ERTMS/ETCS Level 3: Development, assumptions, and what it means for the future

The purpose of this paper is to categorize the research on Level 3 and Hybrid Level 3; map how the research focus on ERTMS Level 3 has developed over time; summarize key assumptions in research on Level 3 and Hybrid Level 3. This study uses a scoping review approach. This review method provides a comprehensive overview of the literature in a selected field. The literature searches in this study were primarily conducted in Scopus and Web of Science and were complemented with a follow-up search in Google Scholar. The topics are divided into two thematic areas: Effects on the Railway System and Technical Requirements. The thematic area Technical Requirements is further divided into the following subcategories: train, trackside, and communication. The effects on the railway system are measured using performance indicators: capacity, stability/robustness, and safety. ERTMS Level 3 has developed from a pure Level 3 to Hybrid Level 3. Hybrid Level 3 represents a pragmatic solution, but it may emerge as a threat to the long-term objective of the Level 3 moving block. Studies of Level 3 are based on a moving block solution, while studies of Hybrid Level 3 are mainly based on virtual sub-sections. Both Level 3 and Hybrid Level 3 studies tend to make assumptions that risk missing wider aspects of the railway system. There is also a need to correctly represent different ERTMS Level 3 configurations to ensure expected capacity gains. For a better understanding of the development and future path of ERTMS Level 3, it is interesting to study the following aspects: the historical development of ERTMS Level 3 research, the assumptions made about ERTMS Level 3, and the conditions and restrictions under which ERTMS Level 3 will be implemented. Assumptions and simplifications are necessary for modeling work, but there is also a need to highlight underlying assumptions in analyses of different ERTMS Level 3 configurations.