZRHS, the reverse contact b of relay IlWS and wire 32, and completes the circuit for lighting the S indicator along with lamp R of signal 2R. to authorize this train movement.

(3) To clear signal GLA for a westbound train movement over the main track:

The operator moves the signal lever GSG to the left and presses button 5-6STB, thereby operating the corresponding signal control relay to reverse. The signal control relay for signal BLA is not shown, since its operation is similar to that of the corresponding relay ZLHS, Fig. 1B, for signa1 ZLA, and as shown for relay ZLHS, the closing of the reverse contact c of this relay completes a circuit over wire 33 for the actuating code relay ZLSP, Fig. 1A, which energizes its repeater relay ZLSPA, and the closing of the front contacts I) of these relays causes the 3.850 ciated transmitter relay ZLCTP to. supply an actuating code impulse to the rails of section 2LT at its right-hand end. The reversal of the signal control relay for signal BLA thus results in the transmission of an actuating code impulse from the right-hand end of the stretch, the reception of which over the rails of section 4RT operates the track relay 4RTR and thereby causes the energization of its repeater relay IRTFP and of the code sending relay lRCS, Fig. 1F, and its repeater 4RCSP. Relay ARCS prepares a circuit over its front contact 0 for the transmitter relay 4RCTP, but this relay does not begin to supply coded signaling current to the rails of section 4RT until the code detector relay 4LH for section 2.-4T picks up. Relay ARCSP; by closing. its contact (1', energizes the traffic locking relay ALTL, Fig; 1D, over: wirev 34, contact 12 of the normally energized track relay 4LTR, and back contact b of relay lL-FSP, and relay 4'LTL then energizes. the traffic relay ZRFS, Fig. 1C; overthe line wires 20 and 21. Bemy ZRFS by closing its front contact sets the transmitter relay 2RCTP into operation at the 75' code rate to supply coded signaling current to the railsof section 2-4T in place of steady cur rent. The energization of the code detector relay 4LH in, response to the operation of the track relay 4LTR by this current causes relay IRCTP to supply coded signaling current to the rails of section 4RT at the left-hand. end of the single track stretch as soon as the actuating code impulse being supplied from the right-hand end of the single track stretch is terminated. The operation. by this coded current of the track relay at the right-hand end of the stretclhadjacent: signal 6R, serves to prevent further transmission. of actuating code impulses and to. energize the code detector relay LI-l for signal SLA by operations similar to those of Example (1). The two coded track circuit systems are now energized in tandem as in Example (1) but in the opposite direction. Since the local circuits for the signal GLA which is to be cleared and not shown, those for the similarly controlled signal 2LA will. be described. It will be seen from Fig. 1A that the code detector relay 2LH, when energized, picks up the repeating relays ZLHPA and ZLHP, and then relay 'ZLHPA releases to pick up relay ZLI-IPB, front contact a of which completes a circuit over wires 26. and. 3.3 to energize the block. repeating relay ZBPR.

Since relay ZLHS is now reversed, the opening of. back contact a. of relay ZBPR opens the stick circuit including Wires 36 and31' for the approach locking relay ZLAS, the release of which completes a circuit over wire 38 for the signal relay ZLAI-I so that this relay becomes energized to extinguish lamp R and to light lamp G of signal 2LA. (or of signal GLA, in the case of the similar apparatus at the right-hand end of the. block having signal 2R at its left-hand end).

(4) To clear signal GLA for a westbound train andv to authorize that train to enter the siding over switch 3W;

The operator reverses. the switch lever 38W, moves lever GSG to. the left. and. then presses button 5-6STB, with the result that the control relays-for signal 6LA corresponding to ZLSS and ZLHSTOI signal. ZLA are operated to reverse. The v resulting operations. are the same as in Example (3) except that. when the signal relay for signal 6LA which corresponds to relay 2LAH is energized. to light the signal lamp G, lamp S is lighted over the circuit including wire 39 and contact a of the. associated relay corresponding to relay ZLSS- The lightingv of lamps G and S of signal 6LA authorizes the. train to proceed. to. the location of switch 3W and enter. the side track over that switch.

(5); To clear signal. 6L0 for a westbound train. movement over the main track:

The operator reverses the switch lever 5SW, moves lever ESG to the left. and then. presses button 55STB, with the result that the control relays at the. location of signal 6L0. corresponding to. IWS and. ZLHS are operated to reverse. The resultingoperations are the same as. in Example (3) up. to the point where. the block repeating relay BPR. becomes energized. Considering. again. 7

the circuits for signal ZLC which are similar to those for signal 6L0, it will be seen that in this case relay ZBPR does not pick up when relay ZLHPB' becomes energized because its circuit is open at the front contact b of relay INWP, which relay has been released by the reversal of the switch control, relay lWS, but that when the code detector relay 2LH picks up, a circuit. is. completed over wires 41 and. ll] for the signal. relay 2LCSH,nwhich relay picks up and lights the. lamp S below lamp R of signal. 2L0 to authorize the train crew to operateswitch 1W to reverse. When this operation is. completed, the reverse indication relay [,RWP andits repeater IRWPS pick up to complete a circuit for relay ZBPR over back contact. 19- of relay INWP and front contact I) of relay IRWPS, and relay ZBPR then picks up and energizes relay ZLCH over wire 42, to light lamp G of. signal ELC. Relay ZLCEH is released by the opening of. back contact 0 of relay ZLCH. and lamp. S. is extinguished.

The. lighting of lamp. G or the corresponding. signal 6L0, with. lamp S dark, authorizes the train to. proceed over the main track to the location. of signal ZLA.

(6.) To-clear signal ELC for a westbound train and to authorize that train to enter the sidingover switch 3W;

The operator reverses the switch levers 3SW and. 58W, moves lever SSG to the left and presses button S-SSTB with the result that the control relays-at the location: of signal (iLC corresponding to. relays. l-WS, ZLSS and ELI-IS areoperated to reverse. The resulting operations are the same as those considered with reference to signal ZLC in Example 5' except that when relay ZLCI-l picks up tolight the signal lamp G, the lamp S remains lighted, since-relay ZLCSH is now energized over wire- 43 and the reverse contact b of the control relay ZLSS'. The lighting of lamp S along with lampG of signal 6L0 authorizes the westbound train to-p-roceedand to enter the next siding over switch 3W reversed.

(7.) To clear signal ERB to authorize an eastbound train toenter the block over switch SW:

The operator reverses the switch lever SSW, moves the signal lever GSG to the right and presses button 3dSTB, with the result that the control relays 3W8 and l'RHS are operated to reverse.

The trafiic locking relay ALTL, Fig. 1D, picks up over wire 34/ and contact a of relay dRHS to set up the coded track circuit system for section. 2-41 for westbound traflic as in Example (3) above, and the actuating code relays tRSP and llRSPA, Fig. 1E, are set into operation by the closing of the reverse contact 0. of relay ARI-IS to. set up the coded. track circuit system for the single track stretch for eastbound traffic as in Example (1) above. That is, relay ZRCTP is set into.- operation to supply coded current to therails of section 2-4T at its left-hand end to oper-- ate the track relay 4LTR at the location of signal. MR3, and at the opposite end of the single track stretch the transmitter relay corresponding torelay ZLCTP is set into opera-tion to supply coded current to the rails of the stretch, including. section 4RT,. to operate the track relay ARTE. It will be evident that the operation of the track relays 4LTR and. ARTE by coded current indicatesv that the entire block is vacant and that the approach locking relays at the ends of the block. are. energized. Upon this condition both of the code detector relays tLH and lRl-l and the. repeater relays ARHP and QRHPB at the location of switch 3W will become energized to complete a circuit for the block repeating relay 4BPR which may be traced from terminal N through its winding over reverse contact b of relay 3W8 to wire I 9, back contact I) of relay iRCSP, wire 23, front contact I) of relay 4LH, back contact ,1 of relay ILFSP, wire 35, front contact a of relay iRHPB to terminal B at the reverse contact of relay IRHS. Relay IBPR will then become energized to release the approach locking relay RAS and energize the signal relay iRSH to light lamp S of signal IRB, and thereby authorize the train crew to operate switch 3W to reverse. When this operation is completed, the reverse switch indication relay SRWP picks up and energizes the signal relay IRBH to light lamp G and to extinguish lamps R and S of signal 4R3, thereby authorizing the train in section 3T to enter the main track over switch 3W.

Signal IRB may also be cleared when the westbound train discussed in Example 3 or 5 above has passed switch 3W and vacated section ART, due to the provision of the directional stick relay 4L3, Fig. 1D, which relay picks up to close its contact b which bridges the contact of relay GLH in the circuit for relay l-BPR when the westbound train enters section 2-4T, as hereinafter described.

The step by step operation of the system will now be explained, in connection with the movement of trains through the stretch, and those circuits the operation of which is not obvious from the drawings will be traced in detail.

By reference to Figs. 1A, 1B and 1C it will be seen that the apparatus at the location of switch IW constitutes a relay interlocking system in which the signals are governed manually by the remote control system and automatically by traffic conditions as reflected by the code detector relays ELI-I and 2RD and by the track relay I TR or its repeater ITP in a manner which conforms to the accepted practice for systems of this character. Each signal in its stop position governs an approach locking relay 2LAS or ZRAS which must be energized to enable an opposing or conflicting signal to be cleared or to enable the switch control relay IWS to be operated, and must be released to enable the associated signal to be cleared. Relay ZRAS, for example, is normally energized over a stick circuit from terminal N which includes its winding and front contact a, wire 21, back contact 0 of the signal relay ZRAH, wire 28, and extends to terminal B at the contacts 12 of relays ZRHS and ZBPR. Relay ZRAS has a pick-up circuit including back contact a of relay ITR by which the relay is picked up automatically when a train enters the stretch and a second pick-up circuit includin a front contact a of a time element relay ZTER which closes at the end of a predetermined delay period of from two to six minutes, following the manual return of signal 2RA to stop. The circuit for relay ZLAS is similar, except that it includes wire 36, back contacts I) of relays ZLAH, ZLCH and ZLCSI-I and wire 31, and extends to terminal B over the normal contact I) of relay ZLHS or over back contact a of relay ZBPR and the reverse contact 12 of relay ZLHS. The switch control relay IWS is operable only when the signals are at stop, its circuit extending to terminal N over contact f of relay lTP, contact 0 of relay ZLAS, wire 35 and back contacts 19 of relays ZRAH and ZRSH. The circuit for the block repeating relay ZBPR extends from terminaluN 14 through its Winding over contacts I) of relays ITP, INWP and IRWPS to wire 26, from which point one branch extends over back contact cl of relay ZLCSP, Fig. 1A, front contact a of relay ZLHPB to wire 33, to terminal B over the reverse contact c of relay ZLHS and the normal contact 0 of relay ZRHS, and another branch extends from wire 26 over contact a of relay 2RD, Fig. 10, back contact a of relay ZRFS, wire M, normal contact b of relay IWS to terminal B over the reverse contact 0 of relay 2RHS and the normal contact 0 of relay ZLHS. The circuit for the signal relay 2RAH extends from terminal N through its Winding to wire 29 and thence over contacts (1 of relays INS and INWP, contacts I) of relays 2RAS, ZTER, ZLAS, ZBPR and 2RHS to terminal B. The circuits for the signal relays ZLAH'and ZLCH extend over wires 38 and 52 to contacts 0 of relays INWP and IRWPS, respectively, and thence over contacts I) of relays 2LAS, 2IER and ZRAS, contact a of relay ZBPR to terminal B at contact b of relay ZLI-IS. Relays INWP and IRWP are normal and reverse indication relays for switch IW, and are controlled in a conventional manner and indicate the position and locked condition of switch IW and also indicate its correspondence with the position of its control relay IWS. Relay IRWSP is controlled in an obvious manner and serves to prevent a change in the indicated route in the event switch IW has been reversed and is restored to normal before section IT is vacated. Relay IRWPS when energized provides a circuit over its front contact 6 for the transmitter relay ZRCTP which is independent of the track relay I'I'R. This enables signal ARB, BLA or BLB to be cleared even though section ['1' is occupied by a train which is entering or leaving the siding at its left-hand end. Relay INS is a directional stick relay which is picked up over wires 45 and 46 by relay ZLAH and its front contact 0 provides another circuit for the transmitter relay ZRCTP which is independent of the track relay ITR, the purpose of which is to enable signal 4RB, tLA

" or BLB to be cleared when section IT is occupied by a westbound main line train.

It will be readily apparent from Fig. 1B that when a train en ters section IT, relays ITR and ITP release. Contact a of relay ITP completes circuits for energizing the signal control relays ZRHS, ZLI-IS and 2LSS in the normal direction and to energize the track indication relay ITK at the ofiice over channel Illa, to indicate the occupancy of section IT by lighting lamp ITKE in the track diagram. Relay ZBPR and the energized signal relay will release, and the corresponding approach locking relay ZRAS or ZLAS will pick up over contact a or c of relay I TR.

In considering the operation of the coded track circuit systems, it is to be noted that the transmitter relays RCTP and LCTP are of the stick polar type arranged so that their contacts remain in the last operated position when deenergized, and that each such relay is shown deenergized with one terminal of its Winding connected to terminal B or N over its own contact a and the other terminal connected over a circuit network to the same terminal B or N. Each such relay is arranged to operate its contacts to the right or left and to open its own circuit, following the connection of its circuit network to terminal N or B, respectively. Relay ZRCTP, Fig. 1C, for example, is operated to the right over back contact 0 of relay ZRFS when relay ZR'IL picks up, and to the left when relay ZRTL releases. i

Referring now to the operations involved in clearing signal 2R as described in Example (1) above, it has been pointed out that relay ZRCTP assumes its right-hand position when relay ZRTL picks up as the result of the reversal of relay ZRHS, and disconnects battery ZRTB from the rails of section Z-AT, thereby releasing relays ALTR and ILTFP, Fig. 1D. Relay 4LFS is energized by relay ZRTL over wires 25 and 2| and initiates the operation of relay QLCTP to supply coded signaling current of 7 impulses per minute from battery 4L'IB to the rails of section 2-41, by completing a circuit for relay ALCTP over wire 3|, front contact a of relay 3NWP, front contact e of relay ZR-AS, wire 41, back contact d of relay ELS, back contact e of relay 4LFSP, front contact 0 of relay 4LFS, wire 49, to contact a of the code transmitter relay 150T, which when picked. up connects the circuit over wire 50 to terminal B at back contact a of relay ARTR. Relay lLFSP picks up and shifts the portion of the circuit from wires 41 to 49 to include its front contact e, wire 48 and back contact 0 of relay iRl-IPB in place of contact c of relay ALFS. Contact a of the code transmitter CT connects the circuit alternately to terminal B over Wire 50 and back contact a of relay GLTR, or to ter-- minal N. Relay ZRTR responds to the code received over the rails of section 24T and energizes relay ZRTFP, which reverses the polarity of the current supplied over line wires and 2|. Relay iLFS closes its reverse contact (2. com leting a circuit over its contact a to hold relay 4LKR energized after relay lLTFP releases.

As mentioned in connection with Example ('1) above, and as hereinafter described in detail, the code detector relay RH forthe single track stretch. also becomes ener ized. When this occurs, the repeater relay QRHBP picks up and its contact 0 shifts the circuit for relay iLCTP- to include contact a of the code transmitter ISESCT so that 180 code replaces 75 code in the rails of section Z-dT. Relay 2RD picks up in response to the 180 code and causes signal 2R to clear in the manner hereinbefore described.

Relays ERTL, eLFS and @LFSP are held energized when signal 2R is cleared, and following its return to stop, until relay ERAS picks up and section IT is vacated, for the reason that wire is connected to terminal B not only at contact a of relay ZRHS but also at back contacts d of relays ERAS and iTP.

When the eastbound train enters section IT signal ER is put to stop and lamp ITKE' in the operators track diagram becomes lighted as has just been explained, and when the train enters section 2-4T the code operation of relay ZRTR ceases and relay ER'IFP releases. Current of normal. polarity is again supplied to relay 4LFS and its contact d opens, releasing relay 4LKR and energizing relay @LBK, Fig. 2, over channel iii) to light the block indication lamp Z- EBKE;

The release of relay ZRTL when section IT is vacated operates relay ZRCTP to the left, causing steady current to be supplied from battery ZRTB to the rails of section Z- lT behind the train. Relay lLFSP is held energized over back contact of relay lLTFP until section Z- lT is vacated, whereupon relays iLTR and lLTFP pick up during an interval between the code pulses being supplied by relay lLCTP. The operation of relay GLCTP is terminated by the opening of back contact a of relay lLTR, and its further tLFSP when. relay ALIZFP picks up.

Relay ALKR is picked up over contact b of relay GLTFP and releases the indication relay dLBK at the oflice, to extinguish the block indication lamp 2-4BKE.

It will be seen, therefore, that the coded track circuit system for section Z- lT is restored automatically to its normal condition as soon as this section is vacated by an eastbound train. As will hereinafter be pointed out, the two coded track circuit systems are also arranged to be energized in tandem for westbound traiiic and in that case also the rear section is restored to normal as soon as it is vacated, these arrangements constituting one of the features of our invention.

Considering now the coded track circuit system for the single track stretch and its mode of operation as required for the clearing of signal 2R as described above, it has already been pointed out that the actuating code relays iRSP and lRSPA of Fig. 1E are set into operation when relay :lLFSP is picked up by the reversal of the signal control relay ZRHS. The circuit for relay ARSP in this case extends over back contact a of relay GRSPA, back contact 17 of relay iRHPB, wire 5|, front contact 0 of relay QLFSP, wire 52 to terminal B over the normal contact 0 of relay ARI-IS. When relay 4R8? picks up it energizes relay lRSPA and thereby opens its own circuit, so that these relays operate periodically, at a rate of about five times per second, until the circuit for relay RSP is opened by relay ERHPB due to the reception of coded signaling current. When relays iRSP and QRSPA are both picked up, the transmitter relay ARCTP is operated to the left and supplies an actuating code impulse from battery QRTB to the rails of section -RT. The circuit for relay ARCTP in this case extends from its winding over wire 53, iront contacts 0 of relays iRAS and 3NWP, back contact b of relay lRRP, Wire 54, back contact I). of relay lRTFP, wire 55, back contact 0 of relay 4L8, wire 58, back contact c of relay ARCS, wire 5?, front contacts I) of relays lRSPA and iRSP, wire 58, and back contact a of relay iRTR to terminal B. The actuating code relay tRSP releases after six seconds and its contact 19 connects terminal N in place of terminal I) to the circuit for relay GRCTP to operate it to the right to terminate the actuating code impulse. If this impulse results in setting the system into operation as explained below, coded. signaling current will be received over the rails of section ART to pick up relays G'RTR. and. iRTFP and relay RCTP will be maintained in its right-hand position by the connection. over wires 53 and 5t to terminal N at front contact I) of relay lRTFP.

This actuating code impulse sets the system into operation by energizing a code sending relay at thev right-hand end of the single track block extending to the location of signal 6R. The circuits for this relay are not shown because they are similar to those for the code sending relay ZLCS of Fig. 1A. By reference to Fig. 1A it will be seen that when an actuating code impulse, is re ceived over the rails of section 2LT, relays ZLTR and ZLTFP will pick up and then the code sending relay ZLCS will pick up over the circuit including contacts d of relays ZLI-I and ZLTR, wire 59, contact 0 of relay iTP and the normal contact d of relay 2LHS.

When the actuating code impulse is terzninated, relays ZLTR and ZL'ITP release to complete circuits for the transmitter relay ELCTP over Wire 30, front contacts e of relays HR and 2LAS, back contact b of relay ELRP, wire til,

5 back contact I) ofrelay ELTFP, front contact 0 of 17 relay 2LCS, contact 01 of relay ZRAH and over wire 6! or 62 to contact b of the code transmitter 15 CT or I85 CT and thence alternately to terminal B at back contact a of relay 2LTR over wire 63, or to terminal N.

Coded signaling current is thus supplied from battery ZLTB to the rails of section 2LT at the 75 code rate when signal ER is at stop and at the 180 code rate when signal ER is clear. These codes control the distant signal 22 in a conventional manner to cause it to indicate caution or proceed, respectively.

The code detector relay at the left-hand end of each single track stretch such as the relay 4RH, Fig. 1F, is responsive to the code operation of the associated track relay at either of these frequencies, but when cab signaling is used, it is necessary to supply 180 code to the sections in the rear of signal 22 in order to provide a proceed cab signal indication when signal 22 indicates caution or proceed, as will be readily understood.

When relay ZLC S picks up as just described it completes a stick circuit at its contact a by which it is held energized until a restoring code impulse is received over the rails of section 2LT. Relay ZLCS energizes its repeating relay 2LCSP, which releases relay 2LKR and thereby energizes the block indication relay ZLBK, Fig. 2, over channel I la.

At the right-hand end of the block shown in Fig. 2, relay SLBK is energized in this manner to enable lamp l-GBKE to be lighted by the operation of relay lRBK, when the single track stretch is occupied by an eastbound train.

Referring now to Fig. 1F, relay SRTR is operated periodically by the coded signaling current received over the rails of section flRT from the right-hand end of the block, following the termination of the actuating code impulse, and relays QRFTP, lRH, lRI-IPA and ERI-IP pick up over obvious circuits and then relay 4RHPA releases. Relay lRHPB in Fig. 1E picks up over wire 64 and contacts b of relays 4RHPA, lRHP and lRl-I, and relay 4RKS picks up over contacts 01 of relays ARHPA and iRHP, contact 1 of relay lRl-f, contact c of relay GRCSP, wire 65, and back contact a of relay lRR.

When the eastbound train above referred to enters section ART, relay ARTR ceases to operate and relays 4RTFP, lRH, 4RHP and 4RHPB release, but relay GRKS is held energized over its own front contact a and back contact ,1 of relay tRH. Relay iRKR has been placed under the control of relays lRHP and ERHPA by the operation of relay :lRKS and now releases due to the opening of contact of relay 4RHP so that relay lRBK at the office becomes energized over channel l lb to light lamp l-EBKE to indicate the occupancy of the single track stretch.

Assuming now that the eastbound train has entered the detector section at the exit end of the block, the code transmitter ceases to supply coded signaling current to the rails because its circuit which is similar to that of relay ZLCTP, Fig. 1A, will be connected over wire 35 to terminal N at the back contact 8 of the track relay corresponding to relay ITR, which relay will also release its repeater relay corresponding to relay ITP, and the latter will close its back contact a to energize the office indication relay TK over channel lilo to light lamp 5TKE.

When the eastbound train vacates the block, lamp 5TKE is extinguished and the transmitter relay corresponding to relay 2LCTP at the exit end of the block is set into operation at the 75 18 code rate so that, in Fig. 1F, relay ARH becomes re-energized, and closes a circuit for the restoring relay 4BR, Fig. 1E, over wire 65, back contact g of relay lLFSP, wire 61, contact b of relay ARI-IS, wire 68, back contact a of relay 4RCSP and contact 0 of relay 4RH.

Relay 4BR picks up, energizing relay 4RRP and opening the circuit over Wire 65, for relay ARKS, which releases, and energizes relay 4RKR, and relay dRKR then releases the ofiice indication relay 4RBK and lamp 4-6BKE becomes dark.

When relay GRRP picks up, the transmitter relay GRCTP is operated to the left during an off period of the received code, to supply current from battery 4RTB to the rails of section ART. The circuit for relay ARCTP now extends over wire 53, front contacts 0 of relays ARAS and SNWP, front contacts b of relays 4RRP and 4BR, wire 58 and back. contact a of relay 4RTR to terminal B.

Relay GRTR remains released due to the opening of the reverse contact b of relay 4RCTP, so that relays lRTFP, lRH and 4BR release, and relay ARRP is deenergized. The closing of the back contact b of relay 4BR causes 75 code pulses to be supplied to relay ARCTP over wire 69, back contact 0 of relay ALI-I, wire ll), front contact a, of relay lRRP and contact b of the code transmitter relay TSCT, causing relay 4RCTP to supply 75 code to the rails of section 4RT for the duration of the release period of relay dRRP. When relay 4RRP releases, relay 4RCTP is operated to the right over the circuit including wires 53, 54, 55, 56 and 5'! and extending to terminal N at back contact b of relay tRSPA.

Assuming that this restoring code, comprising a period of steady energy followed by a series of '75 code impulses, is received at the right-hand end of the block by the apparatus of Fig. 1A, it will be seen that the steady current received during an off interval in the code being supplied by relay ZLCTP Will pick up relay ZLTR to disconnect terminal B from the circuit for relay IZLCTP, and relay ZLTFP picks up to connect terminal N to relay ZLCTP over wires 30 and 6i} and front contact b of relay ZLTFP, holding relay ELCTP in its right-hand position and enabling relay ZLTR to respond to the '75 code portion of the restoring code so that relay 2LI-I will pick up and release the code sending relay 2LCS. Relay 2LCSP releases after a delay period following the release of relay 2LCS and re-energizes relay ZLKR, thereby releasing the block indication re lay 2LBK.

Relay ELBK is released in this manner to open its contact 0 in the circuit for lamp 4-5BKE.

Relay ZLTFP releases when the code operation of relay ZLTR ceases, and the circuit for relay ZLCTP then extends over wires 39 and 60 to terminal N at back contact b of relay ZLSPA. This completes the restoration of the coded track circuit system for the single track stretch to the normally deenergized condition as shown in the drawings.

Referring now to the operations involved in the clearing of signal 2LA or ZLC, corresponding to those for clearing signal BLA or 6L0 for a Westbound train as discussed in Examples (3) to (6) above, it will be seen from Figs. 1A and 13 that in each case, the reversal of relay ZLHS supplies energy over its reverse contact 0, wire 33 and back contact a of relay ZLHPB to set the actuating code relays ZLSP and ZLSPA into operation, and relay 2LCTP is operated to the left to supply 19 an actuating code impulse from battery ZLTB to the rails of section 2LT, over the circuit including its winding, wire Bil, front contacts e of relays iTR and ZLAS, back contact I) of relay SZLRP, wire 59, back contact 2) of relay ZLTFP, back contact c of relay ZLCS, front contacts I) of the actuating code relays ZLSP and ZLSPA and extending to terminal B at back contact a of relay ZLTR. These actuating code relays function in a manner similar to that already described in connection with relays QRSP and iRSPA.

Assuming that this actuating impulse is re- I ceived over the rails of section ART, Fig. 1F, re-

lays ERTR and @RTFP will pick up to energize the code sending relay EROS over the circuit including contacts (1 of relays iRI-I and SRTR, wire contact d of relay lRHS, Fig. 1E, wire it and back contact at of relay lLFSP, Fig. 1D, and relay tRCS will pick up to complete the stick circuit including its own. contact a, wire l2 and contact (1 of relay ELFSP. Relay lRCTP is not set into operation at this time, but its circuit is extended over wire 53, front contacts of relays lRAS and SNWP, back contact b of relay z-RRP, wire Q,

back contact 1) of relay lRTFP, wire 55, back conincluding back contact I) of relay iLFSP, front contact d of relay iLTR, wire 3% and contact at of relay lRCSP. By closing its contacts (1 and a, relay iLTL prepares stick circuits by which it is held energized by relay lRCSP until section 2-41 is occupied and by relay lLTFP until section 2 3T is vacated.

Relay ALTL energizes the traffic relay ilRFS over the line wires and and thereby sets the transmitter relay ZRCTP into operation by completing a circuit which may be traced from its winding over front contact c of relay ZRFS, wire "53, back contact e of relay ERWPS, back contact c of relay iNS, front contact 1 of relay lTR, front contact 0 of relay ERAS, wire it, contact at of relay ZLAI-I, wire 75 or '56, contact a of the code transmitter 750T or ifiilCT and thence alternately over wire ll to terminal B at back contact a of relay ZRTR or to terminal N.

Relay ZRCTP therefore supplies 75 or 180 code to the rails of section 2-iT in place of the steady current which it normally supplies thereto, and in response to the code, relay SLTR energizes relays iLl-l and BLHP, and when signal ZLA indicates proceed, also energizes relay :i-LD.

The circuit for relay dRCTP now extends over wires 53, t l 55 and 55 to front contact 0 of relay :iRCS, as traced above, and thence over wire 69, front contact 0 of relay QLH, contact a, of relay dL-D, wire it or E9 to contact I) of the code transmitter lECT or ldtCT and alternately over wire to terminal 28 or to terminal N. It follows that the '75 or 180 code impulsesreceived over the rails of section Z-d'l are repeated over the rails of section lRT to cause the distant signal 24- to indicate caution or proceed and to energize the code detector relay correspondin to relay 2Ll-I, for signals @LA and ELB at the entrance of section 210 end of the block, enabling iiLA or GLB to be cleared in the manner already described for signals ELA and ZLC.

Referring again to Fig. 1A, it will be seen that when the code detector relay ZLH picks up, the repeating relays ZLHPA and ZLI-IP pick up, and then relay ZLI-IPA releases and relay ELI-IPB picks up and closes at its front contact I) a circuit for relay ZLKS over back contact b of relay 2LCSP, wire 80, and back contact a of relay ZLR. Relay ZLKS picks up and prepares a stick circuit at its contact a over which it is held energized following the release of relay ZLHPB, and its contact b transfers the control of relay 2LKR from contact 0 of relay ZLCSP to contacts 0 of relays ZLI-IP and ELI-IPA.

Assuming now that a westbound train governed by signal EiLA or BLB enters the block, the signal will be restored to stop when the train enters the detector track section including switch 5W, the signal control relays will be restored to normal, and the approach locking relay LAS will be re-energized in a manner similar to that described above in connection with the occupancy IT by an eastbound train. Lamp LGBKE will become lighted, due to the operation of relay tLBK over channel E40 following the release of an indicating relay similar to ZLKR.

In the event the westbound train enters the siding over switch 3W as in Examples (4) and (6) above, section 2- -lT remains unoccupied and when the train vacates section ART and relay 3NWP becomes energized due to the restoration of switch 3W to its normal position, the transmitter relay lRCTP will again repeat the coded signaling current received from section ll-4T into the rails of section dRT.

At the entrance end of the block, as shown in Figs. 1A and 1B, relays ZLTR, ZLTFP and ZLH operate and since relay ZLHS is now in its normal position, the restoring code relay ZLR picks up over the normal contact a of relay ZLHS, contact e of relay iTP, wire M, back contact a of relay ZLCSP and contact c of relay 2LH. Relay ZLR disconnects terminal B from wire and thereby releases relay ZLKS, and relay ZLKR becomes energized and the block indication lamp extinguished to indicate that the single track stretch is no longer occupied.

Relay 2LRP is picked up by relay ZLR and completes a circuit for operating relay ZLCTP to the left during an off period of the code being received, to supply a restoring code impulse of current from battery ZL-TB to the rails of section 2LT. The circuit for relay ZLCTP now extends over wire 30, front contacts e of relays lTR and ELAS, front contacts b of relays 2LRP and 2LR, wire 63 and back contact a of relay ZLTR to terminal B. Relay 2LTR remains released, and relays ZLTFP, ELI-I and ZLR release. The release of relay ZLR deenergizes relay 2LRP, and during its releaseperiod 75 code pulses are supplied to relay ZLCTP over back contact b of relay ELR, wire 8i, back contact (2 of relay ZRAH, and wire 6!, contact lb of the code transmitter relay 'IECT and thence alternately to terminal B over wire 63 or to terminal N. When relay 2LRP releases, relay 2LCTP is held in its right-hand position over the connection to terminal .N over wire (ill, back contact I) of relay ZLTFP, back contact 0 of relay ZLCS and back contact b of relay ZLSPA.

Assuming that this restoring code is received over the rails of section 41311 at the left-hand end of the single track stretch, the steady current portion of the restoring code impulse will pick up relay 4RTR and stop the code operation of relay lRCTP, and relay 4RTFP picks up to hold relay 4RCIP in its right-hand position while relay lRTR is responding to the 75 code portion of the restoring code impulse, by connecting terminal N to wire 54 over its front contact b, to enable relay 4Rl-I to be picked up by the '75 code to release relay lRCS.

When the restoring code impulse terminates, relays 4RTFP and lRH release and relay lRCSP also releases, due to the release of relays GRCS and dRl-I. Relay 4RCTP is connected to terminal N over wires 53, 54, 55, 56 and 51, and back contact b of relay 4RSPA and remains in its righthand position. The coded track circuit system for the single track stretch is now in its normally deenergized condition, as shown in the drawings.

The coded track circuit system for section 2-4'1' continues in operation until relay ARCSP releases. The opening of contact d of that relay disconnects terminal B from wire 34 and releases relay 4LTL, which disconnects terminals B and N from the line wires 20 and 2| causing relay ZRFS to release to hold relay ZRCTP in its lefthand position in which current is supplied steadily to the rails of section 241, as shown.

In the example just described it was assumed that the westbound train left the block via switch 3W and did not occupy section 2-4T. In case the westbound train remains on the main track and occupies section 2-4T as in Example (3) or (5) above, the code operation of relay lLTR ceases when the train enters section 2-41 and relays 4LTFP, 4LKR and 4LH release. Relay 4LI-I deenergizes the slow release repeater relay 4LHP and during its release period the directional stick relay ALS, Fig. 1D, picks up over back contact at of relay ILTFP, front contact a of relay 4LI-IP, wire 82 and front contact 01 of relay 4RCS.

The code operation of relay 4RCTP stopped when relay 4LH released, and its circuit now extends over wires 53, 54 and 55, front contact of relay 4L8, wire 5'! to terminal N at back contact b of relay 4RSPA.

When relay 4L8 picks up, the actuating code relay IRSP is energized over back contact a of relay dRSPA, back contact b of relay dRl-IPB, wire 5|, back contact 6 of relay 4LFSP, front contact e of relay 4LS, back contact a of relay 4LI-IP, wire 82 and contact at of relay ARCS, and relay lRSP energizes relay 4RSPA which extends the circuit for relay lRCTP from wire 51 over front contacts I) of relays ARSP and 4RSPA to terminal B at wire 58, causing relay ARCTP to supply an actuating code to the rails of section IRT.

As soon as the single track stretch is vacated by the westbound train this actuating code will be received at the right-hand end of the stretch With the same result as when supplied for the purpose of setting up the system for eastbound trafiic as already described in connection with Example (1). The code sending relay corresponding to relay ZLCS at the right-hand end of the stretch picks up and causes the associated transmitter relay 2LCTP to supply coded signaling current to the rails at that end, this being the entrance end in the example now being considered. This coded signaling current received from the right over the rails of section dRT during the off period of the actuating code cycle causes relay 4RH to become energized, thereby releasing relay 4RCS and preventing further operation of the actuating code relays IRSP and tRSPA. Relay IRCSP also releases, following the release of relays lRSP and ALI-IPA, and the restoring code relay 4BR is energized over wires 55, 6'1 and 68, by relay 4RH to cause a restoring code impulse to be supplied to the rails of section ART for releasing the code sending relay LCS at the right-hand end of the block and thereby deenergizing the coded track circuit system for the single track stretch in the same manner as when the stretch is vacated by an eastbound train as described above in connection with Example (1).

The block indication lamp I-GBKE becomes dark, since relays 4RBK and GLBK are released during the operations just described, but until section 2- IT is vacated, lamp 2-4BKE remains lighted and relay 4L'IL is held energized following the release of relay iRCTP over its own front contact a and back contact (2 of relay GLTFP.

When the westbound train of Example (3) or (5) passes signal 2LA at the exit end of the block under consideration, the directional stick relay INS is picked up over the circuit including wires 45 and 46 and contact 0 of the signal relay 4LAH, and relay INS is held energized by relay ITP until section IT is vacated.

Relay INS maintains relay ZRCTP in operation while section IT is occupied by the westbound train, its front contact 0 removing contact 1 of relay ITR from the circuit for relay ZRCTP. It follows that as soon as the westbound train vacates section 2-4T, '75 code will again be supplied to relay lLTR, energizing relays 4L'IFP and tLKR, and releasing relays ALTL and 2RFS, and the closing of back contact 0 of relay ZRFS stops the code operation of relay ZRCTP with its contacts in their left-hand position as shown.

It. will be seen from the foregoing that the coded track circuit systems are set up for operation in tandem for westbound trafiic as well as for eastbound traffic, by entrance end control, and that the system for the rear section in each case is restored automatically to normal as soon as it is vacated by the train.

Example ('7) will now be considered in detail, with the assumption that relays 3WS and 4RHS have been reversed by the operator, to clear signal 4R3.

The closing of the reverse contact c of relay GRHS energizes the actuating code relay 4RSP over back contacts a of relays ARSPA and ARHPB to cause an actuating code impulse to be supplied to the rails of section 4RT as in the preceding Examples (1), (3) and (5) to set up the coded track circuit system for the single track stretch as required for eastbound trafiic, relay 4RHPB becoming energized.

The closing of the reverse contact a of relay dRHS energizes relay 4LTL over Wire 34 and sets up the coded track circuit system for section 24 as required for westbound trafiic, as in Examples (3), (4), (5) and (6) already described, relay 4LH becoming energized. If the system for section 2-4T is already set up and is occupied by a westbound train, relay 4LS is picked up and the operation of relay lLI-I is not needed in order to enable signal 4R3 to be cleared.

It will be evident that the time when it is proper to issue the control for signal 4RB to admit an eastbound train to the portion of the block in the rear of a westbound train will be indicated to the operator by the fact that lamp l-BBKE will become dark when the westbound train vacates the single track stretch as exblamed in connection with Examples (3) and (15).. It will also be evident that this information could .not be given if the block indicator remained lighted until the entire block is vacated, as is the conventional practice in centralized trafiiccontrol systems for single trackrailroads.

When relays ARHPB and'ALH are both picked up, indicating that signals 4R, SLA and ESLB are atlstop with their approach locking relays energized and that the block is not occupied, or when dRHPB and lLS are both'picked up, indicating that a westbound train is in the block but'ha's vacated the single track stretch, with signals 6LA and 6LB held at stop, the block repeating relay 4BPR becomes energized .over the reverse contact b of relay 3W8, wire I9, back contact b .of relay 4RCSP, wire 23, contact I) of relay lLs'or contact b of relay lLH and contact 1 of relay 4LFSP, wire .35, front contact a of relay ARHPBand the reverse contact of relay ARI-IS.

Relay GBPR when energized releases the approach locking relay lRAS and energizes relay 'ARSH over back contact a'of relay 3RWP, back contacts b of relays 4RAS and ATER and front contact a of relay ABPR, lighting the lamp S of signal liRB.

This authorizes the operation of switch 3W to reverse by the train crew, and when this operation is completed, relay 3RWP picks up, energizing relay'llRBH in place of relay QRSH, thereby extinguishing lamps S and R and lighting lamp G of signal lRB to authorize the train in section 3T to enter theblock.

When the train enters section iRT, the code w detecting relays ARI-I and ARHP release successively and restore relay ARHS to normal by the momentary closing of a circuit which extends from terminal B through its winding over wire '83 and contacts e of relays 4RI-I and lRHP to terminal N. Relay lBPR is released by relay 4RHPB or IRHS and releases relay 4RBH. Relay 4TER is supplied with energy over back contact atof relay 4RAS, and when energized for a suitable delay period, which may be made relatively short for :the reason that trains in section 3T approaching signal GRB are operated atslow speed, energizes relay QRAS and then releases.

Relay '4LTL is maintained'picked up over back contact j of relay lRAS until that relay becomes energized, and also over back contact '0 of relay 4L'IFP until stretch 2-4T is vacated. When relay GLTL releases, relay 2RFS releases and restores the coded track circuit system for section 2-4'1 to'its normal condition,'as hown, by operating relay 2RCTP to the left to supply steady current to the rails from battery ZRTB.

The coded track circuit system for the single track stretch in this case is restored to normal when the stretch i vacated by the eastbound train as described above in connection with Ex- 2d 1. 'In a centralized tra'flic .control system for railroads for controlling traflic movements into a stretch of track which includes asingle track portion and the main track of .an adjoining double track portion comprising a main track and a side track, three block signals including one at each end of the stretch and one at the junction of said main track and single track portion for governing the movement of traflic into said tretch, a signal control relay for each signal manually controllable from a central oifice, two normally inactivereversible coded track circult systems including one for said main track portion and one for said single track portion, each having .a source of energy and a code :fOllowing track relay t each end with a transmitter relay for alternatively connecting .said source of energy or track relay to the rails of such track portion, each track portion valso having a traffic relay at each end controllable from'its opposite end, and a detector relay controlled by the track relay at each end, .meansfor energizing each detector relay in responseiito the operation of the associated track relay when coded current is received over the rails .of its track portion from the opposite end, means controlled by each traffic relay when energized .for operating the associated transmitter relay periodically to supply coded current to the rails of its track portion, actuating meansiforcontrolling said traiiic .relays rendered effective .by each signal control relay when operated to set the code transmitters at theremote ends of both said track circuit systems into operation to thereby indicate the unoccupied condition of .said'portionsiby the energization of the detector relays t the ends thereof nearest the location of the operated signal control relay in response to currents .supplied to the rails by the transmitter relays at 1 their opposite ends, and meanscontrolled jointly by the operated signal control relay nd the two detector relays governed thereby forclearing the corresponding signal when both such detector relays are energized.

2. In a centralized .trafuc control system arranged as described in claim 1, in which the detector relay for the end of the main track portion adjoining the single track portion controls the adJacent transmitter relay for the single track portion and the detector relay at that location for the end of the single track portion adjoining the main track portion controls the adjacent transmitter relay for the main track portion so that the coded track circuit systems for said two portions are energized intandem when actuated by a signal control relay atthe end of the stretch, said systems beingoperated in-parallel to control said two detector relays at the same location when actuated by the signal control relay at the junction of the-two portions of said stretch.

3. In a centralized trafiic control system arranged as in claim 1 in which means are provided for restoring the operated signal control relay to its normal position when a train governed by the associated signal enters the stretch, and in which restoring means are provided for independently restoring the coded track circuit systems for said main track portion and said single track portion to their normal inactive condition when such portions are unoccupied, as

manifested by the energization of the corresponding detector relays following the return of the operated signal control relay to its normal position, said system including means effective when the route of a train includes both such portions for operating the restoring means for each portion as soon as each portion is vacated by the train, and effective when the route of a train includes only one of said portions for operating the restoring means for both portions when the train vacates such one portion.

4. In a centralized traffic control system arranged as described in claim 1, in which each signal is provided with the usual approach locking relay which is released when the signal is cleared and which picks up at the end of a predetermined time interval when the signal is put to stop manually by the operation of its control relay; manually controllable means for releasing each approach locking relay effective only when the two detector relays which govern the associated signal become energized, and means comprising front contacts of each approach locking relay for preventing the transmitter relay or relays at the same location from supplying coded current to the rails at that location except when such approach locking relay is energized.

5. In a centralized traffic control system arranged as described in claim 4 in which each transmitter relay at an end of the stretch is controlled over a circuit which includes a front contact of the approach locking relay for the adjacent signal for governing the movement of traffic into the stretch, and also includes a back contact of the associated track relay, and in which each transmitter relay at the junction of said portions is controlled over a circuit which includes a front contact of the approach locking relay for the adjacent signal and a back contact of the track relay for the same portion and in addition includes a front contact closed only when the detector relay for the adjacent end of the track circuit system for the other portion of the stretch is energized.

6. In a centralized traffic control system arranged as described in claim l, in which each operated signal control relay is restored to its normal position and the associated approach locking relay reenergized automatically when a train governed by the associated signal occupies the stretch; restoring means for each portion of said stretch, means rendered effective upon the energization of the associated approach locking relay following the return of said operated signal control relay to its normal position for operating the restoring means for each portion provided the stretch is not occupied by a train which is approaching or is in such portion of the stretch, and means controlled by each restoring means when operated for releasing the operated traific relay for such portion to thereby restore the track circuit system for the corresponding portion of the stretch to its inactive condition.

7. In a centralized trafiic control system for railroads for controlling traflic movements into a stretch of track which includes a single track portion with a main track portion and a side track at one end, three block signals for controlling the movement of traffic through said stretch, the first of which is located at one end of the stretch to govern traffic movements through said main track and single track portions, the second is located at the other end of the stretch to govern traffic movements in the opposite direction through said portions, and the third is located at the junction of said portions to govern trafiic movements from the side track through said single track portion only, three manually controllable signal control relays including one at the location of each signal, separate normally inactive reversible track circuit systems for said main track and said single track portions each having at each end a source of energy, a code detector relay, and a transmitter relay for alternatively connecting such track relay or source of energy to the rails of its section, actuating means responsive to the operation of each signal control relay for initiating the periodic operation of the transmitter relays at the remote ends of said track portions, to thereby cause coded energy to be supplied from the respective sources the rails of both track circuit systems to which said detector relays are responsive, the operation of the control relay for the first or second signal being effective to energize such systems in cascade to effect the energization of the detector relay at the location of th operated control relay only when both portions of the stretch are unoccupied, and the operation of the control relay for the third signal being effective to energize such systems in parallel, to effect the energization of the two detector relays at its location only when both portions of the stretch are unoccupied, and means controlled by each operated signal control relay and by the adjacent detector relay or relays, when energized, for clearing the corresponding signal.

8. In a centralized traffic control system arranged as described in claim 7, means for restoring each operated signal control relay to normal when a train governed by the associated signal enters the stretch, restoring means for each reversible track circuit system, effective when operated to deenergize the operated tra'flic relay for such system and thereby restore such system to its normally inactive condition, means rendered eifective following the movement of a train governed by said first or second signal through said stretch for operating the restoring means for said two track circuit systems successively, each when the corresponding track portion is vacated by the train, and means rendered effective when a train governed by said third signal vacates the single track portion for concurrently operating the restoring means for said two track circuit systems;

9. In a centralized traffic control system arranged as described in claim '7, a directional stick relay at the location of said third signal, means for operating said stick relay when a train governed by said second signal enters said main track portion and for releasing such relay when said main track portion is vacated, and means controlled by said stick relay for clearing said third signal in response to the operation of its control relay to permit an opposing train to enter the single track portion in the rear of a receding train in said main track portion, said clearing means being effective when said directional stick relay is energized provided only the adjacent detector relay for the single track stretch becomes energized.

10. In a centralized traffic control system, arranged as described in claim 7, means for restoring each operated signal control relay to normal when a train governed by the associated Sig nal enters the stretch, restoring means for each track portion for restoring the track circuit system for such portion to its normal condition, means for operating the restoring means for the single track portion when a train governed by said second signal vacates said portion provided the control relay for such signal has been. restored to normal, a directional stick relay at the location of said thirdsignal, means for operat

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