Safety concept of railway signalling based on Galileo Safety-of-Life Service

The Safety-of-Life (SoL) Service - Level A of the satellite navigation system Galileo has great application potential for both aviation and railway safety-related systems with view to reduce operational, investment and maintenance cost. In aviation sector, radio navigation has been widely used for safety applications for several decades. That's why main quality requirements regarding the Galileo Signal-In-Space (SIS) SoL service - Level A, such as accuracy, integrity, continuity and availability, were taken from aviation ground radio navigation systems. However, different safety philosophies used in aviation domain and in railway signalling complicate direct employment of the Galileo quality measures to railway safety applications. The objective of this paper is to show, what are fundamental differences between aeronautical and railway safety philosophies from view point of Global Navigational Satellite System (GNSS) applications, how the Galileo SIS quality measures were derived, what is their practical meaning and how it is possible to employ them for practical design of a safe Train Position Locator (TPL). The safety assessment starts from classification of Galileo SIS integrity and continuity risks by failure modes. It is shown how integrity and continuity risks influence railway safety and what impact these risks have on dependability of a safety-related system. The interpretation of the Galileo quality measures in terms of RAMS (Reliability, Availability, Maintainability and Safety) according to the standard EN 50126 is proposed. Finally, the practical application of the Galileo quality measures for safety assessment of a TPL is demonstrated.