This paper investigates the correlation between the results of a diagnostic system for overhead line, previously developed, tested and installed on both high-speed and commuter commercial trains, and the standard measures of overhead line geometry carried out by an inspection train. The diagnostic system proposed is rolling stock based, and adopts pantograph collector accelerations to calculate diagnostic indicators of the status of the overhead line. These indexes are computed in real time during the train run by suitable algorithms, and compared with threshold limits. The set-up proposed is inexpensive and easy to install on commercial service trains, aimed at marking an improvement on current time-scheduled methods for quality assessment of infrastructure