Applications and Evaluation of Automated License Plate Reading Systems

Many technological advances have enabled new methods of collecting transportation data that can be used to plan and maintain effective roadway policies. Automated license plate reading technologies are beginning to gain acceptance because of the wide range of applications to which they can be applied. Typically, automatic license plate reading (ALPR) systems are used for enforcement type applications and data collection applications including parking lot management, origin-destination studies, traffic flow studies, high occupancy vehicle analysis, and weigh in motion systems. An ALPR system consists of three main components; a device for detecting vehicle presence, a digital video camera and an image processor. The image processor identifies the license plate according to embedded pattern recognition algorithms. The accuracy of the pattern recognition algorithms used in the image processor is an important concern when evaluating ALPR systems. The required accuracy depends on the application. For example, an enforcement application may require a high degree of accuracy while a traffic flow study may only require that an image obtained at an entry point be matched to an image obtained at an exit point. Other issues for consideration when evaluating ALPR systems are mobility and simplicity of use, range of vehicle types that can be read, necessary lighting conditions, range of states of origin that can be read, range of vehicular volumes and speeds that do not overload the image processor, and human impact/public relations.