Patent GB-1217758-A (GB)
Title: A traffic signal control system
IPC: G08G1/097
Filed: 1968-12-03
Abstract: 1,217,758. Road traffic signals. TATEISI ELECTRONICS CO. 3 Dec., 1968 [12 Dec., 1967], No. 57287/68. Heading G4Q. In a system for controlling traffic at a street intersection having a traffic actuated signal controller 51 for controlling the normal operative condition of the signals 53, means is provided for detecting abnormal illuminating conditions of the signals to stop the operation of the signal controller 51 and means is automatically operable a predetermined period of time after the stoppage to restore the operative condition of the signal controller 51. When switch 12 is closed an output pulse from differentiator 14 passes via OR gate 15 to energize a relay 16 which closes contacts 162, 163, 164 and opens contacts 160, 161. This connects a traffic actuated signal controller 51 to control the signal lamps 53. Signals are obtained on lines 1G and 2G when the green lamps on the major and minor roads respectively are lit and on lines 2Y and 1Y when the yellow lamps on the minor and major roads are lit. With no output from AND gate 8 and timers 5, 7 the output from OR gate 22 is "0" giving a "1" output from NOT gate 22 which maintains relay 16 energized. A "1" output from the OR gate 9 is obtained if two green signals occur together, or if the green or yellow signal remains unchanged for a period longer than required, the timers 7 and 5 operating to delay the signal on lines 2Y, 1Y from occurring at the input to gate 9. The changed output gate 9 and gate 22 acts to de-energize the relay 16 which disconnects the signal controller 51 and connects a fixed signal controller 52 to operate the lamps 53. The signal lamps on the major and minor streets are both rendered red or yellow at the same time or all the signal lamps at the intersection are turned off for a predetermined time before the fixed cycle control is started. In the first cycle of the fixed cycle control when the traffic signal on the minor road displays a green signal and produces a signal "1" on line 2G this sets flip-flop 25 and also sets flip-flop 24 to give a "0" input to the inhibit element 23. In the next cycle when the major street signal is turned to green the signal at 1G becomes 1 which is fed via differentiator 28 to INHIBIT element 23 which produces an output to energize relay 16. This disconnects the fixed cycle controller 52 and causes the traffic actuated controller 51 to take over control. If the cause for the abnormal signal still occurs the output from gate 9 remains at "1" so that when the output pulse from the INHIBIT element 23 disappears the relay 16 is again de-energized and the fixed cycle controller 52 takes over control again. When one signal cycle has been completed at the end of the minor street yellow signal an output pulse is produced by a NOT circuit 29 and differentiator 29 to reset flip-flop 25. If abnormal illumination takes place before the end of the first cycle of the resumed operation of controller S1 then signal S becomes "1" and de-energizes the relay 16 so that the flip-flop 25 remains set. The fixed cycle controller 52 becomes operative again and as the output from differentiator 26 remains "0" the flip-flop 24 will not be set. When the signal 1G becomes "1" at the end of the first new cycle the output from the INHIBIT element 23 remains at "0" because flip-flop 24 remains reset. The relay 16 is not de-energized so that the lamps remain controlled by the fixed cycle controller 52. The fixed cycle controller 52 is then kept operative until the abnormal condition is eliminated. The control of the traffic actuated controller 51 may be restored by manual operation of push button 32. In a modification (Fig. 2, not shown), the signal lamps are temporarily turned off on occurrence of an abnormal condition. The signals corresponding to those produced on lines 1G and 2G by the green lamps are provided by a timer (33). The system may be applied to multiphase traffic control systems.