Road Traffic Monitoring by Satellite (RTMS) is an innovative trial system that uses a fleet of ‘tracer’ vehicles to detect congestion.
Using GPS positioning, an in-car computer and the ESA developed PRODAT mobile communication system, traffic data is reported via satellite to a central facility. Compared to conventional detection methods, a satellite-based in-car system offers better coverage and better data at potentially competitive costs.
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http://www.esa.int/export/esaCP/ESAU6T7708D_Benefits_0.html