Distributed surveillance on freeways with an emphasis on incident detection

Efficient management of a road network requires continuous decision-making based on conditions on the network and an understanding of the impacts of the decisions made. These conditions are usually measured with fixed-point surveillance systems, most of which are deployed in such a manner as to require communication links that are always connected and are polled at regular intervals. All of the sensor data are typically sent to a traffic management center (TMC) for assessment, yet most of the time no action is taken in response to the data, leading to unnecessarily high communication costs. To reduce communication costs without a significant loss in the quality of information received at the TMC, this paper lays the foundation for an event driven communication system by examining the information value of specific events at the detectors. This procedure can then be used to offload a portion of the decision making from the TMC to the field controllers, which would make the initial valuation of information and only send data that might elicit a control response or benefit comparative decisions between detector stations. In other words, rather than relying on the conventional, centrally polled communication system, these events could be used to initiate communication from the field when the potential value outweighs the cost per communication. The information value could also lead to better data handling for decision-making or archiving in a conventional, polled communication system. We develop the methodology by deconstructing an incident on a freeway and identify the observable events at a pair of detector stations that may be upstream, downstream or straddle the incident. This analytical process could be repeated for any other condition of interest.