Patent GB-512439-A (GB)
Title: Improvements in or relating to traffic control systems
IPC: G08G1/08
Filed: 1938-03-03
Abstract: 512,439. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and THOMPSON, G. W. March 3, 1938, No. 6722. [Class 118 (ii)] In a vehicle-actuated system employing a camshaft rotated step-by-step by an electromagnet to effect the circuit changes for controlling the signals, the camshaft occupies the same position to give the corresponding signals to the various phases, the phase to which they apply at any time being determined by relays operated under the control of the traffic detectors. The system is described as applied to a five-phase controller, the camshaft having three positions corresponding to the initial, vehicle extension and amber periods, the position in which the spring contacts are closed being indicated by numerals. Provision is made for phase-overlap, the signals for the combined phases being operated from the equipment associated with the individual phases. Other camshaft positions may be provided for all-red and displaceable amber periods. Operation.-It is assumed that the camshaft is in the vehicle extension position 2, and that right of way (r.o.w.) is on phase A. Upon a vehicle approaching on phase C, relay CR locks up. followed by relays ST and 'CP, relays AS and ASR having been locked up in position 1. ST completes circuits for the vehicle interval and maximum green timers including relays A and B respectively. Traffic on phase A is able to obtain extension of r.o.w. by operating relay EX causing condenser QA to discharge partly. Upon either of the timers operating, the camshaft is stepped on to position 3 to change the signals, the amber period being timed by the A timer, at the termination of which the camshaft is stepped on to position 1. AS and ASR now release followed by R which causes relays CS and CSR to lock up. The initial interval is timed by timer A; after which the camshaft is stepped on to position 2 where relays CR, CP and ST release. Calls from two or more phases.-If r.o.w. is on phase C and a call is made from phase B, relay BP operates in position 2 of the camshaft. If now a call is made from phase A, relay AP operates and releases BP so that r.o.w. passes in cyclic order to the other phases which have called for it. Phase overlap.-In, order to provide for the overlap of phases D, E having a common lantern, the equipment of Fig. 5 is provided. With r.o.w. on phase D, relay OG is operated. If r.o.w. is to pass to phase E, relay EP will be operated and will maintain OG operated and prevent relay OA from operating through the normal amber period so that r.o.w. is maintained during the transition from phase D to E. If r.o.w. is to pass to another phase neither of relays DP, EP will be operated and OG will release and OA operate to give the amber-leaving and red signal. An extra r.o.w. period may be given to the combined DE phase by arranging an extra relay in each of the groups AP-EP and AS-ES operated by O.G. Manual operation.-Upon a changeover switch (not shown) being operated, a permanent call is put on each phase and the vehicle interval and maximum timing circuits opened. Operation of a push-button now causes magnet SOL to step. Specification 403,732 is referred to.