Detector technology

General

In traffic detector information is derived from technologies divided into two main groups, information collected via in-situ detectors, deployed at location of interests, or information from mobile technologies that are located within vehicles themselves. Over the last two decades, there has been an increase in the provision of services that are specific to vehicle types, as well as fleet or asset management and tracking, based on in-vehicle technologies. In-vehicle technologies have really come into realization through the advantage of satellite-based technologies, and are perceived as playing an increasing role in the future.Such technologies not only improve our ability to manage networks efficiently, but will also have a direct impact of the types of policy instruments available to authorities, the operation of so-called ITS.

In-Situ Technologies

In-situ traffic detector technologies are further divided into two categories: Intrusive technologies that are physically mounted at, or below, the road surface, installation of which causes potential disruption to traffic. Conversely, non-intrusive technologies are mounted at, or above the road surface, and their installation causes little or no disruption to traffic. Detectors of both types temporary or permanent nature, though sub-surface intrusive installations are, by necessity, usually permanent. All in-situ detectors will provide some measure of the volume of vehicle flow. Particular detector technologies will vary as to their reliability of the flow estimate, and their ability to provide accurate additional information on vehicle category or speed. A single sensor gives only flow or occupancy information. Two adjacent sensors are required for speed or classification assessment. The time-lag and separation distance between the onset of consecutive events at the sensors have been used to estimate vehicle speed. Classification information is derived either from vehicle length or through examination of the form of the profile generated as output from the sensor.

Intrusive Technologies

Typical examples of intrusive technologies, their sensor types and installation locations are shown in Fig.

. The first types of units (Fig.

, Type 1) are passive magnetic or magneto-meter sensors that are either permanently mounted within holes in the road, or affixed to the road surface in some fashion. The unit communicates to a nearby base station processing unit using either wires buried in the road, or wireless communications.