Patent GB-475118-A (GB)
Title: Improvements in or relating to traffic control systems
IPC: G08G1/08
Filed: 1936-05-13
Abstract: 475,118. Road-signals for controlling traffic. AUTOMATIC ELECTRIC CO., Ltd., (in Liquidation), PREIST, T. P., and THOMPSON, G. W. May 13, 1936, No. 13598. [Class 118 (ii)] The apparatus for a road-traffic control system comprises a common control unit which is associated successively with equipment individual to the various sets of signals, the individual equipments being arranged as readily removable units and any number of units being operable from a single control unit without change. The common unit includes two oilimmersed uniselectors, one of which selects the particular set of signals to be controlled and the other controls the signal cycle. An allred period may be provided, the apparatus for this and for any other special facility being supplied as a further jack-in unit and a road pad being provided between the sets of signals to enable the all-red period to be extended by traffic in the crossing. A single timer times the initial, vehicle, amber and all-red periods for all sets of signals. In the Figures, the apparatus for a single set of signals is shown in the upper part of the diagram and is associated with bank contacts 1 of the finder switch F. If the apparatus is switched on with the switches as shown, magnet DDM operates and relays DS and DSX pull up. Relay DS opens the magnet circuit and wipers D move to contacts 2. It is assumed that the all-red switches ARS &c. are all in the off position so that contacts AAR, BAR, &c. are closed. Relay PA is operated over wipers F2 and D2 and relays GA and RA are energized to light the phase A green lamp GA. Relays VE and ARC are pulled up and condenser QA is charged over switch AVS. Each vehicle on phase A energizes relay DA to shunt condenser QA. A vehicle on another phase, say phase C, operates relay DC (not shown) and locks in series with relay ST. Relay ST completes circuits for IS, for relay A and for charging condenser QB of the maximum timer. If there is no phase A, traffic condenser QA is fully charged and relay A energizes at once. Relay PAR is energized to give the amber signal to phase A and switch D is stepped to position 3. Relay DSX discharges condensers QA and QB. Relay VE releases. Relay IS is slow to operate and its circuit is opened under these conditions before it pulls up to give no initial interval to phase C as the vehicle thereon will not have to stop. If condenser QA is not fully charged so that relay A is not operated at once, relay IS has time to pull up and gives the initial interval. The amber period is timed by condenser QA charging over AAS and the finder switch magnet FDM is operated and interacts with relay FS until its wipers rest on the contacts of the calling phase C. The relay AC (not shown) of the calling C phase is energized over wiper F1 to light the amber lights on' phase C. When relay A energizes at the end of the amber period, switch D is stopped to position 4 and magnet DDM interacts with relay DS to step the switch to position 1. In this position, if relay IS is up, an initial interval is timed by condenser QA charging over C18 (not shown) and then the switch D steps to position 2 where the apparatus waits for a call from another phase. If, however, traffic is flowing on the A phase, relay A does not operate immediately, relay ST pulls up and the condenser QB commences to charge over the phase A maximum timing switch AMS. Relay B energizes at the termination of the period and effects the change of right of way as described for relay A above, but relay DA is locked up to ensure the ultimate return of right of way to the A phase. In addition, relay IS is operated to give an initial interval to the C phase whilst the amber period is extended by the insertion of resistance 14 in the charging circuit of condenser QA. If an all-red period is required for any phase, the relative timing switch ARS is turned to an appropriate position. The off-normal contacts AAR open. Under these conditions relay ARC is not operated with the switch D in position 2 and when switch D moves to position 3 switch F does not hunt for the calling phase. The amber period is timed as described above and switch D moves to position 4 where an all-red period is timed over ARS, the amber signal on phase A being released when switch D leaves position 3. A pad may be provided in the crossing as at ARET which, when operated, energizes relay AR to discharge condenser QA and extend the all-red period. This is of particular use when the all-red feature is used for clearing a bottle neck. When relay A energizes, switch D is stepped to position 5, switch F hunts for the calling phase, the red-amber signal is lit on this phase and is timed by' resistance 15. The switch D then moves to position 1 and the cycle recommences. The all-red period may be suppressed if no traffic is flowing on a phase. For this purpose a suppressor switch ARSS is provided arranged so that if no traffic flows on the phase having right of way (say phase A), condenser QB is charged over ARSS. Relay C operates and relay ARC energizes, the relays releasing if a further vehicle operates the pad on phase A and the charging recommencing. If relay C is up when another phase calls, relay ARC is held over wiper D4 in position 3 so that switch F hunts for the calling phase and switch D is stepped through positions 4 and 5 to position 1 as described above for the system with the all-red switch off. The neon tube timers may be replaced by valve timers as described in Specification 428,544.