Patent GB-1230249-A (GB)
IPC: G08G1/081
Filed: 1969-05-09
Abstract: 1,230,249. Road signals for controlling traffic. SUMITOMO ELECTRIC INDUSTRIES Ltd. 9 May, 1969, No. 57674/69. Heading G4Q. In a road traffic control system for a district having a plurality of road sections with signalized intersections at both ends, a tree pattern of road sections is determined by an offset effect circuit which receives output signals from a traffic volume and density determining circuit and which selects offset effect values in the manner as claimed and disclosed in the Specification 1,187,054, providing offset values to the signals controlling the sections forming the tree so that the travel time along the selected tree in both directions is minimized, and a district controller including the traffic volume and density determining circuit selects the offset, split and cycle times for application to local controllers controlling the signals at the intersections. District controller, Fig. 12.-Information from traffic detectors TD is received in traffic information device 1201 (Fig. 20, not shown) which feeds a traffic counter 1202 (Fig. 20, not shown) giving volume and density values. Cycle length selector 1205 (Fig. 21, not shown) and split selector 1026 (Fig. 23, not shown) then determine the values for cycle and split according to the traffic flow from previously prepared values. The offset selector 1207 (Fig. 22, not shown) for a district controller DC1 in a district with no closed loops and shown in Fig. 25 for a district controller DC2 having closed loops, selects the required offset values. The local controller LC is fed with these cycle, split and offset values via 1209. In a district controller DC2 (Fig. 25) the traffic pattern is detected by a detector 2501 and if a previously determined traffic pattern is detected the shape of the required tree sections are then selected by OR gates 2519-2521 and are memorized in flip flops 2540-2542 so that the offset selecting circuits 2545-2547 issue up or down preference or balanced offset signals. If none of the previously prepared traffic flow patterns is detected then the tree is selected by the maximum traffic volume road section extracting circuit 2502 and closed loop detector 2503. Signals representing the swing of the traffic volumes in both directions are applied at 2522, 2552 and these are converted to offset effect values by setting variable resistor 2523-2524. The road section having the maximum offset effect value is determined in a MAX circuit 2525 and the corresponding comparator 2526-2529 gives an output to select that road section for the tree. This process is repeated to determine a tree as described in the Specification 1,187,054. Circuit 2503, which includes bidirectional gate circuits, prevents a road section being selected if a closed road loop would be formed. The absolute offset values for the signals at each intersection are obtained from circuits 2555. Central controller (Fig. 26, not shown).-The central controller compares traffic volumes in a flow pattern detecting device (2605) and obtains the offset values in the same manner as the district controller at 2501, Fig. 25, for tree sections to be formed crossing one district into another. The central controller specifies cycle, relative offset and split values within each district or districts. Also the traffic flow is indicated by a lamp indicator (2681). Switching circuits (2609, 2635 and 2636) and timing circuits (2655-2657) then control the signals. It is possible to provide manual control by switches associated with the switching circuits (2609, 2635, 2636). Local controller (Fig. 19).-The local controller is at each intersection and has a timer 1909 including a capacitor 1911 storing charge, a field effect transistor 1913, comparing circuits CMP and monostable circuits MM. The outputs 1924, 1923 of these monostable circuits control the start of the main green signal and amber signal in the secondary direction. A similar timing circuit 1925 controls by outputs 1926, 1927 the end of the green and amber periods. Switching circuit 1928 switches the lights. Vehicle detectors (Fig. 17, not shown).-A loop traffic detector (1701) feeds an oscillator (1702) and the change of output frequency of this oscillator when a vehicle is detected is fed via a frequency discriminator circuit (1703) to a modulator (1704). Similarly the modulator (1704) is fed with other inputs and its output is sent to the district controller. The vehicle detectors may be responsive to electrostatic capacity, pressure, mechanical, supersonic or electromagnetic variations. Cycle length selector (Fig. 21, not shown).- The maximum flow in at the intersections are compared in comparers (CMP) with reference values provided by a circuit (2134). The value of the cycle is selected in a level setting gate (2139). This feeds an oscillator (2148) and a frequency step-down circuit (2149) to provide a reference cycle value. Gate circuits (2160- 2164) enable the central controller to take over and inhibit the output from the circuit (2149).