The Heidekrautbahn railway in Berlin is undergoing a significant transformation by replacing diesel railcars with fuel cell multiple units powered by 'green' hydrogen starting from December 2024. The initiative, part of the 'H2BAR' project, involves the use of regionally produced hydrogen from wind and solar energy sources. Led by the German Aerospace Centre (DLR) in collaboration with the Brandenburg University of Technology Cottbus-Senftenberg, the project aims to assess the practicality, costs, and environmental impact of this alternative rail transport solution until 2035. The project participants, including Niederbarnimer Eisenbahn (NEB), ENERTRAG, and Barnimer Energiebeteiligungsgesellschaft (BEBG), are optimistic that the emission-free trains will save approximately one million litres of diesel fuel annually. A recent media ride at the InnoTrans trade fair showcased the potential of the fuel cell trains, manufactured by Siemens Mobility, to enable CO2-free railway operations without significant infrastructure expansions. DLR's involvement in designing the hydrogen refuelling station and analyzing data from both the fuel cell trains and existing diesel-powered trains underscores the comprehensive approach to evaluating the transition. The installation of measurement technology in the trains and refuelling station will provide real-time data for detailed analysis, aiding in optimizing vehicle operation, infrastructure utilization, and cost efficiency. The project anticipates that the long-term costs of fuel cell trains will be comparable to diesel trains, paving the way for sustainable and economically viable rail transport solutions.