Patent GB-535709-A (GB)
Title: Improvements in traffic control systems
IPC: G08G1/08
Filed: 1939-10-17
Abstract: 535,709. Road-signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PREIST, T. P., THOMPSON, G. W., and TAYLOR, J. H. Oct. 17, 1939, No. 28030. [Class 118 (ii)] In a system for use at a complex intersection where a large number of roads converge, such as the Bank intersection in the City of London, the lamps'associated with the various approaches are controlled by individual phase units which always tend to assume a normal condition in which red is shown to traffic approaching the complex and green to traffic leaving it. The phase units are associated with a common unit, which when controlled by a master controller in accordance with a progressive plan allots to each phase unit a period or periods in a time cycle during which right of way may be given to approaching traffic. The phase units at adjacent approaches, such as Threadneedle Street and Cornhill, may be interconnected to provide a "green overlap period " during which R.O.W. is given to both approaches, the extent of overlap being determined by the volume of waiting traffic on the halted approach. Moreover, should there be no traffic on an approach at the beginning of its plan green period, R.O.W. may pass to the adjacent approach if there is waiting traffic thereon, and the first approach loses its turn until the next time cycle. If no progressive plan is in operation, the common unit co-operates with the phase units to give R.O.W. to the approaches in accordance with the demands thereon. A manual control unit is provided, and this is combined with a "green interlock " arrangement which ensures that green is never shown simultaneously to conflicting approaches. Fig. 1 shows a plan of the Bank intersection, with phase lamps A ... G for approaching traffic and reverse phase lamps AV, CV, EV, F V for traffic leaving the complex. The general principle is to allow entry first by the east and west approaches in several stages and then by the north and south approaches. The phase units are of the camshaft type with neon tube timing, as described in Specification 403,732. Operation of common unit, Figs. 11-13, and phase unit A, Figs. 6, 7, under control of master controller. A cycle-dividing switch CD which is driven by impulses from the master controller has its banks 3, 4 and 5, 6 cross-connected to send start and stop impulses to determine the plan green period for each phase, the connections being varied according to which of three plan relays 1P-3P is operated. In the phase unit A, which is located at the Threadneedle Street approach and has reverse phase lamps AV relating to the Cornhill outlet, relay AP responds to the start impulse and connects up AX. If a demand already exists, AR is up, and a quick changing circuit is made for condenser QA to move the camshaft, from position 1. After timing of the amber and initial interval periods, the camshaft is maintained in position 4 as long as phase A traffic persists, condenser QA being shunted by repeated operation of AR, which does not lock in this position. It will be noted that a green arrow lamp is provided in parallel with the phase AV red lamp to allow filtration into Threadneedle Street. The stop impulse at the end of the plan green period short-circuits AX, and a quick charging circuit is again made for QA to advance the camshaft. After timing of the amber period, a minimum green period is given to the reverse phase AV before the camshaft goes to position 1, this being important under isolated working conditions. Relay AR energizes and locks as the camshaft moves from position 4 to register the continued demand on phase A. If traffic ceases during the plan green period, condenser QA charges over the switch AVS and R.O.W. is transferred either to phase AV as above or to the associated phase B as described later. In either case, phase A cannot regain R.O.W. until the next cycle since AP is back. Isolated working. If the plan selection circuit is opened, relay FT, Fig. 11, energizes over back contacts of plan relays 1P-3P and makes a charging circuit over adjusting switches TAS, UAS for condenser QB. After a short time, relay F operates and connects up ISZ which prepares a fresh charging circuit. When a demand occurs, the demand relay, e.g. AR, applies a marking to banks 3, 4 of the switch CD and connects up ST, whereupon the successive operations of F under the control of condenser QB step the switch to the marked position, in which AP operates to give R.O.W. to phase A. To avoid delay when no phase has R.O.W., however, a quick stepping circuit by interaction with MX is provided under the control of RZ which energizes over a chain circuit through all the phase units. This circuit depends also on a relay SQ (not shown) which operates in parallel with ST under the control of phase units C, F when the corresponding outlets (which are provided with reverse phase detectors FV1, 2) have been cleared. Isolated working may be initiated by relay AZ if the switch CD is out of synchronism with the impulses from the master controller. Relays X, UR may be provided to set up an all-red condition to approaching traffic when a change of plan occurs, relays AX &c. being disconnected. Phase unit B, Figs. 8-10, with green overlap arrangements. This is located at the Cornhill approach and may co-operate with phase unit A in conjunction with a traffic recorder to give a green overlap period. Relay BZ is then wired to banks 3, 4 of the switch CD and BP is connected direct to contact br3 for isolated working. Relay BZ is energized by a start impulse 20 sec. before the phase A stop impulse, connects up BX and makes a charging circuit for condenser QBA by way of overlap timing switch OTS, and the subsequent operation of BA results in phase B receiving R.O.W. Condenser QBA is pre-charged in accordance with the volume of waiting traffic ; if traffic is very heavy, QBA is already fully charged and BA operates at once, but if traffic is light, there is no initial charge and the full 20 sec. elapses before BA operates. The traffic recorder, Figs. 14, 15 (not shown), is started by a relay in parallel with the phase B red lamp and counts the number of vehicles passing over the detector VRD2 by means of condensers controlled by units and tens charging circuits. After a predetermined number of vehicles, e.g. 60, have been counted, the tens charging circuit is transferred to condenser QBA by relay VF (not shown). Should there be no traffic on phase B, the operation of BA at the end of the 20-seconds period connects up BSX, which is otherwise short-circuited by BR, to maintain the camshaft in position 1 and disconnect BZ. Any subsequent demand on phase B must wait until its plan green period in the next cycle. If phase A does not require R.O.W. for the whole of its plan green period, its camshaft remains in position 1 or steps to position 5, and a circuit is made over C13, Fig. 7, for relay BQ, Fig. 10, which simulates the operation of BP, and allows R.O.W. to pass to phase B ahead of plan should there be traffic thereon. Phase A cannot regain R.O.W. until the next cycle. A similar transfer between the north-south and east-west parts of the cycle may take place under light traffic conditions. Alternatively, a switch may be provided in the common unit to hunt for a calling phase and give it R.O.W. ahead of plan. Manual control and green interlock unit, Figs. 16, 17. A pairof relays RKA, RKB, each of which disconnects the other, are associated respectively with the phase units of the eastwest and north-south approaches, and prevent simultaneous lighting of the green lamps of conflicting approaches. For manual control, a switch FS which occupies position 2 or 3 for automatic working, is moved to position 5. Relays AX &c. release and set up an all-red condition, and AT, Fig. 11, energizes and connects up the demand relays AR &c. R.O.W. may now be given to one or more phases, subject to the interlock arrangement, by means of corresponding keys KMA &c. which connect up RKA or RKB followed by relays such as AP, AX in the appropriate phase units. Specification 515,860, [Group XL], also is referred to.