A Binocular License Plate Reader for High Precision Speed Measurement

Abstract

The paper describes a vision processing system for traffic speed computation. Vehicle tracking is performed by using high-level features, that are clusters of license plate characters to achieve increased robustness of the system. By using a binocular arrangement of the Computer Vision system, the spatial and temporal range of image capture between consecutive views is extended, which leads to an improved accuracy in speed computation. Multiple views can be collected, from the same vehicle in transit, depending on the amount of speed. The effectiveness of the proposed solution is demonstrated through a geometric simulation model, where almost all operating conditions and constraints are fully exploited and tested. An error sensitivity analysis is carried out, to identify the most critical components of the system and the possible sources of errors in speed computation. This simulation approach is proved quite useful in this complex scenario, where it is commonly very difficult to collect true speed measures from the vehicles in transit. Beside the simulation analysis, a series of experimental results have been collected by a first prototype that is available since the end of year 2000.