Patent GB-1018752-A (GB)
Title: Traffic control system
IPC: G08G1/082
Filed: 1962-08-31
Abstract: 1,018,752. Road traffic signals. LABORATORY FOR ELECTRONICS Inc. Aug. 31, 1962 [Sept. 1, 1961], No. 33593/62. Heading G4Q. In a traffic control system comprising a master controller and several local controllers, one or more characteristics (e.g. offset, split or cycle length) of the local or master cycles is controlled by two different traffic measurements. The system may be of the type wherein a master controller produces a three-phase reference signal FR of 400 c/s. and a three-phase control signal FC of slightly different frequency, the frequency difference determining the cycle length and being controlled by traffic volume measurements in each direction along a main road, Fig. 1 (not shown). In the local controller shown in Fig. 6 the signal FR is phase-shifted by unit 32 in accordance with an offset signal on line 13 derived from the master controller. The signal FC is phase-shifted in unit 60, which is controlled in accordance with traffic volume in the side road, assumed to lie East-West. The output of unit 60 is further phase-shifted in unit 33 controlled by line 13. In the first position of line switch 31 the outputs of phase shifter 32 and 60 are compared in phase comparator 34 which produces an output on line 50 when the phases coincide. This output moves the line switch to its second position where the outputs of phase shifters 32 and 33 are compared and, on coincidence, move the line switch back to its first position. The line switch controls the traffic signals 51. In another arrangement, Fig. 7, the offset signal on line 13 causes either or both relays 47 and 68 to operate thereby supplying the signal FR to a selected one of three preset potentiometers A, N and S corresponding to average, northbound preference and southbound preference. The signal FR is also supplied to the stator 57 of a differential generator 56; the output from the rotor 58 of the generator is compared in unit 64 with the output from the selected potentiometer A, N or S, and any phase difference detected causes a motor M to drive the rotor slowly (e.g. over several signal cycles) and by the most direct route to equalize the phases. The system of Fig. 7 is otherwise the same as Fig. 6 except that the phase shifter 33 determining the split is controlled by a signal on lead 80 which results from comparison of E-W traffic with N-S traffic. Grid control system.-When the road system comprises three N-S avenues A-C intersecting three E-W streets 1-3 with a local controller LC at each intersection, Fig. 10, the system may be controlled from four traffic measurements to combine a desired N-S preference with a desired E-W preference. The detectors 100- 103 may respond to traffic volume, density, or speed, and units 108 and 109 calculate the desired cycle lengths and offsets. The system selector 114 responds to the outputs of units 108 and 109 to select the required cycle length and to provide the split control on line 80 described in Fig. 7. The local controllers on avenue A are provided with the reference frequency FRA and control frequency FC from unit 116 and with the N-S offset signal from unit 108 which is supplied to all the local controllers. The reference frequencies FRB and FRC supplied to the controllers or avenues B and C are phaseshifted in transposer units 120 and 130 to provide desired E-W preferences. The transposer units 120 and 130 (Fig. 11, not shown) are generally similar to unit 32 of Fig. 7. In accordance with a signal on line 113 either or both of two relays are energized, according to whether Eastbound preference, Westbound preference or average offset is required. In accordance with the relays the input signal FR is directed to one of three banks of six potentiometers; selection of one of the six potentiometers in each bank is controlled by a signal on line 112 in accordance with traffic volume. In this way the signals FRB and FRC may be subject to one of 18 predetermined phase shifts in accordance with the outputs of system selector unit 109.