Vehicle tracking system using smart-phone as active transponder

A system for tracking vehicle position using a smart phone in the vehicle as an active transponder, which is detected by roadside equipment is disclosed. In an embodiment, the system uses existing RF transceivers on the smart-phone, such as Bluetooth LE or WiFi to periodically transmit an identifying message. Road-based equipment detects and locates the smart phone. In a further embodiment, the smart phone is alerted by roadside beacons and only then responds with its identification information. Processing can be performed either on the smart phone or by roadside or central office equipment as is the case in prior art active or passive transponder-based tolling systems. Vehicle location detection can be enhanced through the use of directional antenna matrices such as a Butler matrix. The system can be used for automated roadway tolling and monitoring.