GB1129498A - Traffic actuated control system - Google Patents

Abstract

1,129,498. Road traffic signals. LABORATORY FOR ELECTRONICS Inc. 19 Oct., 1966 [1 Nov., 1965], No. 46763/66. Heading G4Q. A road traffic signal controller of the type described in Specification 1,063,048 is provided with a timing circuit 55, Fig. 1, adapted to be started when a vehicle is detected on the route not having right-of-way, and a second timing circuit 24 which is reset each time a vehicle is detected on the route having right-of-way, the combined outputs of the two timers being fed to a trigger circuit 50 adapted to initiate a change of phase. The timing circuit 55 comprises a capacitor (170, Fig. 2, not shown) shunted by a transistor (120); when the transistor is cut off in response to a vehicle demand supplied at input terminal 20 or 23, the capacitor charges and the potential across it is fed through an impedance converter 44 to resistance 42. The timing circuit 24 is similar and is re-set each time a vehicle is detected on the route having right-ofway, either gate 31 or gate 32 being open due to a signal AV or BV derived from an electronic counter (not shown) controlling the cycle. The potential at the output of the timer 24 is therefore proportional to the gap between vehicles and is fed to resistance 40. The potential at point 46 is the average of the outputs of the two timing circuits, so that the longer the waiting time the shorter is the gap between vehicles allowable before the trigger 50 fires. When this happens a bi-stable 35 is set and blocks gate 30; this prevents a third timing circuit (AT, Fig. 3, not shown) from being re-set by an output at terminal 262, and this timer accordingly times out and then switches the electronic counter to its next stage, thereby changing the phase. A maximum timer circuit (BT, Fig. 3, not shown) is started at the beginning of each right-of-way interval and limits the total right-of-way period; vehicle calls which are too late to prolong rightof-way are stored as a demand for change of right-of-way. The timer 24 uses a single charging resistance (144, 145, Fig. 2, not shown) which is adjustable but times in the same way for both routes; the timer 55 has different adjustable timing resistances for the two routes (Fig. 4, not shown) and its output is never sufficient to fire the trigger 50 in the absence of an output from timer 24.