A new passive traffic detector

There has been an increasing need to improve traffic flow within urban centres without increasing the required roadway infrastructure. As a result of this requirement, automated traffic control systems have been evolving at a steady pace. Central to the operation of any automated traffic control system is the need to reliably detect vehicular traffic flow. Currently, this detection function was primarily carried out through the use of buried inductive loop sensors. Buried inductive loops have been in service for many years. Inductive loops typically require stopping or re-routing traffic during installation and are prone to breakage as a result of weather-related effects or construction. A variety of sensors have been developed for the replacement of buried loops. Of the technologies being employed in these sensors, those normally associated with all-weather day/night capability are radiating (active). Active sensors pose a certain degree of public health concern and are hence not a favoured solution. This paper describes the design and performance of a new, overhead vehicle sensor which relies on naturally occurring radio emissions. The sensor, mounted in an overhead or sidefire position, is intended to provide all-weather, day/night vehicle detection without any potential for public health safety impacts. Prototype test results are presented from a number of trial sites in varying weather conditions.