GB503798A - Improvements in or relating to traffic control systems - Google Patents

Abstract

503,798. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PRIEST, T. P., THOMPSON, G. W., and TAYLOR, J. H. Oct. 19, 1937, No. 28511. [Class 118 (ii)] In a progressive-type traffic-control system wherein the signals at a number of related intersections are operated under the control of a master timer, the cycle time of the master timer is adapted to be varied in accordance with the traffic flow during right of way periods occurring in' different parts of the cycle at a plurality of key intersections. The system is described in connection with a circus, around which traffic proceeds in one direction; the cycle time being varied in accordance with the traffic flow on certain of the roads giving access to the circus. Controllers of the type described in Specification 403,732 are employed at the junctions of the incoming roads and the circus, it being convenient to employ 3-phase controllers at some junctions to control two such roads. With light traffic, the controllers operate independently, but with heavy traffic a main switch ATS is closed manually or by a time switch to convert the system to progressive working, two plans of different duration being available according to whether the flow is medium or heavy. Considering the operation of the signals at the first junction only, relay AT will operate, causing all the road relays to operate, thus simulating a permanent demand on all phases. A circuit may also be completed over wires 24, 25 to bring in an extra phase. The master timer comprises a switch DD stepped under the control of a timing circuit consisting of the resistance VR, neon tube FA and condenser QA. The switch releases the relays X, Y in turn to complete the maximum timing circuits for the two main phases, the maximum periods being variable in accordance with the traffic flow in the particular road in a manner similar to that described in Specification 488,796. Relays MTC are connected across the green signal lamps at the key intersection so that should the right of way leave the road before the maximum time to which the variable maximum period may be extended, due to the traffic being relatively light, the relay is operated, causing the switch DD to be quickstepped to the end of the strapped contacts, as relay H is operated and shorts out part of resistance VR, the duration of the master cycle being shortened when the right of way leaves the main phase earlier than according to the plan, at any of the junctions having a MTC relay. Faults. If the stepping switch DD fails, the other switch controlling the alternative plan is brought into service. A changeover of the plans is not permitted if the second switch is faulty. If one of the control pulses does not reach the slave controller, it reverts to isolated working at the end of the cycle. Normally when line 26 is earthed at the end of the cycle, relays XS, YS being unoperated, RS operates, followed by XS and YS. As switch DD steps on, relays XS, YS will be released when the corresponding pulse is received. If the pulse releasing X is not received, at the end of the cycle FS locks up operating an alarm and restoring over lines 10... 15 maximum periods suitable for isolated working and removing the permanent calls, by operation of contact fs4. When the lost pulse is sent, the controller returns to the progressive working.