880,634. C.T.C. systems. GENERAL RAILWAY SIGNAL CO. April 3, 1959 [April 24, 1958], No. 11387/59. Class 105. In a central traffic control system for controlling the movements of railway traffic over a stretch of track. which is divided into zones by visible and inductive markers, the central office controls directly the signalling equipment on each train passing over the stretch by radio communication. In addition to the signalling equipment, each train carries zone control equipment which detects its entry into and exit from each zone and transmits this information and an identifying signal to the central office, appar. atus for receiving and storing the transmitted central office signals and apparatus for automatically applying the train brakes under certain conditions. Track layout.-Figs. 1A and 2A indicate a track layout comprising a single track with passing sidings divided into zones by the markers 10.2, 12.1, 12.2, &c. Even numbered markers co-operate with east bound traffic and odd numbered markers with west bound traffic, the zones are numbered according to the preceding marker providing individually defined zones for each direction of traffic. The markers are either " permissive " or " absolute " (marked A) beyond which no train shall proceed without a proper cab signal. Each marker, e.g. 14.1 comprises in the direction of movement of the train (west) with which it co-operates, a set of annunciator coils which in co-operation with check in apparatus on the train produces an audible " approach to marker " signal in the train cab, a train stop inductor which cooperates with the train carried automatic stop equipment, check-in coils 14.1 which in cooperation with check-in apparatus in the front of the train initiates a signal to the central office indicating a train entering zone 14.1 and check-out coils 14.1 which in co-operation with check-out, apparatus at the rear of the train initiate a signal to the central office indicating that the train has left the preceding zone 16.1. Each marker is identified by turning its checkin and check-out coils to a particular combination of frequencies, e.g. marker 14.1 tuned to frequencies B and C, marker 16.1 to frequencies A and B &c., all annunciator coils are tuned to frequencies A and D. The trackside coils are inert and unconnected to the control office. Train carried apparatus.-In the front of the train, Fig. 2B, e.g. train 1 travelling east, the check-in transceiver comprises a transmitter sweeping a band of frequencies to which the check-in and annunciator coils are tuned. In passing the check-in coils (14.2) signals are transmitted between the transmit and receive coils PC of the transceiver at frequencies A and B and operate relays in the output circuits of two or a series of tuned amplifiers tuned to frequencies A, B, C, &c. This results in the energizing of a location tone relay which selects a particular tone for modulating the train transmitter. A second tone is chosen by a train identification selector switch which is positioned before entry into the controlled zone. When the location tone relay is picked up a first keying relay drops away opening the circuit of a second slow-acting keying relay, the transmitter which is energized via a back contact of the first relay and a front contact of the second operates during the release time of the slow-acting relay and transmits to the control office a carrier frequency F1 modulated by the location tone and the identification tone. A monitor receiver on the train prevents transmission when another train in the controlled stretch of track is transmitting check-in intelligence. In a similar manner the train carried check-out transceiver and transmitter signal the train identification and location information to the control office at a carrier frequency of F2. Control office equipment, Figs. 1A and 1B. At the output of the control office check-in receiver (F1) the location tone activates one of a group of selective amplifiers and operates a relay in its output circuit. The identification tone activates a tuned amplifier allocated to that train, the energizing of the relay and activation of the amplifier operate one of a series of checks in relays which indicates that a particular train has checked into a particular zone. Via the check-out receiver (F2) one. of a series of check-out relays is similarly operated indicating a particular train leaving a particular zone. A check-in and check-out unit, Fig. 3C (not shown), is provided for each zone comprising a P1 relay for each train checking into the zone and a P2 relay for each train checking out of the zone. The proper operation of these relays is checked by a P3 series of relays. A normally operated TRX relay is released when a train is present in the zone and a CH relay is provided to start the transmission of a control office signal. The office is provided with a control panel including a zone diagram and signal-operating levers. The zones are selectively illuminated in red, green and yellow, indicating an occupied zone, an authorized proceed zone and a stopping zone respectively. Since a train is prohibited from passing an absolute marker without authority the zone preceding such a marker never becomes an authorized proceed zone. The signal lever, e.g. 12SL in its L.H. position allows a train in zone 14.1 to proceed into zone 12.1, in its intermediate L.H. position it allows a train in siding 14.1S to proceed into zone 12.1, in its intermediate R.H. position it authorizes a train in zone 10.2 to take siding and occupy zone 12.2S and in its R.H. position it authorizes a train in zone 10.2 to occupy zone 12.2. Associated with each zone is a RGZ or LGZ relay which when energized via the signal lever permits the entry of a train into that zone. A D or distant relay prevents the operation of the GZ relay if traffic conditions render the occupancy of the zone unsafe, the operation of the D relay is dependent on the occupancy of other zones, determined by the TRX relays and other RGZ and LGZ relays. Take siding relays TSR and leave siding relays LS are similarly protected by the D relay. Relays RST prevent the transmission of a take siding signal to a train in a zone preceding that in which the signal should be received. Proceed instructions are transmitted to the train at a carrier frequency of F3 modulated by three tones comprising a location tone applied via a location tone relay LCT which is energized via the CH relay of the appropriate check-in check-out unit and the GZ relay, a train identification tone applied via the appropriate LCT, GZ and CIR relays and a proceed tone via the appropriate LCT and GZ relays. The picking up of the LCT relay picks up a plying relay TKI which opens the circuit of a second slowacting relay TK2, the transmitter is energized via the front contact of these two relays. Train carried signalling apparatus.-In the output of the train receiver operating at frequency F3 are three sets of tuned amplifiers responsive respectively to the train identification tone, the location tone and the instruction tone. If the identification tone agrees with the train selector setting a relay ENP is energized similarly if the location tone agrees with the location determined via the check-in apparatus a relay LNP is energized. The instruction tone energizes one of two relays PST or TST, depending on whether the instruction is " proceed " or " take siding." For a proceed instruction a relay PR is operated via relays ENP, LNP and PST, for a " take siding " instruction relay TSR is operated. If the loco. operator requires a repeat signal a repeat contact in the cab is operated whereby the loco. retransmits its check-in signal resulting in a retransmission of the control signal as determined by the position of the control office signal levers. Six aspects are displayed by the cab signal G (clear), Y/Y (advance approach), Y (approach), Y/TS (take siding), R (stop) and L (energized in territory not equipped with zone control). The automatic brake application equipment comprises a magnetic receiver on the locomotive which is influenced each time the train passes the track side train stop inductor, an electropneumatic valve EPV which when de-energized applies the air brakes on the train, an acknowledgement contactor ACK which is operated when passing a zone marker, a medium speed governor GVM and a slow speed governor GVR and a brake reset contactor RC. If after issuing a proceed signal, relay PR operated, no further instructions are issued, the cab signal will initially indicate G, on passing the next marker relay PR is released and the signal aspect changes to Y/Y. At the next marker the signal aspect changes to Y and unless the train's speed has been reduced to medium (measured by governor GVM) the train brakes are automatically applied, when the train's speed has been reduced to the required value, the automatic application of the brakes is removed by operation of the contactor RC. If the next marker is an absolute marker the train is stopped, if however the marker is permissive the train may proceed at a restricted speed, in passing the marker the signal aspect is changed to R and unless the speed has been reduced to the required restricted value (as measured by governor GVR), the brakes are automatically applied, this application is removed by the contactor RC when the train's speed has been reduced to the required value.