Patent GB-1217693-A (GB)
Title: A traffic signal control system
IPC: G08G1/08
Filed: 1968-02-07
Abstract: 1,217,693. Road signals for controlling traffic. TATEISI ELECTRONICS CO. 7 Feb., 1968 [14 Feb., 1967], No. 5974/68. Heading G4Q. In a system for controlling traffic signals at an intersection of a plurality of streets the number of vehicles passing a vehicle detector 42, 46; 44, 48 in a predetermined first period of time is counted and traffic volumes are obtained by counting the number of vehicles passing the detector in a predetermined second period of time substantially longer than the first period of time and means is operable in response to a predetermined number of vehicles on the street to which a red signal is given being detected in the predetermined first period of time such that a green signal is given to allow the traffic to pass to the intersection. As shown major street detectors 42, 46 and minor street detectors 44, 48 feed signal generator and pulse counters 49, 50 which supply outputs L1, L2 indicating the volume of traffic on the major and minor street to a comparing circuit 51 which gives an output if the volume on the major street is greater than that on the minor street. Also outputs LM and LC are given when the vehicles counted on the major or minor street reach the predetermined number. The outputs LM, LC are fed to bi-stable circuits F1, F2 via INHIBIT logic elements IN1, IN2 depending on the condition of the AND gates A1, A2, A3 and NOT gates N1, N2. The output from the bi-stables F1, F2 are passed via OR gate OR2 to a controller 52 which controls the operation of the traffic lights at the intersection. The signals on lines LY, L1G and L2G are "1" when the yellow; major green, minor red; and minor green, major red signals are illuminated. If the predetermined number of vehicles is detected on the major or minor street when these are giving a green signal although the signals LM, LC cause the bi-stable F1 or F2 to be set to give a "1" output as the lines L2G, L1G are "0" this does not affect the input to the OR gate OR2 and the signals on the major or minor street remain unchanged at green. However if the major or minor street signal is red on occurrence of the predetermined number of vehicles waiting on the major or minor street than the signal changes to green. The change in the traffic signal may be effected the instant signal S becomes "1" or a short period of time after by including a delay element between OR gate OR2 and the controller 52. Alternatively the change in the traffic signal may take place upon termination of the initial portion of the green signal or by shortening the unit extension to be added, for every one vehicle detected, to the initial portion of the green signal. If a signal LM and LC occur together but the traffic volume on the major street is smaller than that on the minor street the signal LM is prevented from setting bi-stable F1 whereas signal LC passes to set bi-stable F2. If the green signal is displayed to the major street then this is changed to red and green is given to the minor street. Alternatively if the major street is red then it stays at red and the minor street stays at green. Similarly if signals LM and LC are both received together and the traffic volume is greater on the major street than the minor street or if the major street priority command is given on line LP2 the signal LM controls the bi-stable F1 and controller 52 to give a green signal to the major street. The yellow signal supplies reset inputs to the bi-stables F1, F2. The logic elements A, IN, N, OR and F may include diodes and/or transistors. The system may be used in a multiphase control system. Four signalling devices (32, 34, 36 and 38, Fig. 1, not shown), are located at the intersection and each signalling device has a green, yellow and red lamp arranged from left to right.