Dutch railway company NS on Wednesday said it plans to reduce its carbon dioxide (CO2) emission level further, having already achieved its own target of a 16 per cent reduction since 1997, reported dpa. NS chief executive Aad Veenman said the rail network's carbon emission levels in 2020 must be 20 per cent lower than in 1997. NS Railways operates 90 per cent of trains on the Dutch rail network that has seen a substantial rise in the number of passengers. Additional reduction had to be achieved through, among others, "storing" the energy produced when trains slow down. NS is in the process of acquiring train cars that have the ability to store and return energy to the railway network for use by other trains in the area. Veenman also said that in 2010, all paper used by NS would have to originate from so-called sustainable forests, ensuring new trees will be planted for each tree used for paper production.