California Partners for Advanced Transportation Technology

In this report, the authors describe a method of collecting real-time traffic data from probe vehicles automatically sending traffic reports to one or m ore base stations, connected to a traffic center by a wired communications network. Analyzing and computing road traffic and message traffic flows in the San Francisco Bay Area, the authors study several multi-disciplinary aspects of this data collection technique. The results presented in this report reveal that random access (ALOHA) transmission of traffic messages is a (spectrum) efficient, inexpensive and flexible method for collecting road traffic data and that this approach can provide reliable traffic monitoring. This method allows for the estimation of highly accurate real time link travel times and Automatic Incident Detection (AID) can also be performed.