415,852. Road systems for controlling traffic. OPEL, F. VON, 33, Bismarckstrasse, Charlottenburg, Berlin. April 26, 1933, Nos. 12195, 12196, 12197, and 12198. Convention dates, April 26, 1932, Sept. 17, 1932, March 9, 1933, and April 1, 1933. [Class 118 (ii).] An automatic control system for traffic at road intersections comprises the following features, (1) the frequency of the cycles of switching operations controlling the signals is subject to continuous variation taking into account simultaneously the traffic density in the intersecting roads by using the ratio of the densities to determine the periods of the signals ; (2) as the number of vehicles collected in the control space of the blocked road over-emphasizes the density in that road, the density of the traffic in the free street is taken as the observed density increased in the ratio of the mean between the numbers of vehicles which would be present in the control space of a blocked road at the beginning and end of a period to the number which would be present in the control space of the free street, assuming an equal number of arrivals in both streets and a certain average speed ; (3) the frequency of the cycles is varied by changing the speed of the driving means of the switching gear, e.g. an electromotor, self-stepping relay, or clockwork, by brakes or variable resistances, separate logarithmically tapped resistances for the blocked and free streets being connected in a motor circuit so that control by the density ratio as in (1) is obtained ; (4) different sets of resistances may be switched in manually to adjust the system ; (5) a fixed overriding maximum time period is provided for the red and green signals and a variable minimum is controlled by the number of vehicles present in the blocked road when freed; (6) a fixed period warning (amber) signal; (7) two counting gears, one always associated with the free road and the other always with the blocked road, the counters being electrically or optically operated, but, as described, operated by electromagnetic waves from the vehicles ; (8) the counter of the free street is stepped back once for every vehicle passing therefrom over the intersection (the arrangement described gives an approximation to this) and when the free street becomes blocked the number in its control space is transferred to the counter of the blocked street. Operation. The motor 1 drives the mechanism (not shown) for changing the lights and also the drum 2 of a sequence switch which controls contacts indicated by a bar above the reference, e.g. 5. The motor is supplied over terminals 3, 7 and a hand or clock-controlled switch 4 and during the amber period (5 down) its circuit includes only a resistance 6 (adjustable by hand) so that the speed of the motor is not dependent on traffic conditions. During red and amber periods, the circuit of the motor passes over switch 10, variable resistance 12, hand-adjusted resistance 13, switch 14 and variable resistance 15. Magnets 23, 24 of the switches 10, 14 are impulsed by the road relays 17, 18 of the two roads, their circuits being controlled by drum contacts 26, 27 so that the relay of the blocked road always pulses magnet 23 and the relay of the free road always pulses magnet 24. As shown, relay 17 is in the road at present blocked, and impulses therefrom step 10 to cut down resistance 12 in logarithmic steps while relay 18 of the free road steps 14 to increase resistance 15 in a similar manner. When a road is freed, it must remain free for a minimum time dependent on the number of vehicles that have accumulated between the counting device and the cross roads. The hand-adjusted resistance 13 provides a lower limit for this minimum and a switch arm 34 and potentiometer 35 determines the period in accordance with the number of waiting vehicles, switch arm 34 being rotated with arm 10. When red changes to amber, 38 is temporarily made to charge condenser 36 in accordance with the setting of the potentiometer 35, and when green comes up, 39 connects one side of the condenser to the grid of valve 41 which passes current over relay 42 for a period dependent on the charging voltage and the value of grid leak 40. Relay 42 introduces additional resistance into the motor circuit. In order that the counting switch 14 of the free road may take account of the vehicles which have passed out of the control section since the road was freed, a relay 43 operated in parallel with magnet 24 of the switch 14 (44 is open only when amber is showing), charges up condensers 49 over a wiper 46 of a switch 46, 47 stepped continuously by magnet 61 under the control of a self-interrupting relay 59. The wiper 47 is displaced backwardly relatively to 46 by an angle dependent on the average time taken by a vehicle to pass through the section, and in due course discharges any charged condensers 49. The resultant impulses on the grid of valve 52 are repeated by relay 53 to magnet 55 which back-steps the switch 14. When green changes to amber, 30, 33 complete homing circuits over wipers 28, 31 of switches 10, 14. Shortly after the change, 57 opens to speed up the self-interrupting relay 59 and 56 connects up magnet 23 of the blocked road counter, and the number of vehicles in the control section of the road that has just been blocked, as indicated by the number of charged condensers 49, is rapidly transferred to switch 10. Vehicle detectors. A conductor laid across the road serves as an antenna 66, Fig. 3, for receiving electromagnetic radiations from the vehicles. The impulses from passing vehicles are rectified in an ordinary receiver 65 connected to an amplifier 68 having a relay 72 in its anode circuit which repeats the impulses to the counting device 75. Relay 72 may be slow-torelease to prevent double counting of each vehicle since, as stated, the relay receives an impulse during the passage of each axle. A second relay may be interposed between relay 72 and the counter. If the conductor is laid obliquely across the road, a slow-to-release relay is unnecessary.