Within the next few decades, railways will undergo a major modernisation in order to increase their efficiency and safety. The modernisation process will enable new concepts such as fully autonomous trains and dynamic coupling of consists. Today's centralised railway management systems will not be able to safely handle these train concepts and, thus, will be replaced or complemented by new systems. These systems require a tight train monitoring which is based on the reliable exchange of information covering among others the accurate position and velocity of trains. The authors are sure that modern train concepts demand both reliable train‐to‐train (T2T) communication and improved capabilities for train‐to‐ground communication. However, T2T communication is hardly investigated and so far no technology has been selected. With this publication, the authors like to provide more insight into T2T signal propagation. This is the basis for the future development of a modern T2T communication system. The authors focus on wide band propagation for T2T scenarios and describe an extensive channel sounding measurement campaign involving two high speed trains. Results on signal propagation measurements in high speed T2T scenarios are presented for different environments. Hence, path loss models for rural, sub‐urban and tunnel environments are introduced.