GB1348895A - Vehicle interval detection and signalling system - Google Patents

Abstract

1348895 Road traffic measurements A N MARSHALL 19 March 1971 7327/71 Heading G4Q A system for detecting when the time interval between successive vehicles travelling along a roadway is less than a predetermined value comprises a vehicle detector which signals the departure of a vehicle from a point and generates a timing signal for the predetermined time; if the arrival of another vehicle at the point is signalled during this time, a warning is displayed to the driver, the police are notified, and/or a photograph is taken. In a system employing solenoid switching circuits, Fig. 1 (not shown), an optical, radar, ultrasonic, or capacitive detector operates a solenoid switch which actuates two further solenoids arranged in parallel each in parallel with a capacitor. The capacitors are of such value as to maintain current flowing through their associated solenoids, and so maintain switches closed, for two different periods of time, so that if a following vehicle operates the detector during these time periods, appropriate signals are given. A timer may be included in the circuit to measure and record the time interval between the vehicles. In an alternative electronic system, Figs. 2-3 (not shown), passage of a vehicle over an inductive coil produces an increase in the frequency of a resonant circuit and an output from a frequency diseriminator which is led through an amplifier and voltage limiter to a differentiation circuit which generates a positive voltage spike in response to the leading edge of a vehicle and a negative spike in response to the trailing edge. Each negative spike triggers two one-shot multivibrators which generate timed pulses which are fed to AND circuits, the other inputs to which are produced by the positive spike when a vehicle arrives at the detection point. This system may be made inoperative when vehicles are travelling below a certain speed.