Weeds can have detrimental effects on the railway infrastructure. This mainly through the accumulation of humus, which can increase water retention and may damage both sleepers and rails, as well as the overall stability of the ground. Ultimately, these factors can result in track deformation, which directly influences the speed at which trains are able to travel. In Switzerland, herbicides are predominantly utilized for weed control, although alternative methods such as mechanical and thermal techniques are also employed. Currently, glyphosate is the only herbicide used to remove weeds from railway tracks, which has proven to be relatively effective. However, uncertainties concerning the renewal of authorisations of the substance in Europe have prompted railway companies to explore alternative herbicides that may replace glyphosate. Due to the inherent permeability of railway tracks and therefore increased net infiltration, it is important to choose herbicides with a low risk of leaching to groundwater. The characteristics of a suitable herbicide include thus a high sorption in the soil and/or rapid degradation (also for metabolites), as well as low application rates. In order to help decision-makers to make informed decisions, we constructed ten lysimeters with railway materials from three locations, allowing us to study the leaching behaviour of herbicides in close-to-real conditions. Using liquid chromatography–mass spectrometry, we investigate the leaching potential of 12 alternative herbicides and their main metabolites. The selected group of alternative herbicides includes six auxin-mimics, three acetolactate synthase inhibitors, as well as three pigment-synthesis inhibitors. One a year after the first application of the substances in May 2023, we observe that leaching is influenced by both the lysimeter soil properties and the herbicides used. While some of the herbicides have already reached their maximum concentrations under all soil conditions, some have not been detected yet. These undetected herbicides may have degraded completely or may still elute later. The project will continue for at least 2 years (from the time of the first application) and will allow us to conclude on the leaching potential of the applied substances and their metabolites under realistic conditions. Moreover, the project will allow a direct comparison of all applied substances under identical weather conditions in 3 different soil types.