US Patent 11836569 Vehicle tracking system using smart-phone as active transponder

A system combining readers for RFID transponders and Bluetooth® devices for for automated roadway tolling and monitoring is described. Because of the ubiquity of Bluetooth® devices, filtering methods are described to narrow received Bluetooth® signals to a particular monitored traffic lane and to further associate the Bluetooth® signal with a registered RFID toll tag in a vehicle. Signal strength of the Bluetooth® signal at each of a plurality of receiver antennas may be used to identify the location of the Bluetooth® device that emitted the signal.