Introduction of GNSS in Railway Safety of Life Applications: Virtual Balise Detection in ERTMS

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The European Rail Traffic Management System (ERTMS) is an interoperable European train control and command system, with the objective of providing cross-border interoperability of trains while increasing safety, efficiency and reducing costs. ERTMS consists of two basic components: the European Train Control System (ETCS), an automatic train protection system providing in-cab train control; and GSM-R, a radio system for providing voice and data communications between the track and the train. Interoperability has been a key driver for ERTMS; through the creation of harmonized and transparent rules for railway operators and supply industry, ERTMS has seen significant worldwide adoption. GNSS is amongst the “game-changing” functions detailed in a report from the European Union Agency for Railways in 2015 on the longer-term perspective for the evolution of ERTMS. To ensure that an enhanced ERTMS with GNSS is interoperable and protects existing investments, the supply industry has been working on the realization of a virtual balise concept. Balises are physical transponders placed on the track providing absolute location reference to the train’s on-board system, allow a train to locate itself within a movement authority, and transmits static data to the train’s on-board system. The virtual balise concept is where a physical balise is replaced by a virtual analogue, resulting in a reduction of physical elements on the track, thus in principle saving costs. GNSS is perceived as a strong technological candidate to be introduced in Railway Safety of Life (SoL) applications, in particular for virtual balises. This paper presents results from the recently concluded RAILSAFE project, an activity initiated by ESA with the objective of assessing different GNSS-based technologies and augmentations in terms of their ability to mitigate system-level threats, and their potential performances. The paper is divided in three main sections: • First, a short description of the virtual balise concept is provided, the relevant use cases for GNSS are identified and the respective PNT requirements are summarized. • Second, the potential GNSS technologies that could be introduced for balise virtualization are identified, a safety performance assessment is provided and a theoretical performance analysis is conducted by running service volume simulations. • Third, the main conclusions and recommendations are summarised.