Importance

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Abstract

Apparatus (10) for monitoring vehicle (V) usage on a roadway (H). An AC light source (12) comprises either an incandescent or gas discharge light source. The light source has a detectable AC ripple in its output. The light source is mounted or installed above the roadway surface on a conventional light standard (16) or highway information standard (18) such that the light source directs its rumination downwardly onto the roadway. A light detector (34) detects light reflected from off the roadway. Light from the light source together with the collection optics of the light detector define a 'footprint' (30) on the roadway surface and vehicles moving over the roadway pass over this footprint. The directed, reflected light has characteristics which are varied in response to passage of a vehicle over the roadway and through a path (X1, X2) of light between the source and detector. A processor (52) processes the reflected light and is responsive to variations in the characteristics of detected, reflected light caused by vehicle passage. The processor is capable of determining the number of vehicles passing over the roadway surface during a predetermined period of time, the speed of the vehicles, and the type of a vehicle. Further, the detector and processor are sensitive to changes in atmospheric conditions to adjust detection thresholds so the apparatus maintains its responsiveness to the passage of vehicles.

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First Claim