Vehicles traveling on toll roads as
well as free roads can be identified by their
identification (RFID) transponders commonly called a toll tags.
These devices provide a unique radio identification code when
read by AVI system equipment. Small yagi radio antennas pointed
at each lane can identify specific vehicles as they pass. These
antennas are most often attached to overhead sign structures,
overpasses, and toll gate structures. Portable trailer AVI
readers are also commonly used in construction areas and to
conduct temporary traffic surveys. Even handheld readers can be
used to query the transponder tags.