Patent GB-488796-A (GB)
Title: Improvements in or relating to traffic control systems
IPC: G08G1/08
Filed: 1937-01-13
Abstract: 488,796. Road-signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, J. H., THOMPSON, G. W., and RENSHAW, A. P. B. Jan. 13, 1937, No. 1058. [Class 118 (ii)] In a progressive-type traffic-control system wherein a number of controllers located at adjacent intersections on a main road are regulated in a certain phase relationship by a master timer, the master timer is controlled in accordance with the density of the traffic at a key intersection during each right-ofway period. The system facilitates related and continuous flow throughout an area including a number of converging streets having side turnings and employs controllers of the 4-phase (traffic phases A, B, C, D) and 3-phase types according to the nature of the intersections. The master timer is subjected to variable control in accordance with the traffic at an intersection where it is assumed that the density of the traffic flow is representative of the flow throughout the area. Normally with dense traffic in both lanes at the key intersection the master timer remains in step with the key controller and the rights-of-way are given to both lanes in turn as determined by the maximum period of the controller. If however the density in either lane falls, the maximum period is reduced and the right-ofway is transferred earlier than according to plan. In this event the master timer lags behind the key controller but this lag is compensated by the completion of a circuit between the key controller and the timer to speed up the latter until the correct point in the cycle is reached. The controllers are of the well known type comprising a step-by-step cam switch operated under the control of a condenser-gas discharge tube combination consisting of an A timer for extending the right of way in response to traffic flow, a B timer for preventing one road holding the right-of-way indefinitely if traffic is waiting on the cross-road and a C timer for timing the intervals between successive road-pad operations on the road holding the right-of-way so that the maximum period of the B timer may be varied in dependence on the traffic density. The controllers are operated in such a manner that the A timer is not operated to effect a change of signals until a break occurs in the cross traffic, and a call is received from the halted road. Since also the controller functions as part of a progressive system the operation of the maximum timer B is not immediately initiated by a vehicle on a halted road, but a circuit is prepared and subsequently operated upon receipt of a pulse from the master timer. At the key intersection a 4-phase controller, the sequence of which is A traffic phase signals ; all red ; C-traffic phase signals; all red, is provided and effects the control of the master timer in the manner shown in Fig. 9. The master timer comprises a switch D stepped under the control of an impulse combination comprising relay A, neon lamp FA and condenser QA, the impulsing rate being determined by the setting of a variable resistance. The switch effects the successive release of the X relays at controllers located at the various intersections for initiating the maximum timing on one phase of traffic followed by the successive release of the Y relays for starting up the maximum timing on another phase. In order that the speed of the master timer may be related to the density of the traffic at the key intersection, relays RGA, RGC are connected in parallel with the green lamps of the two phases and affect the master timer throughout these periods of the two phases. The bank D3 of the timer D has strapped contacts so that should the density on a phase at the key intersection become light and the right-ofway transferred earlier than according to plan one or other of the relays RGA, RGC will complete a circuit for relay H which shortcircuits part of the control resistance and speeds up the master timer through the remainder of the existing cycle. Various intermediate phases may be catered for in the bank contacts of the switch D between the master timer controlled phase periods. The relays AT may be operated manually or by a time switch during dense traffic conditions and serve to set up a permanent call on all phases and ensure that the system works rigidly to plan without placing reliance on the persistence of traffic. The repeat impulsing system described in Specification 446,288 may be employed so that calls may be repeated over linking leads from one controller to the next, the road detectors being rendered inoperative. Provision also is made for ensuring that right-ofway returns to a phase without any further detector operation in case vehicles have been stopped between the detector and the signals. Combined phase signals, i.e. the combination of one or other phases A, C with an intermediate phase B, may be operated by an arrangement wherein relays for operating the combined phase signals are connected in parallel with the red and amber lamps respectively of the one or other phase. The intermediate phase B may be completely eliminated when traffic conditions are known to be light by a local time switch or the relay AT at the master controller which facilitates quick-stepping of the cam contacts through the intermediate phase. Phase C of a 4-phase controller may be allocated to pedestrians.