A new loop-detector circuit for improving low-speed performance.

This paper designs a new loop-detector instrumentation circuit using the so-called M-method, to improve the detection rate at low vehicle speeds, including bumper-to-bumper traffic situations. The developed circuit combines a phase-shift detection method using the conventional phase locked loop (PLL) circuit with a frequency-shift detection method using the so-called M-method for the first time. This allows accurate collection of traffic data for all vehicle speeds. The developed system has been tested on a national highway in Korea. Based on extensive experiments, it is shown that the new loop-detector circuit enhances the performance in obtaining the individual vehicle information at both low and high speeds. (A*)