Within the project Greenlight the Austrian Federal Railways have equipped a large number of trains with high-quality dual-system single frequency receivers with RTK-capability. The goals of this project are manifold comprising the real-time train positing to support passenger information systems or the online monitoring of cargo and many more. In near future several hundreds of additional vehicles will be equipped with such receivers. Although the current configuration is based on GPS/GLONASS receivers the upcoming generation will consist of combined GPS/Galileo single frequency receivers. On basis of real observation data gathered along various railway tracks in Austria this presentation studies the potential of deriving tropospheric delay information useful for numeric weather models (NWM). The challenges are to retrieve tropospheric parameters (in first place vertical delays) with sufficient accuracy from data tracked by a fast moving object as well as the real-time or close-to-real-time data transmission between train and processing center. Further problems arise due to signal masking, multi-path and the required modelling of the ionospheric delay. On the other hand, compared to the current static networks of a few high-quality meteorological sites and several GNSS reference stations, the beauty of the solution is to make use of a fleet of almost 1000 GNSS sensors permanently moving over the Austrian territory. The presented study is based on post-processed raw observation data. Nevertheless, taking into consideration the upcoming 5G-network roll-up also a fast data transmission, at least when the trains pass railroad stations, can be assured in future. Aside of the discussion of quality aspects of the delay parameters derived from GPS/Galileo L1/E1 data also a NWM data assimilation step based on a few hundreds of simulated delays will be presented.