Patent GB-1171832-A (GB)
Title: An Arrangement for Measuring the Density of Automobile Traffic
IPC: A47H5/03
Filed: 1967-02-09
Abstract: 1,171,832. Road traffic measurements and signals. COMPAGNIE GENERALE D'AUTOMATISME. 9 Feb., 1967 [9 Feb., 1966], No. 6347/67. Heading G4Q. In an arrangement for the control of a signalling system indicating the movement of automobile traffic on a highway having a plurality of local detecting systems located along the highway each system includes a detector 3 responsive to the passage of a vehicle to emit a signal which is fed to a ring counter 4 which counts a selected number n of vehicles, an electronic clock 5 which is started when the counter indicates one, the counter being zeroed, when the nth vehicle has been detected or by a signal from the clock, after a given time T 2  has passed, a device for measuring a quantity # proportional to the sum of the speeds of successive vehicles or a quantity S proportional to the sum of the reciprocals of the speeds and a memory 7 collecting the value of # or S when n vehicles have been counted or when a time T 2  has elapsed. The outputs from the clock and memory are fed to a comparator (10, Fig. 5, not shown), which compares the values # or S and the transit time T of the vehicles with a series of prerecorded values of # or S and T and from the relationships between them supplies control signals to the signalling system. The arrangement may be used to indicate the flow of traffic, e.g. along a motorway at a control centre or for the motorists themselves, e.g. indicating a traffic jam or accident. As shown the passage of vehicles is detected by an inductive loop 3 and is counted by ring counter 4. The speed of the vehicles is detected by radar 1 feeding a frequency meter 2 and the sum of the speeds is stored in the memory 7. With the total number of vehicles n to which the counter is set being counted before time T 2  has elapsed the sum of the speeds # and transit time are compared with prerecorded values in the comparator and according to their relationships fixed or flashing green, orange, or red traffic lights are energized indicating that the traffic is freely flowing to stopped respectively. If the selected number n of vehicles has not passed the detector 3 before the time T 2  has elapsed then since the pre-recorded values of # and T are for the selected number n the output from the frequency meter 2 is passed to a divider which divides the sum of the speeds by the number m of vehicles which have passed in the time T 2  and then to a multiplier of value n to correct the signal before passing it to the comparator. In an alternative detecting system (Fig. 6) the radar and frequency meter 1 and 2 are replaced by two detector loops 101, 102 in the road which control relays 103, 104 opening a gate circuit so as to allow the output from a signal generator 105 to pass to a totalizing counter 107 for the time of passage of a vehicle between the loops. The output from the totalizing counter is fed to a memory 108 and the second loop 102 detects the number of vehicles which pass and is counted by the ring counter as before. In this arrangement the quantity measured by the totalizing counter 107 is proportional to the sum of the reciprocals of the speeds. The detectors may be tuned circuit capacitative, magnetic, optical, infra-red, ultrasonic detec. tors, or radar or road contact devices can be used.