Automatic vehicle identification (AVI) technology, which permits fully automatic and unique identification of vehicles at specific interrogation points, offers potential benefits in many fields including fleet control, revenue collection, traffic operations, transportation planning, and safety and law enforcement. Three technologies are currently being used for AVI: optical, microwave, and low power radio frequency. All of the three technologies are currently being used in either operating systems or extensive field testing under operating conditions. The first large scale application of AVI was in the railroad industry to identify automatically rolling stock. The optical AVI techniques used have also been applied in automatic container identification and, in a limited scope application, in the operation of an automatic toll collection system. Microwave AVI techniques have been tested successfully in containerization applications and are currently under test by a major toll road in revenue collection application. Low power radio frequency AVI was tested extensively in the federally-sponsored Automatic Bus Identification Project and is being evaluated for nonstop toll collection application by toll agencies. While the cost effectiveness of AVI will vary to a considerable extent with the technology used and the desired functional requirements, existing AVI technology can provide automatic unique identification of vehicles at a cost which can be justified in many applications. As these applications are being developed, the rapid advances in computer and electronic technology which are inherent in AVI systems, will further reduce initial and operating costs of contemplated AVI systems.