Patent GB-725475-A (GB)
Title: Improvements in or relating to traffic control systems
Inventor: RANGE ALAN LESLIE
IPC: G08G1/08
Filed: 1953-05-15
Abstract: 725,475. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 15, 1953, No. 13597/53. Class 118 (2) [Also in Group XL (c) ]. A traffic control system of the vehicle-actuated type for controlling traffic at the intersection of a plurality of traffic lanes comprises two vehicle detectors in each approach to the intersection, the detectors being spaced apart a distance less than the length of a normal vehicle in the direction of traffic flow and being arranged to control a timing device which extends the right-of-way period to a traffic lane already possessing it by an amount inversely proportional to the speed of a vehicle traversing the detectors; the system is also arranged so that no control is exercised by the detectors unless they are operated in the appropriate order. The system may employ spaced pneumatic detectors of the type described in Specification 653,900 which-actuate detector contacts DCA and DCB in succession when traversed by an approaching vehicle and it is described as using a timing circuit V1-V3 of the type disclosed in Specification 690,503 comprising a 1,000 c/s oscillator V1 and a triode V2 having in its anode circuit a relay T which when released connects positive over contacts T2 to lead TRW to terminate the right-of-way for the traffic phase using the timer and connects positive via resistor R4 and contact T1 to rapidly charge capacitor C2 thereby rendering V2 conductive to operate relay T which opens contacts T1 and T2. The opening of contact T1 causes the grid of VI to become abruptly negative with respect to its cathode, the valve cuts off and the negative grid potential decreases exponentially at a predetermined slow rate to a positive value determined by the potentiometer R7. This period constitutes the minimum period for the running phase and if during this period a demand is registered by the halted phase, the disabling contacts STI are opened so that when the grid of V1 reaches its normal positive bias, the valve oscillates and the negative half cycles of its output are applied via rectifier MRA to the grid of V2 thereby cutting off V2 and releasing relay T to initiate another cycle. According to the present invention the operative time of the running phase is extended when the detector contacts DCA, DCB are successively actuated to operate high-speed relays HSA, HSB respectively which by means of contacts HSA1, HSB1 cause a large capacitor Cl to be charged via resistor R2 during the interval between actuation of the detector contacts and then connected for a short period to the timing capacitor C2 whose charge, and hence discharge period, is thereby increased by an amount inversely proportional to the speed of the vehicle actuating the detector contacts. As shown two conventional telephone-type relays A and Bare also energized by the detector contacts over their right-hand windings to close holding contacts A2 and B2 for the high-speed relays and to operate contacts Al and Bl which short circuit the left-hand windings of relays A and B causing them to have slow release characteristics; contact B1 also disconnects the operating windings of relays A and HSA so that if detector contact DCB is actuated first relays HSA and A cannot operate, i.e. the detector relay circuit is uni-directional. As applied to a system of the type disclosed in Specification 512,439, detector contacts for each phase are connected to the detector relay circuit via changeover contacts PR1, PR2 of the relevant phase relay.