Roadside Sensors for Traffic Management

Knowledge of modern traffic flow sensors is key to providing traffic managers, researchers, and students the ability to understand the operation, installation requirements, strengths, and limitations of current sensor technologies to enable an informed decision as to which is appropriate for a particular application. Accordingly, this paper describes the in-roadway and above-roadway traffic flow sensor technologies, their applications and selection criteria, typical output data, and models representative of each technology. Accounting for life-cycle costs ensures that not only direct hardware and software purchase costs be considered, but also that installation, training, maintenance, and repair are factored into the sensor selection decision. The technologies discussed are mature with respect to current traffic management applications, although some may not provide the data or the accuracy required for a specific application or may not perform as needed under the environmental conditions anticipated at the installation site. Sensors selected for a first-time application should be field tested under actual operating conditions including variations in traffic flow rates, night lighting, inclement weather, and unique road configurations that may be encountered in day-to-day operation before large-scale purchases of the device are made. As alternative traffic data and information sources become increasingly available, they are progressingly finding their way into modern traffic management systems as a complement to conventional roadside sensors.