Patent GB-980733-A (GB)
Title: Improvements in and relating to traffic control systems
Inventor: AUER JOHN HENRY
IPC: G08G1/08
Filed: 1963-02-20
Abstract: 980, 733. Road traffic signalling. GENERAL SIGNAL CORPORATION. Feb. 20, 1963, No. 6806/63. Heading G4Q. [Also in Divisions H3 and H4] A traffic signal control system comprises a detector for at least one approach to an intersection, which assumes a distinctive condition throughout the time that a vehicle is within a detection zone; a traffic density measuring means governed by the detector for producing an output proportional to the occupancy of the detection zone; and means controlling the duration of display of a go signal to traffic approaching the intersection over that approach in proportion to the output signal. Density measuring equipment, Fig. 3. The detector of the type described in Specification 931,125 employs sound energy pulses generated by a generator 11 which is triggered by multivibrator 10. The generator pulses are transmitted by transducer T and the time interval between a transmitted pulse, and are received at R is determined by the presence or absence of a vehicle. When no vehicle is present, received pulses are fed via gated amplifier 18 to set the bi-stable circuit 19 in one state. Presence of a vehicle causes a pulse to be received at a different time, and to be fed via gated amplifier 17 to set the bi-stable circuit to its other state. The bi-stable circuit sets relay RN into one or other of its states, the duration in which it is maintained energized thus depending on the occupancy of the measuring zone. Controller, Fig. 4. Separate detectors are associated with each of the four approach roads to the junction, to control separate relays RN, RS, RE, RW. These relays control the charge on capacitors, e.g. 28, to produce a potential proportional to the occupancy and the occupancies of the North and South roads and the East and West roads are summed to produce voltages at 51, 52 respectively proportional to the average occupancies. Alternatively the voltages at 51, 52 may be made proportional to the larger of the two occupancies, Fig. 4A (not shown). The traffic control lights are switched cyclically under the control of relay 30 to give four phases, green East-West, amber East-West, green North-South, amber North South, producing voltages on lines 31, 32, 33, 34 respectively. Assume the condition with a voltage on line 34 energizing relay A2 and giving an amber signal on the North-South road. Relay AP is energized and capacitor 41 is charged from a potential determined by the setting of potentiometer 42 when the capacitor 41 becomes fully charged valve V2 becomes conductive cutting off valve V3 and releasing relay T1. This energizes relays T2 and 30 stopping the controller to phase 1 in which the green East-West signals are lit, and energizing relay PG1. The discharge circuit for capacitor 45 is now open, so that this capacitor charges via resistor 52 until valve V4 conducts re-operating relay T1 and releasing relay T2. The voltage representing the average occupancy of the East- West lanes is now fed from 52 via capacitor 41 to cut off valve V2 for a time dependant upon the occupancy of these lanes. Valve V3 is switched on and holds relay T1 operated after capacitor 45 has discharged sufficiently through contact 51 of the now released relay T2 to cut off valve V4. When capacitor 41 is charged valve V2 again becomes conductive and the cycle repeats switching the controller to its next phase. The duration of each phase is thus determined by the charging potential applied to capacitor 41 so that the duration of each green phase may be varied from a minimum with no occupancy to a maximum with 100% occupancy, the minimum and maximum valves depending on the settings of the potentiometers 26, 27. Failure. The pulses from relay T2 operating relay 30 are also fed to a relay FT which is maintained energized as long as pulses are received at the normal rate. Failure of a pulse due to a fault allows relay FT to release connecting an internal timer 60 to control the relay 30.