Patent ID: 7835853

Claim:
A vehicle detection system for detecting a vehicle running through a monitoring range on a road, comprising: a sensor detecting infrared radiation irradiated from an object to be detected; a background level calculation means that (a) defines the intensity of current infrared radiation detected by the sensor as an input level value, (b) defines a value based on the intensity of infrared radiation emitted by objects other than vehicles as a background level value, and (c) calculates and renews the background level value in accordance with the last result of a vehicle presence judgment by using the input level value; and a vehicle presence judgment means that (a) defines a value based on the difference between the input level value and the background level value as a comparative value and (b) determines the presence of the vehicle when the comparative value exceeds a threshold value, wherein a value defined by adding a modification value to a set value is used as the threshold value and the modification value is changed depending on the last result of the vehicle presence judgment.