Patent GB-1189831-A (GB)
Title: Method and Apparatus for controlling Traffic Flow in accordance with Traffic Presence
IPC: G08G1/08
Filed: 1967-06-05
Abstract: 1,189,831. Traffic signal control. E. W. BLISS CO. 5 June, 1967 [6 July, 1966], No. 25768/67. Heading G4Q. Traffic signals at an intersection of two traffic phases are controlled by monitoring a particular area in the path of each phase, developing presence signals as long as traffic is present in the respective areas and using the presence signals to control the traffic signals; if only one presence signal occurs the traffic signals change immediately, but if both presence signals occur simultaneously, the traffic signals change after a delay. Fig. 3 is a block diagram of a local controller energized by presence detectors D1/D2 in the phase A approaches, D3/D4 in the phase B approaches and D5 in the intersection area (Fig. 1, not shown). The detectors may be underground loops or overhead ultrasonic detectors. The operation is controlled by a binary counter BC feeding a binary-to-decimal converter BDC to produce signals successively on lines 1-6 each time an input is applied to the counter. Initially a signal is present on line 1 and this goes via multiplier (distributer) 10 to energize the phase A " go " signal 12A. If a vehicle is detected by phase B detector D3 or D4 while no vehicle is present in the area of phase A detectors D1, D2, a signal is passed from generator 18B through AND circuit 16 (on the lefthand side of the Figure) to the y input of NOT circuit 22. This is not overridden by an x signal from generator 18A so pulse circuit 24 steps the counter BC to energize line 2 and de-energize line 1. The phase A " go " signal 12A is now replaced by a " caution " signal 28A operated through multiplier distributer 26, which also starts a timer 30. After a certain interval this passes another signal to the counter BC to step the output to line 3. This extinguishes the phase A caution signal 28A and energizes an all-red signal 34 through multiplier 32. When the intersection presence detector D5 indicates that no vehicle is in the intersection the overriding x input of NOT circuit 36 is removed and pulse circuit 40 steps the counter BC to change the output to line 4. The phase B " go " signal 12B is now energized and the same operations proceed for phase B using the circuits on the right-hand side of the Figure. If a vehicle is sensed by both phase A and phase B detectors simultaneously the phase showing a " go " signal is not terminated immediately since an x input is present on NOT circuit 22. Instead, AND circuit 14 is energized to start a timer 20 and the existing phase continues to have the right of way until this timer steps the counter BC. In a modification (Figs. 4, 6, not shown) the intersection presence detector is split into four, one for each quarter of the intersection, and the outputs of these are fed through OR circuits to the NOT circuits 36. Also, the " caution " signals 28 are controlled by these detectors instead of by timers 30. The outputs of both pairs of diagonally opposite detectors are combined in OR circuits (44), the outputs of which control the " caution " signals through AND circuits from lines 2 and 4 and also provide overriding x inputs to NOT circuits controlling the change from line 2 to 3 or 5 to 6.