Abstract
Three different physical phenomena are discussed as applied to the detection of roadway vehicular traffic. These detectors are the input data sources for vehicle-actuated traffic signal light control mechanisms, control systems, freeway surveillance, and statistical analysis. Radar detectors using microwave radio frequencies in the 2.5-10 MHz range are discussed with regard to operating principles, design considerations, and practical application. Similarly, the acoustical detectors operating in the 20 kHz range, and also the low-flux density change magnetic detectors are described. Finally, a comparative analysis is made of radar, acoustical, and magnetic detectors as well as mechanical, magnetic, induction, and optical detectors.