Monitoring a metropolitan freeway system using probe vehicles and random access radio channel

The lack of proficient real time traffic monitoring systems is one of the major bottlenecks of Advanced Traveller Information Systems (ATIS) and Advanced Traffic Management Systems (ATMS). The authors describe and analyze the performance of a method for collecting real-time traffic data from probe vehicles automatically sending traffic reports to one or more base stations, connected to a traffic center by a wired communications network. The results reveal that random access (ALOHA) transmission of traffic reports is a (spectrum) efficient, inexpensive and flexible method for collecting road traffic data and that this approach can provide reliable traffic monitoring. Not only highly accurate real time link travel times can be estimated, but also Automatic Incident Detection (AID) can be performed