A system is described for tracking vehicle position using a smart phone or similar device as an active transponder that communicates with roadside equipment. The system may 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 aspect, the smart phone is alerted by roadside beacons and responds with identification information. Transaction processing may be performed either on the smart phone or by roadside or back office equipment. The system may be used for automated roadway tolling and monitoring and also for access control. A coded card may be scanned by the smart card to enter identification for access control.