As part of the eHighway Schleswig-Holstein (FeSH) field test, it was observed that the use of gritting agents on the highway leads to a salty severity on the insulators, which in turn results in leakage currents. To investigate the leakage current events, the Technical University of Dresden and Siemens Mobility GmbH developed a measuring system for long-term measurements and installed it at two locations on the system. This measuring system has since also been used in local transport systems. This article describes the structure of the measurement system, the evaluation methodology used and the main results of the investigations.