Patent GB-1003412-A (GB)
Title: Traffic actuated control system
IPC: G08G1/08
Filed: 1961-09-11
Abstract: 1,003,412. Road traffic actuated signalling systems. LABORATORY FOR ELECTRONICS Inc. Sept. 11, 1961 [Sept. 12, 1960], No. 32568/61. Heading G4Q. A traffic light 1 is situated at an intersection (Fig. 1) of a road having lanes 3, 4, 5, 6 (phase B) and one having lanes 11, 12, 13, 14 (phase A). Vehicle actuated detectors DAN1, DAN2 in lanes 11, 12, DAS1, DAS2 in lanes 13, 14, DBE1, DBE2 in lanes 3, 4 and DBW1, DBW2 in lanes 5, 6 each include a lane timer. Each timer receives information from its respective detector and.from all the detectors in the other phase. The output from each timer is fed into a sequence comparison unit which compares the output of all the timers from the " green " phase and the output of the comparison unit fed to control the traffic lights is the one corresponding to the longest extension period of the " green " phase as determined by the incoming signals from the timers to the comparison unit. The comparison unit serves only that phase which is green. The factors determining the length of the green phase of each lane (subject to an over-riding maximum) area: (1) the gap between vehicles; (2) the traffic density; (3) the waiting period of the first car in the red phase; (4) the number of cars waiting in the red phase; (5) the total elapsed time; (6) after the control signal has shifted from green to red, the number of vehicles between the detector and the intersection in the green phase. Each lane timer allows an initial minimum period of green time proportional to the number of cars which passed the detector during the preceding red period and an extended green period increased in response to further cars actuating the detector in that particular lane and decreased according to the number of cars waiting at red in the other direction. The control signal for a change from green to red from the timer to the sequence comparison unit is given when the actual time gap between successive vehicles exceeds the permissible time gap, i.e. the lane needs no more green time (always subject to the maximum of the extendible period). The green signal will not actually change, however, until all the timers of the same phase have indicated that they need no more green time. Timing unit circuits.-The gap-timing circuit (Fig. 5) of each lane timer unit consists of the parts shown. The gap is measured by an R.C. circuit 118, 119, the capacitor 119 being discharged every time normally open detector contact 128 is closed by a car. The output from the capacitor 119 is fed to first, second and third comparator units. The average volume density circuit provides an output on line 157 to the first comparator unit which includes a tube 173. The circuit parameters of the volume density are so adjusted that the potential on line 157 increases to a value just below the most positive peak on line 127 so that as the number of vehicles per unit time decreases the potentials on lines 157, 127 will approach each other until tube 173 triggers and operates a relay 175 to provide an output from the timer to the sequence comparator unit that no further green time is needed (Fig. 6, not shown). The other comparator units compare the voltage on line 127 with the outputs from the " time waiting " and " number of cars waiting " units to trigger tubes and relays in the respective comparators. If any of the tubes are triggered the detector contact 128 is shorted. A circuit (Fig. 8, not shown) actuated according to the number of cars waiting at the red light in the other phase, is connected to lead 215. After all the lane timer circuits have signalled that no further green time is needed, the passage time circuit (Fig. 10, not shown) will determine the additional time which must elapse before the end of the green cycle of the phase. Details of the interconnection between the lane timers and of the method used to indicate that no more green time is needed are given (Fig. 7, not shown). The sequence comparison unit, Fig. 11, includes a step-by-step switch L.S. which controls the red (R), yellow (Y), green (G) signals through the contacts of relays AB, GY, the R, Y, G signals of phase A being connected to lines 500, 499, 498 and those of phase B to lines 501, 496, 497. The step-by-step switch provides: a circuit to time the minimum initial green portion, the yellow interval for each phase, and to act as a comparison unit, the circuit includes switch banks 6, 6, relay AS, tubes 448, 453, 455. Position 1 is a skip step, position 2 is the minimum green for phase A, position 3 a skip and rest position, position 4 is the extendible green of phase A, position 5 the clearance interval for phase A, positions 6-10 are the corresponding positions for phase B in the reverse order. The minimum green time circuit includes a timing capacitor 447 and the relay AS which when energized advances the switch LS to position 2, when bank 6 connects the minimum " green " resistor 442 into the circuit of capacitor 447 while bank 5 connects a capacitor 452 to the lane timers. When the required " green " has been timed, the switch advances to position, 3 where it rests unless there is a call from phase B, when it advances to position 4. The lane timer still having the longest time to go controls the voltage on capacitor 452, and the extendible " green " portion of phase A is terminated by triggering of tube 453 actuating relay AS to step the switch to position 5 which is the clearance interval.