Patent GB-1063958-A (GB)
Title: Improvements in and relating to traffic monitoring or control systems
IPC: G06G7/76
Filed: 1964-06-23
Abstract: 1,063,958. Road traffic measurements. GENERAL SIGNAL CORPORATION. June 23, 1964 [July 3, 1963], No. 25887/64. Heading G4Q. A traffic monitoring or control system comprises means responsive to traffic flow in first and second directions to provide first and second electrical signals proportional to the magnitudes of the flows, and means for modifying one signal as a function of the other or of both signals to produce an output related to both signals. In Fig. 1 a plurality of vehicle detectors 10-13 are arranged along a traffic artery and each controls a relay, such as 1A, adapted to control the charging of a capacitor (15) through its contact (14). The detectors are preferably of the ultrasonic type and are adapted to actuate their associated relays as long as a vehicle remains in the detection zone. Thus the charge on capacitor 15 is proportional to the percentage detection time of detector 10, and this is shown to be similar to the percentage of road occupied by vehicles. Signals from the inbound traffic detectors are added in an operational amplifier 29 to provide an output signal -I  equal to the mean value, and similarly an output - O for outbound traffic is provided at terminal 26. In Fig. 2 the signal - O is reversed in sign by amplifier 34 and added to - I in amplifier 38 to produce a difference signal I-O which is averaged, for example, over 5 or 10 minutes, in unit 41 and passed to a level classifier 412 which operates relay R1 if I-O << zero and relay R2 if I-O >> zero. When relay R1 is operated lines L1 and L2 are energized positively and negatively respectively and cause the energization of a polarized relay R3 at a local controller. When R2 is operated the energization of L1 and L2 is reversed and relay R4 is operated. At the local controller a particular offset is selected according to whether R3 or R4 or neither is energized. In modifications, Figs. 3 and 4 (not shown), the signals - I and - O are processed by operational I#  amplifiers to produce values of - or of # O I + O which are used to control R1 and R2. In another arrangement, Fig. 5, the fraction I - is calculated without previously deriving I O and O. The inbound detector relays 1A-4A control the charging of feedback capacitor 98 of operational amplifier 98 whilst the outbound relays 18-48 control discharge resistances 103 -106. It is shown that this gives an output I proportional to -. In a modification, Fig. 6 O (not shown), the amplifier circuit is such as to I produce an output proportional to . This I + O circuit also includes a switch associated with each detector relay and adapted, when operated, to disconnect the relay from the circuit and to give extra statistical weight to similar (i.e. inbound or outbound) detectors by way of compensation. Each switch may be operable manually or may be operated automatically if the detector fails to detect a vehicle within a predetermined period. The period may be adjusted according to time of day by a clockcontrolled switch. In another modification, Fig. 7 (not shown), the amplifier circuit is I - O arranged to calculate # and in a further I + O modification, Fig. 8 (not shown), cross street detectors are included in the circuit which C calculates where C is the cross C + ¢(I + O) street flow. In a further arrangement, Fig. 9 (not shown), an amplifier is normally connected to calculate I + O #,but if this exceeds 5% relay circuits 2 operate so that the amplifier calculates the higher of I or O. The amplifier output passes to an averaging circuit and a level classifier controlling two relays which control a variablefrequency pulse generator and thereby control the length of a cycle. Further amplifier circuits C normally calculate and are modi- C + )(I + O) C C fled to calculate or if traffic is C+I C+O heavy and this output controls the offset.