As climate targets become more and more ambitious, rail is rapidly emerging as the best way to attain them: No other mode of transport offers such energy-efficient mobility. But although trains already have considerable green credentials, there is further scope for improving their environmental footprint by reducing energy consumption, cutting noise emissions and making added-value chains more resource-efficient. LOWER MASS, LOWER ENERGY CONSUMPTION There is one obvious way to cut the energy consumption of a railway vehicle: by reducing the weight of its systems, products and components. Any mass that does not have to be accelerated does not require energy to be expended. Especially for metro trains, which operate with frequent phases of acceleration and braking, the reduced translational and rotational mass of light-weight aluminum brake discs can bring significant energy savings. On the new trains recently delivered to Hong Kong Metro (Fig. 1), for example, Knorr-Bremse has achieved weight savings of more than 400 kilograms per car. It is a win-win situation in both economic and environmental terms: Although the initial cost of purchasing aluminum brake discs may be higher, the bottom line is lower, because of the long-term energy savings.