Patent GB-1078283-A (GB)
Title: Improvements in and relating to traffic monitoring systems
IPC: G06G7/76
Filed: 1964-06-23
Abstract: 1,078,283. Road traffic measurements. GENERAL SIGNAL CORPORATION. June 23, 1964 [July 15, 1963], No. 25886/64. Heading G4Q. A traffic monitoring system for detecting congestion in the zone between two points comprises means for counting the number of vehicles entering the zone during a first time interval and means for subtracting from the count the number of vehicles leaving the zone during a second time interval, the time intervals being related to the distance between the points divided by the average speed of the vehicles. In Fig. 1, signals from vehicle detectors at each end of the zone are used in unit 13 to calculate average vehicle velocity which is integrated in unit 20 until the integrated value equals the voltage set on a distance control 23, which normally corresponds to the distance between the detectors. When the resultant input to comparator 21 changes sign, the comparator produces an output which is amplified and fed to energize relay R1. Contact 15 of R1 changes the sign of the input to integrator 20 which then integrates back to zero when it again activates the comparator 21 to de-energize R1. Thus R1 is alternately energized and de-energized for periods of time equal to the average time of travel of a vehicle between the detectors. The detectors 11 and 12 actuate respective negative and positive pulse generators 26 and 27 which feed counters 24 and 25 in one interval and counters 25 and 24 in the next interval, so that the counters indicate the difference between the numbers of vehicles entering and leaving the zone in successive intervals. At the end of each interval one of the relays R2 and R3 is operated momentarily to pass the output of its respective counter to an analogue memory 32 and to reset the counter. Memory 32 stores the difference count for each interval and its content is indicated by a meter 44; the content of the memory is also passed in a positive sense, if necessary through a sign changer 36, to a comparator 39 which produces an output to actuate a relay R4 and a utilization means 57 if the count exceeds a value set by unit 40. The unit 40 provides two preset voltages which are adjustable separately to determine the on and off levels of comparator 39. The utilization means may comprise an alarm or a recorder. The difference between the instantaneous pulses produced from the detectors is also calculated by the block 9 to activate the utilization means 57 if the difference between the volumes of traffic entering and leaving the zone exceeds a predetermined value. Average speed computer.-Relay R11, Fig. 3, is energized from detector 11 and remains energized for the whole time that a vehicle is sensed by the detector 11. An operational amplifier 110 is provided with a feedback capacitor 111 which receives a charge from capacitor 100, each time relay R11 is energized. Energization of relay R11 also provides a discharge path for capacitor 111 through resistance 107, and by equating the charging and discharging currents it is shown that the output voltage of the amplifier is proportional to the average speed. Relay R12 operated by detector 12 operates in a similar way, so that the output is proportional to the average speed at the two detectors. Reference has been directed by the Comptroller to Specification 967,666.