Transport represents both need and threat to the modern human society. European transport policy aims at sustainable transport development based on the efficient use of natural resources, protection and improvement of environment, as well as the real and diverse needs of potential users. The paper points out that the development of railway infrastructure is a necessary but not sufficient condition for shaping the sustainable mobility. Railway infrastructure has to meet the requirements of the society, economy, protection and improvement of the environment. In general, electrification of railways leads to reduction of the carbon footprint. On the other hand, thermal power plants in Serbia are the main suppliers of electric power. The results of previous geotechnical laboratory testing showed that investigated fly ash could be suitable for utilisation in the railway infrastructure. This paper presents the results of laboratory tests to determine the presence of radionuclides and trace elements in fly ash samples.