Patent GB-418070-A (GB)
Title: Improvements in or relating to traffic control systems
IPC: G08G1/08
Filed: 1933-04-18
Abstract: 418,070. Road-traffic control systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, RENSHAW, A. P. B., Brookwood, Alder Road, West Derby, and WRIGHT, D., 91, Hampstead Road, Elm Vale, all in Liverpool. April 18, 1933, No. 11377. [Class 118 (ii).] In a traffic control system, traffic flow from one of a number of roads meeting at a junction is permitted for only a portion of the time that traffic flow from another road is permitted. The invention is particularly applicable at a T- junction of a main road (regarded as two roads) and a side road. The traffic phases comprise (1) flow from the two main roads simultaneously ; (2) flow from one main road turning right, across the other main road traffic, into the side road; simultaneously with flow from the first main road into the other; (3) flow from the side road only. In the plan shown in Fig. 5, an additional road pad C is provided for main road traffic turning right into the side road. The green lights of the A.C. set permit right turning traffic flow, but these green lights are also lit for simultaneous flow from the two main roads, the volume of traffic from left to right forming a definite bar to right turning traffic. If this were undesirable, separate signals would be provided for the right turning traffic. The system may be regarded as a modification of the three-phase system described in Specification 409,376, the timing apparatus being similar to that described in Specification 403,732. Road pads as described in Specification 360,924 may be used. The system may be included in a flexible progressive system and provision is made for omitting non-calling phases from a cycle, for hold-ups for pedestrians, and for dealing with faults. Right of way remains with the phase last in action if there is no other call, but it may be caused to revert always to a particular phase. Operation. It will be assumed that the main roads have the right-of-way at present, green lamps A, AC being lit and the right-of-way to phase C being ineffective owing to phase A traffic. Sequence switch C1-C22 controlled by solenoid S, Fig. 2, is in the second position in which the cam springs are operated as shown in the table, Fig. 4 (M= closed). The circuits of the road pads (phases A to C) are shown in Fig. 2, and those of the lamps (GA, GAC &c.) in Fig. 3. Various operations are timed by charging condensers QA-QC until neon lamps FA-FC strike and the timing is adjusted by hand controlled switches VH(A-C) C.AMB, IN(A-C), associated with tapped resistance XA, and MAX(A-C) associated with tapped resistance XB. Alternating current for the lamps and relays and direct current for condenser changing is derived from the mains as indicated in the key at the foot of Fig. 1. Assuming that A traffic ceases and B traffic arrives, relay E operates over pad B, locks up and energizes H, Fig. 4, which locks up to prepare the amber lights AA, AAC, AB. Since K, Fig. 4, has been previously operated by the A pad, which energizes relays D and G, a charging circuit for QA exists over phase A vehicle-interval switch VHA. As no A traffic has arrived to short-circuit condenser QA over d2 and C15, the voltage builds up unil neon lamp FA strikes to operate A over e2 so that solenoid S steps the sequence switch to 3, condenser QA being discharged by a contact of S. All the amber lamps are now lit and green lamps GA, GAC extinguished, red-amber being presented to phase B. Condenser QA is now charged over the common amber timing switch C.AMB and after an interval A again pulls up to step the sequence switch to 4 wherein L pulls up, lights green lamps GB, extinguishes RB and lights red lamps RAC, and amber lights being extinguished directly by the movement of the sequence switch. Relays G, K fall back and red lamps RA light up. Condenser QA is again charged over the initial interval timing switch INB and the sequence switch in due course steps to 5 without changing the lamps. QA again changes up but the discharge circuit for operating A over C6 is now open so that it cannot pull up unless phase A or C calls and operates D or F. Further calls from phase B operate E (which is now unlocked at C17) to short-circuit the condenser over C15 so that the right-of-way for phase B is extended proportionally to the speed of the vehicle since the period of operation of E depends on the speed. The maximum time control now comes into operation if there is a call from phases A or C. Condenser QB becomes charged over switch MAX.B and contacts of phase relays D or F, and FB strikes to operate B which energizes S to step the sequence switch to 6. Assuming a call from C, right-of-way is then transferred to C in a similar manner to the transfer from A to B. Relay B also brings up the road relay E to simulate a call from phase B so that, in due course, the right-of-way forcibly removed from phase B is restored to release the B traffic which had passed the pad at the time of forced removal (there might not be a call from B subsequently). Similarly if the right-of-way for B is removed owing to a gap, B traffic crossing the pad during the amber interval operates and locks E. Under both of the foregoing conditions, the amber interval is extended by cutting in additional resistance YF into the amber timing circuit. During the change from B to C, which also permits right-to-left traffic on the main road, the amber signal is not given to the left to right traffic which is to remain stationary. Transfer from A to C jumping B which has no waiting traffic. Starting again with sequence switch in 2, the phase C pad operates F which locks up and prepares the circuit of relay A. Subsequently due to a gap in the A traffic or the maximum timing control, the sequence switch is stepped to 3 as will be understood from the previous paragraph. As there is no B traffic, H remains inert and the amber signal is given to phase A only. This means that the left to right A-traffic is warned but not the right to left. After the expiration of the amber period the sequence switch steps to 4 where G and K fall back and light red lamps RA. As however, there is no B-traffic (L normal) red lamps RB remain alight, RAC remain extinguished and a rapid charging circuit for QA is completed over C16 and low resistance YH. The sequence switch steps quickly to 7 where M pulls up to stop the switch, relay J being operated in position 5. The right of way is now to traffic C and right-to-left traffic A. Inclusion of the system in a flexible progressive system. The maximum timing circuit is open at C18 during the A vehicle interval period so that when the maximum period elapses the signals remain unaltered until C18 is short circuited by a relay responsive to signals from the master timer as described in Specification 403,720. Dealing with faulty apparatus ; interval for pedestrians during continuous flow on one phase. If the sequence switch is not stepped on due to faulty pads &c. or to continuous traffic over A and no other traffic, the timing arrangement shown in Fig. 4 comes into operation after a time considerably longer than the maximum limit to simulate a call on all phases. Normally condenser QC is being continually shorted by contacts of solenoid S but if this does not occur QC charges up over a manually adjusted switch PDC, and FC strikes to operate PC which completes circuits for all the road relays D-F.