Advances in practical implementation of AVI systems

Electronic toll collection with reflective Automatic Vehicle Identification (AVI) tags in the vehicle windshield is a commercial reality, with proven reliability and cost effectiveness. Reflective tag technology enhances the selectivity for reading only the closest of several tags in the reader's field, as well as reducing tag complexity and cost. The advantages of reflective tag technology can be retained for the vehicle-to-roadside radio link of IVHS with a simple ASK radio link used for roadside-to-vehicle transmissions. System capability and reliability could be improved with the IVHS antenna designed into the vehicle structure. Usable vehicle speed and required RF power trade off against message length, making it necessary to use message data bits as efficiently as possible.