Patent GB-674590-A (GB)
Title: Improvements in or relating to traffic actuated control apparatus
IPC: G08G1/082
Filed: 1950-08-16
Abstract: 674,590. Road signals for controlling traffic. EASTERN INDUSTRIES, Inc. Aug. 16, 1950. [Aug. 16, 1949] No. 20.297/50. Class 118 (ii). The invention relates to a progressive traffic control system in which the cross-traffic periods at successive intersections along a highway are offset to come 'in a progressively later times, different offsets being provided for conditions of predominate inbound and outbound traffic, flow and an average offset being employed for best two-way movement. In accordance with the invention, two cycle selectors with associated traffic actuated detectors are provided, one to sample the inbound and the other the outbound traffic flow, the length of the time cycle of the system, and the selection between inbound offset, outbound offset and average offset being made in accordance with the relative setting of the two selectors. The selectors may for example have six settings corresponding to six levels of flow. When both selectors are on the same setting, the average offset is chosen, but when the selectors differ by a preset number of settings, the offset forming the heavier traffic flow is selected. When both selectors are on the lowest setting, indicating very light traffic flow, the signals at the individual intersections, where provided with local traffic detectors, may be released for independent operation. The apparatus comprises a master controller, Fig. 3, embodying the cycle selectors and offset selecting mechanism, and individual traffic signal controllers, Fig. 7, each with an associated local cycle-offset unit, Fig. 6. The length of the time cycle is controlled by varying the frequency of supply applied from the master controller over lines VCC-1, VCC-2 and the offset-is selected by appropriate energization of lines ICC, OCC. Master controller, Fig. 3. Cycle selector ICS with associated traffic detector DDI determines the inbound traffic flow during periods of six minutes under the control of a sampling period timer CST, Fig. 4, (not shown), and indicates the level by applying A.C. power to one of six output circuits AI-FI. Cycle selector OCS and detector DDO operates similarly to indicate outbound traffic flow by applying power to one of circuits AO-FO. In this manner one relay in each of the series IA-IF and OA-OF is operated and dependent upon the higher setting of the two selectors, alternating current is applied from the positive line through line 13 and the relay contacts ib5, 6-if5, 6 and ob5, 6-of5, 6 to one of the lines ACG-FCG extending to a cycle generator unit CG. In the case illustrated, where selector OCS is set at level E and selector ICS at level C, relays OE and IC operate and line ECG'is energized in accordance with the higher setting E of selector OCS. The cycle generator CG, Fig. 5 (not shown), comprises an alternating current generator driven by a motor connected in series with a potentiometer on which are taps brought out via lines ACG-FCG. Line ACG connects with the lowest resistance tap so that the higher the setting of the selectors the lower will be the motor speed. The variable. frequency output appears on lines VCC-1, VCC-2, Fig. 6, a regulator being connected across the lines to maintain the voltage constant irrespective of frequency. Alternative forms of cycle generator may employ six timing motors for the six available time cycles, or electronic variable frequency generators. The selection of offset is determined by which contact in each of the series ia7-if7, oa7-of7, is closed. The contacts connect tappings on a potentiometer R1-R5 connected across a low voltage A.C. supply LV to the ends 1, 2 of the primary of transformer TH and so determine the polarity and amplitude of the potentials applied to the grids of triodes IV, OV. If the two selectors are at the same setting, the same tapping is connected to each end of the transformer and no potential appears on either grid. If, however, the selectors differ in setting, a potential appears on each grid and dependent upon which selector is at the higher setting, the voltage on one grid is in phase with the anode voltage and causes the triode to conduct whilst a that on the other grid is out of phase with the anode voltage and prevents the triode from becoming conducting. In this manner relay OR is caused to operate when the selectors differ with the outbound selector at the higher setting and relay IR caused to operate when the inbound selector is at the higher setting. The relay contacts iv4, ov4 control the application of potential to the offset control lines OCC, ICC. For outbound offset line OCC alone is energized, for inbound offset line ICC alone is energized and for average offset both lines are energized since neither relay IR nor OR is operated. If both selectors are on their lowest setting indicating light traffic flow in both directions relay IA and OA are operated and contacts ia8, oa8 de-energize both lines. This condition may be employed to free the traffic controllers from independent operation. If, however, it is desired to retain control by the master unit, switch SW1 may be closed to short-circuit relay contacts ia8, oa8. The number of settings separation between the two cycle selectors required to make one of the triodes conduct is adjustable by potentiometer P1 controlling the cathode potential of the two triodes. To increase the stability of the system against too frequent shift of offset under rapidly varying traffic conditions, the separation required to change from the average to a preferential offset may be made greater than the separation required to maintain the preferential offset against change back to average offset. To effect this, switch SW2 is opened to that resistor P2 is connected in series with potentiometer R1-R5. When either relay IR or OR operates, contact ir7 or or7 short-circuits resistor P2 and causes an increased potential to appear across potentiometer R1- R5. If, for example, a difference in setting of two is made necessary to render either triode conducting with resistor P2 in circuit, the triode may be held conducting with a difference of only one when P2 is short-circuited. Where cycle selectors are employed of the type having six-step switches which are stepped forward rapidly five positions to produce the equivalent of stepping backwards one position, an additional make contact is provided in each selector mechanism, Fig. 4 (not shown), which is operated when the selector is stepping down to complete a circuit extending through wire 53 to relay SD. Relay contacts sd in association. with contacts iv4-iv6 of relay IR and contacts ov4-ov6 of relay OR maintain the previously established conditions of conduction and non- conduction in triodes IV and OV so that the artificial transient conditions produced during the stepping of the selectors do not change the offset control conditions on lines ICC, OCC. Relay SD is dispensed with when cycle selectors employing reversible stepping switches are used. Local cycle offset units, Fig. 6. A unit is provided for each intersection, the units differing only in the position of cams 1CA, 1C1, 1CO to provide offsets individual to the intersection. The cams are rotated. by synchronous motor 1M energized via amplifier 1AM from the variable cycle lines VCC-1., VCC-2. Release of the traffic controller 1TC for cross traffic operation is effected via lead 1PC which is connected to earth for a selected portion of the cycle via contact 1S1, 1S2 or 1S3. Cam 1CO actuating contact 1S3 is selected for outbound offset, cam 1C1 and contact 1S2 for inbound offset, and cam 1CA and contact 1S1 for average offset, the selection being made by relays 1AR, 1BR operated in accordance with the energization of the offset control lines OCC, ICC by the master control unit. Under light traffic conditions when both of lines OCC, ICC are disconnected, relays 1AR and 1BR are released and earth is applied continuously to line IPC via contacts 1bv4 and 1av6. Cam 1CR operating contact 1SR functions in conjunction with relay 1RS connected to line RSC to synchronise motor 1M with a similar motor, Fig. 8 (not shown) in the master control unit. This ensures that a local cycle offset unit which has got out of step, due for example, to a power failure is resynchronised with the master unit. If it is desired to switch the offset control on a common basis, the relays 1AR, 1BR in each local offset control unit may be dispensed with and the connections AOC, 10C, OOC and FRC extended in common to similar relays in the master controller. Traffic signal controller, Fig. 7. Synchronous motor TM rotates a series of cams TCS, TCR, TCM, cam TCS being illustrative of one of a series of cams ordinarily provided for operating the traffic signals 1TS. The controller is shown in the rest position with the motor disconnected and the cam TCS near the end of the highway green signal period with positive A.C. power connected via cam contact TS-1 to signal 1TS. For operation on a fixed time or non traffic actuated basis SWF is closed. During the period of the time control cycle when earth is applied to lead 1PC by the local cycle offset control unit, a pulse of current flows through the motor setting the cam shaft into rotation. Contact TS-3 operated by cam TCM completes a driving circuit for the motor and the unit completes one cycle of operation stopping again in the rest position when contact TS-3 reopens. For operation on a traffic actuated basis, switch SWF is opened and the unit is merely permitted to come into operation during the period when earth appears on lead 1PC. If during, this period one of the traffic actuated contacts 1DS-1, 1DS-2 is closed relay 1RD in operating starts the motor via contacts 1vd-3 and holds itself over contact 1vd-5. Cam contact TS-3 provides the motor driving circuit, and cam TCR and contact TS-2 breaks the relay holding circuit. The unit therefore operates through one cycle and resets as before. Motor TM may be operate