Patent GB-1022193-A (GB)
Title: Traffic control system and apparatus
IPC: G08G1/081
Filed: 1962-09-17
Abstract: 1,022,193. Road traffic signalling systems. LABORATORY FOR ELECTRONICS Inc. Sept. 17, 1962 [Sept. 18, 1961], No. 35370/62. Heading G4Q. A traffic control system includes a master controller 20, Fig. 1, comprising a separate traffic volume (or density) measuring circuit for the inbound and outbound traffic respec tively, and also, for each direction of traffic flow, (a) three response circuits responsive respectively to progressively higher levels of traffic volume and (b) a difference circuit which responds when the corresponding directional traffic volume exceeds that of the other traffic flow by a predetermined amount. The " offsets " required are determined by the difference in the traffic flows while the signal cycle lengths are selected by the response circuits. Master controller (Fig. 2a).-The inbound and outbound traffic flows are sensed by detectors 33, 34, respectively. Operation of detector 33 energizes a relay 64, which as described later, results in a voltage proportional to the inbound traffic volume being applied to a line 120 and read on a meter 121. Relays 65, 67, 68 in response circuits 51, 52, 53 operate in succession when this voltage reaches progressively higher values. Response circuits 51<SP>1</SP>, 52<SP>1</SP>, 53<SP>1</SP> respond similarly to progressively higher values of outbound traffic volume which is similarly measured, indicated on a meter 121<SP>1</SP>, and represented by the voltage on a line 120<SP>1</SP>. The voltages on lines 120, 120<SP>1</SP> are also applied to both difference circuits 54, 54<SP>1</SP> associated with the inbound and outbound traffic respectively. These circuits are adjustable so that when the difference between the values of the two traffic flows exceeds a predetermined limit the difference circuit associated with the higher traffic flow responds and energizes its relay 66 or 66<SP>1</SP>. Both traffic volumes below predetermined limit. Relays 65, 65<SP>1</SP> and 66, 66<SP>1</SP> are de-energized and the " translating component " of the master controller transmits signals to the local controllers so that the latter cycle free in any " offset " or an " average offset " condition according to the position of a manually operable selector switch. With increasing traffic flow in both directions relays 65, 65<SP>1</SP> are energized to signal " average offset " conditions to the local controllers. When one traffic flow greatly exceeds the other relays 65, 66 will be energized and 66<SP>1</SP> deenergized (65<SP>1</SP> may or may not be energized), or vice versa, and a call for " inbound preferential offset " or " outbound preferential offset " sent to the local controllers, whichever is applicable. As the traffic increases the successively operated relays 67, 68 or 67<SP>1</SP>, 68<SP>1</SP> in the response circuits operate and selectively operate motors to control the timing of the signal cycle by the local controllers. Circuit for determination of traffic volume. Fig. 2a.-Capacitor 85 is initially charged to a voltage tapped off potentiometer 86. On energization of relay 64 contacts 83 are opened and 84 closed and capacitor 85 discharges into capacitor 95, the accumulated charge on which is discharged through an adjustable discharge circuit to junction 101. Adjustment of tap 100 provides for the allowable 100% value of vehicle volume. The charge on capacitor 95 is also applied to triode 91 and the instantaneous traffic volume measured by the voltage at 104. A long-term average volume over six different time intervals depending on the position of switch 109 is obtained in circuit 106 and is applied to a cascaded cathode follower 112, 113. The voltage at 120 is therefore a measure of the volume of detected traffic averaged over a time period selected by switch 109, and is shown on meter 121. . Response and difference circuit operation.- When the voltage on line 120 representing the volume exceeds a predetermined limit (set in potential dividers 131-135) triode 140 conducts and energizes relay 65. The voltage on line 120 is also applied to the grid of a triode 70<SP>1</SP> of the difference circuit 54<SP>1</SP> of the outbound traffic system, an equivalent connection being made from the outbound traffic difference circuit 54<SP>1</SP> to the inbound difference circuit 54. Energization of the relay 66 is controlled by triode 71, the grid voltage of which is controlled by the volume voltage at 120 via potentiometers 150 . . . 152 and resistor 153, and the cathode voltage by the outbound volume voltage from circuit 54<SP>1</SP>, so that triode 71 becomes conductive when the difference exceeds a predetermined amount. The difference circuits respond to a constant pre-set numerical difference so that they respond to a decreasing percentage volume difference as the volumes increase. Circuits operated by relays 65-68, 65<SP>1</SP>-68<SP>1</SP> (Fig. 2b).-These relays operate respective contacts 65-5, 65<SP>1</SP>-5, 66-5, 66<SP>1</SP>-5, ... &c. and control relays 171, 172, 175, 176. The master controller signals to the local controllers to effect one of several signal cycle offsets by the absence or presence (in combination) of signals on leads 191, 192 under the selective control of relays 65, 65<SP>1</SP>, 66, 66<SP>1</SP>. Power is simultaneously applied to corresponding selective combinations of terminals 1-6 according to the various " offsets " called for. Different signal cycle times are selected by the operative relays 67, 67<SP>1</SP>, 68, 68<SP>1</SP> which control relays 175, 176 to select which one of three cycling motors M1, M2, M3 shall operate. The selected motor runs for one cycle (i.e. the selected cycle time) during which the signals from the master controller are " frozen." The effective " cycle time " is signalled to the local controllers over the selected one of leads 193-195. Details of the operation of timing cam contacts at the local controllers by the motors are given (Figs. 3, 4, not shown). Three motors are provided at each local controller each driving several cams and may each provide three different cycle lengths, selected by the master controller according to the amount of traffic and any one of three " offsets " plus " free " coordination may be selected according to the relation between the traffic flows. The control possibilities are extended by appropriate selective connections of the jumpers J-1 to J-4, to the terminals 1-7.