What we mean by recycling data is taking data that has once been recorded and reusing it in the same or a different context. Consequently, data doesn’t have to be saved multiple times and data chains are generated that facilitate the efficient handling of data. For example, aircraft record weather data so that they can get safely from one place to another. It is a known fact that weather forecasts are less accurate when there is less flight traffic, which shows that this data is also used for weather forecasting. This in turn had an effect on our project with the Verkehrs-Aktiengesellschaft Nürnberg (VAG), which runs the public transport network in Nuremberg. During the project, it was discovered that changes in air pressure caused changes in the air resistance in the subway tunnel, which in turn affected the energy consumption of a subway train. If the aim is to optimize the energy efficiency of the subway timetable and the way subway trains are operated, it is necessary to take weather data into account; looking at the data chain in its entirety, we see that flight data from aircraft helps optimize the energy efficiency of subway trains.