Although traffic detection systems have advanced a long way during the last few years, the need for increased capacity within the existing road infrastructure is driving the demand for more intelligent sensors. This article considers the present range of detectors and some possible future developments. To illustrate some possibilities, it considers only the urban traffic situation, where the widest range of applications can be found. Urban traffic control focuses on junction management, and aims to keep the smallest number of vehicles stationary for the shortest time period. To minimise stop-start delays and resulting vehicle emissions, the ideal is to maintain a steady flow at an even speed for the highest directional demand. A wide range of technologies can now be used for the accurate and reliable detection of vehicles required to implement such traffic control. Detection technologies can be divided broadly into subsurface and above-ground methods, with each type having its own advantages and disadvantages. Subsurface technologies usually rely on a simple sensing function at the desired point of detection, with a separate remote signal processing unit, perhaps in a signal controller. Above-ground methods are very cost-effective for multiple function and zone ability. Cost-effective, multiple-function, selectable-function, addressable, intelligent detectors are already available.
Abstract