GB1009445A - Improvements in or relating to road traffic signalling systems - Google Patents

Abstract

1,009,445. Road traffic signalling systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Feb. 22, 1962 [March 7, 1961], No. 8230/61. Heading G4Q. A road traffic signalling system includes provision for detecting the formation of a queue at a traffic-light controlled-junction and for varying the " green period " of the lights and preventing the entrance of further traffic from side roads into the main road in dependence on the length of the queue. Detectors AN, AS, BE, BW, Fig. 2, are the usual traffic detectors and they control the usual signals ANS1, ANS2, ASS1, ASS2, BES1, BES2, BWS1, BWS2. Additional detectors AB1, AC1 are provided for north-bound traffic, detectors AN, AB1 measuring the length of the queue existing at the beginning of a green period on phase A, while detector AC1 determines when the queue length is such as to cause saturation of the phase. The operation is based on the fact that if a queue has formed, traffic will travel over the first detector, and possibly the second, depending on the queue length, at a very low speed, say 5 m.p.h. The detectors AN, AB1, AC1 are shown in Fig. 3. At the beginning of the green phase a start signal ST is applied to gate IG and connects detector AN to a speed discriminator SD (set for speeds of 5 m.p.h. or less) for a time of at least 5 seconds determined by a timer in I.G. Operation of the detector by a slow moving vehicle (less than 5 m.p.h.) indicating that a queue has formed will trigger SD and a register A, the output from which (1) provides a signal to gate COA to disconnect SD from AN and connect SD to detector AB1 via COB, COA; (2) provides a path between SD and register B via A; (3) provides a reset signal to IG over RS2; (4) provides a signal to controller CON to increase the maximum " green " period from a low to a medium value. The reset signal to gate IG maintains the detectors energized for a further period and if a queue has formed beyond AB1, a vehicle travelling slowly over AB1 will similarly cause an output from register B which (1) disconnects detector AB1 and connects detector AC1 to SD; (2) completes a path between SD and register C via A, B; (3) provides a reset signal to IG over RS 2 ; (4) provides a signal to the controller CON to increase the maximum green period from a " medium " to a " high " value. The detectors AN, AB1, AC1 will still be energized over IG. If the queue extends beyond AC1, the first vehicle over AC1 will be moving very slowly thereby triggering SD, the consequential output from register C causing controller CON to transmit a signal to any adjacent controlled side rods to reduce the traffic flow from these roads by shortening the " green " periods in their directions and lighting indicators, e.g. " No left turn ", or divert the traffic into an alternative route. If no vehicle passes over a detector to operate SD while IG is open then IG will close and de-energize the detectors for the rest of the " green " period. Detectors responding to the presence rather than the passage of a vehicle may alternatively be used.