GB1027880A - Improvements in and relating to road traffic control - Google Patents

Abstract

1,027,880. Road traffic measurements. E. J. SCHEPERS. Nov. 20, 1964 [Nov. 21, 1963; April 16, 1964], No. 47399/64. Heading G4Q. In a system for indicating traffic stoppages in a road section having at least two mutually accessible lanes with the same traffic direction, for example, in a tunnel, the ratio of traffic volume in the left lane to traffic volume in the right line normally decreases from a high value at low total traffic volumes to unity at high total traffic volumes; if there is an obstruction in either lane the ratio will alter markedly from its normal value, and this alteration is detected and used to operate an alarm. Referring to Fig. 2 detectors 4 and 5 are placed in respective traffic lanes 2 and 3 and feed amplifiers 6 and 7. The outputs of the detectors at the beginning of the road section pass through OR gate 10 to a classifier circuit 11 which produces an output on one of the lines 12-15 according to the level of the total volume. The outputs of each pair of detectors pass to a comparator circuit 16 which compares the ratio of the traffic volumes with limits selected by the inputs on lines 12- 15 and produces an alarm output on line 17 if these limits are exceeded. At the lowest level of traffic volume when line 12 is energized, there is no upper limit to the ratio and the system responds to a difference in the number of vehicles entering and leaving a section between two pairs of detectors. When a gate 10 has not been actuated for a period, e.g. 10 seconds, equal to the maximum time assumed for a vehicle to pass between two pairs of detectors, a comparator 21 compares the counts in counters 19 and 20 and passes a signal to unit 22 if there is any difference in the counts. The signal from unit 22 inhibits the unit 22 of the succeeding section via lead 23 and is inhibited by an output from the succeeding comparator via lead 24. This prevents a false alarm caused by a false count which might be caused by a vehicle actuating a pair of detectors 4 and 5 simultaneously. An alarm signal passes through gate 25 if one comparator 21 but not the two adjacent comparators gives a difference signal and if line 12 is energized, i.e. there is minimum traffic flow. The detectors 4 and 5 may be of the capacitive type influenced by vehicle axles. The inputs to the counters may include coincidence detector circuits, Figs. 6 and 7 (not shown), so that a single coincident detection by both detectors of a pair generates an additional count unless followed within a short time by a second coincidence. In this way two vehicles passing over the detectors simultaneously are counted but a single vehicle passing over both detectors is only counted once as the signal due to its second axle cancels the additional count.