A vehicle detector and classifier comprises a plurality of electrically conductive loops 1 arranged substantially in a plane perpendicular to a road surface, for detecting vehicle wheels. The loops can be arranged in a transverse, vertical slot 2 and housed in a flexible enclosure. An electronic circuit 3, including an oscillator, can be positioned adjacent each loop 1 in the slot 2 to energize and monitor the loop. The detector preferably also includes a conventional loop arranged substantially in the plane of the road surface, for detecting vehicle bodies, and means for superposing the results obtained from the conventional and vertical loops to aid in classifying detected vehicles.

A vehicle detector system having a number of individual vehicle detectors each capable of sampling a plurality of vehicle loops in mutual synchronization. One detector operates as a master detector for synchronization purposes; the other detectors are operated as slave detectors. The system can be configured for series or parallel synchronous operation. The system is particularly advantageous in installations requiring a large number of closely spaced vehicle loops each operated by a detector set to high sensitivity.

A wire-loop vehicle detector is configured with a vertically oriented blade aligned at an angle to the direction of traffic-flow with each end of the blade extending laterally beyond the normal limits of vehicle presence over the blade. The extended blade configuration of the wire-loop constrains over-passing vehicles to present repeatable inductive signatures while electromagnetic noise and thermal-drift are selectively canceled using a secondary coil to increase the signal-to-noise ratio of inductance measurements. Inductive signatures of vehicles are recorded using a high-speed and high-precision method of making multiple successive measurements of the inductance of a wire-loop as vehicles pass over. Inductive signatures of automotive vehicles are useful for parking-lot revenue control, car-bomb detection, passive security of isolated communities, and other traffic-flow monitoring and control applications.

Methods for a determining a normalized lane occupancy and for monitoring signal quality for a vehicle detection system. Such methods include, in one embodiment, measuring a speed of a vehicle with an inductive vehicle detector, measuring an on-time for the vehicle crossing a wire loop sensor of the inductive vehicle detector, determining an inductive length of the vehicle from the measured speed, and computing a normalized on-time by subtracting a longitudinal length of the wire loop sensor from the inductive length and dividing the difference by the measured speed.

Methods and apparatus for such that a measurement made for a given vehicle by a given detector is substantially repeatable using either the same detector from one time to another, or using a different detector. In one embodiment, normalization coefficients are determined by measuring one or more common probe vehicles and standardizing the outputs of the detector(s) to give a consistent output. In another embodiment, normalization coefficients are determined by measuring one or more operating or circuit parameters of the detector circuit(s), and compensating the outputs of the detector(s) for variations in these measured parameters.