Doppler and Radar Microwave Sensors
Doppler microwave detection devices transmit a continuous signal of low-energy microwave radiation at a target area and then analyze the reflected signal. The detector registers a change in the frequency of waves occurring when the microwave source and the vehicle are in motion relative to one another. This allows the device to detect moving vehicles.
Radar is capable of detecting distant objects and determining their position and speed of movement. With vehicle detection, a device directs high frequency radio waves at the roadway to determine the time delay of the return signal, thereby calculating the distance to the detected vehicle.
Studies show that microwave sensors provide practically accurate traffic counts in normal weather conditions, however, their accuracy may decrease significantly in adverse weather conditions.1
1Chang, D.K., et al., Use of Hi-resolution data for evaluating accuracy of traffic volume counts collected by microwave sensors, Journal of Traffic and Transportation Engineering (English Edition) (2017), http://dx.doi.org/10.1016/j.jtte.2017.06.002