Patent GB-1022197-A (GB)
Title: Improvements in and relating to control systems for vehicle traffic signals
IPC: G08G1/081
Filed: 1963-10-14
Abstract: 1,022,197. Road traffic signals. GENERAL SIGNAL CORPORATION. Oct. 14, 1963 [Nov. 23, 1962], No. 40394/63. Headings G4H and G4Q. In a control system for controlling the cycle of a number of sets of traffic signals, timing signals from a central office are fed to local controllers, comprising counters, associated with each set of signals and means are provided to change the signal display when the associated counter reaches a predetermined count. The local controllers may be synchronized with the timing signals with different offsets, to give smooth flow along a main route, and the offset and cycle split may be set to one or other of two predetermined values from the central office to cater for traffic conditions at different times of day. The local control system is applied to a multiple junction, Fig. 4, in which the duration of the cross street B phase is modified in accordance with traffic demands registered by detectors in that street, and the system also provides that the B phase may be omitted if no demands have been registered. In the event of a failure of the control signals from the central office, the cycle may be controlled from a local dial unit. The central office equipment 10, Fig. 1, comprises a pulse generator 11 producing a train of 100 positive pulses followed by a negative synchronizing pulse which are fed over lines L1, L2 to the local controllers. The pulse repetition rate is adjustable by unit 12 to vary the cycle length. Additional lines L3, L4, C are also provided to enable a desired offset or cycle split to be selected by means of switches 15, 16, which control relays OS, SS. The positive timing pulses actuate relay PC to feed - pulses to step the counter 20 and the negative pulses actuate relay NC to feed further impulses to the counter via switch 22 or 23 depending on whether relay OS is actuated or not by the offset selector switch 15. The switches 22, 23 determine the value to which the counter 20 is reset at the end of the counting period. For example switch 22 may be so set that when relay OS is de-energized the counter is reset to count 25 at the negative synchronizing pulse. Pulses from relay PC are also used to control an Eccles-Jordan circuit 27 which steps a local counter 26. Normally counters 26, 20 step in synchronism but actuation of selector switch 15 to change the offset causes a sudden change in the phasing of the offset counter 20 relative to the synchronizing pulses resulting in a difference between the two counters since the counter 20 is now reset to a different value via offset switch 23. If counter 26 is ahead of counter 20 by ten to forty-nine counts relay R1 operates actuating relay S to slow down the counting rate of counter 26 by inhibiting one trigger pulse in ten from the output of the Eccles-Jordan circuit. When the difference is less than ten counts, relays R2 and R operate to stop counter 26 completely until counter 20 catches up. If counter 26 lags behind counter 20 from one to fifty counts relay F is actuated to provide an additional trigger pulse every ten pulses, thus speeding up the count of counter 26. The offset of the local counter 26 is thus changed gradually in response to a sudden change in the offset counter 20. Whenever counter 26 reaches zero count relay OR is actuated to denote the beginning of a signal cycle at that location. The cycle split is determined by the point in the counting cycle at which relay SR is actuated, that is, the system operates in one phase with SR released, and in another with SR actuated. If relay SS is released relay SR may be actuated at, say, the count of 60 by switch 43. If on the other hand relay SS is actuated by switch 16, then relay SR may be actuated at, say, the count of 72 by switch 42. If more than two phases are required other SR relays may be included, operating at different points in the timing cycle, each associated with its own split switches 42, 43. In order to ensure that the change in split is only initiated at the commencement of a cycle, the actual change is initiated by a relay S, Fig. 2F (not shown), which can only operate when the local counter reaches 00, even though the split selector relay SS may change its condition at any time in the cycle. In a modification, the cycle offset and split command signals are transmitted over the lines L1, L2 instead of over separate lines L3, L4, C by transmitting a number of negative pulse (up to 89) interposed between the positive pulses, instead of only a single negative synchronizing pulse. With such a system, for example, the tens digits from 0-8 might represent one of nine different offsets, the units digits from 1-5 might represent one of four cycle splits, and the other unit digits might represent some other command signals, such as an emergency green along the main artery, flashing lights, or maximum speed signals. In the modified system, the central office equipment, Fig. 8, includes a trigger pulse generator 300 which feeds signals to the positive pulse former 302 and the negative pulse former 312, the latter signal being delayed so that the positive and negative pulses are interposed. A third output from the generator 300 steps a counter 304 which is arranged to switch flip-flop 311 to its " 1 " state at the start of a count, and back to its " 0  state when the required number of negative pulses have been counted. The flip-flops 311 gates the output of the negative pulse former to feed the required negative pulses to the lines L1, L2 interposed between the hundred positive pulses. A maximum of 89 negative pulses is used so that the start of the negative pulse train may be determined. The pulse train is received by the local equipment, Fig. 9, and relay NC responds to the negative pulses to feed them to a counter 322. In this unit, the counter 333 counts the tens digits and actuates a relay F0 . . . F9 depending on the count. The first pulse of the negative train also provides a synchronizing signal and is fed, via contacts on whichever of the relays F0 . . . F9 is actuated, to the offset counter 20 to provide the required predetermined offset. The units digits are counted in counter 324, and the count stored in memory 331 until the commencement of a local timing cycle of counter 26 when a signal is fed, via contacts on the actuated one of the relays S1 . . . S0 to actuate the cycle split relays SR1, SR1 giving the required split between A, B and C phases or to initiate one of the special functions. Circuit details of the local controller circuits are given, Figs. 2A-2H and Fig. 10A-10D (not shown).