GB1405951A - Traffic signal installations - Google Patents

Abstract

1405951 Controlling traffic signals SIEMENS AG 2 Oct 1972 [30 Sept 1971] 45263/72 Heading G4Q In a traffic signal installation wherein traffic detectors are disposed at the entrances to an intersection and serve to detect the occupation or non-occupation of an associated area by vehicles, each detector D1-D4 is associated with a measuring device M1-M4 which stores quantities corresponding to the duration of periods of occupation and non-occupation and controls the phases in accordance with criteria derived from these quantities. The measuring devices may operate by counting pulses and producing control signals when predetermined counts are attained. However, in a preferred form (Fig. 3) each measuring device utilizes capacitors. Two circuits are provided in each device. In the first circuit (upper part of the figure) capacitor C1 is charged and discharged according to the state of contacts S1<SP>1</SP> of switch S1 connected to the associated detector such that when the detector detects a vehicle the capacitor is discharged and when it detects a gap between vehicles the capacitor is charged. Resistors W1, W2 are chosen so that for normal traffic flow the capacitor charge fluctuates between narrow limits. Ultimately, when the flow is such that overall charging leads to the output of an operational amplifier V1 reaching a limiting voltage + Ug1, a comparator K1 produces a signal at output 3 for the duration of this state. In the second circuit (lower part of the figure) an arrangement similar to that of the first circuit is such that, as the time gaps between vehicles become shorter owing to traffic build-up, the output of an operational amplifier V2 becomes increasingly negative and reaches a limiting voltage-Ug2 when comparator K2 produces a signal at output 4. As shown in Fig. 2, the outputs 3 of devices M1, M3 and M2, M4 combine in AND-gates U1, U2 respectively for actuating a switch S3 to control signal pairs Sg1, Sy3 and Sg2, Sg4. Thus, only while each device M1 and M3 simultaneously supplies an output at 3 will a phase change occur. In order to provide a maximum green time, a fixed time control can be incorporated, to operate when the traffic flows across detectors D1, D3 or D2, D4 undergo pattern changes which fail to produce simultaneous signals at outputs 3. The outputs 4 of devices M1, M3 and M2, M4 pass via OR-gates 01, 02 respectively to switch S3 to control the signals when an individual signal on any output 4 is provided due to traffic build-up. The detectors D1-D4 may be inductive loops.