GB931143A - Protective system for level crossings - Google Patents

Abstract

931,143. Level crossing control arrangements. GENERAL RAILWAY SIGNAL CO. Dec. 13, 1961 [Jan. 11, 1961], No. 44613/61. Class 105. In a level crossing control arrangement in which flashing light signals are operated and half barriers lowered to halt the road traffic a short period, e.g. 20 seconds, before a train passes over the crossing, means are provided for bringing the train to a halt in the event that an obstruction, e.g. a stalled car, is detected on the crossing. The presence of a car on the crossing is detected by a supersonic detection arrangement of the type described in Specification 931,125 which includes transmit -receive transducers T-R1 to T-R3 and control apparatus 14 and indicated by the energization of relay XOR. A stalled car is indicated when relay XOR remains energized during a period determined by thermal delay units 1TH, 2TH which energize respectively relays 1TE, 2TE to prepare a release circuit for relay TEP. The track is divided into insulated sections AT, 1T, 2T, 3T and 4T, each provided with a track circuit relay TR and relays 1H, 2H are provided for the control of signals 1S, 2S. Track inductors AI, 1I are also provided which, when open-circuited, initiate the automatic stopping of trains passing thereover. In normal operation a train moving from section AT to section IT releases relay 1H which sets signal IS to danger, on entering section 2T relay 2TR is released whereby, relay 2H is released to set signal 2S to danger, relay XR is released to operate the road flashing light signal and after a short delay relay GR is released to lower the half-barriers across the road. Relays XR and GR are maintained in their released condition until track section 3T, which includes the crossing, is vacated by the train. When a vehicle stalls in the crossing one circuit for energizing relay TEP is open at back contacts 39 and 40 of relays 2TE, 1TE, respectively, so that when a train enters track section AT and releases relay ATR relay TEP releases. Release of relay TEP opens the energizing circuits of relays 2H, and XR and changes the polarity of the energizing circuit of relay 1H so that signals IS and 2S are switched to yellow and red, respectively, and a flashing light signal is given at the crossing, in addition a " lunar white " obstruction signal LW on each signal 1S, 2S is energized via back contact 41 of relay TEP. The train is thus brought to a halt before it enters the crossing. If the train enters track section IT when relay XOR has been released for the duration of the time delay determined by thermal unit 1TH only, relay TEP is released at contact 40 relay 1TE whereby the occupants of the car at the crossing are warned of an approaching train by the flashing light signal produced by the release of relay XR and an attempt is made to stop the train before collision by the release of relay 2H which switches signal 2S to danger and opens the circuit of inductor 1I.