Certification of egnos safety-of-life service for ertms according to iec 61508 and en 50129

Abstract

A number of research projects are currently focused on the replacement of track balises (used for safe train position determination) with Virtual Balises (VBs) detected by GNSS to increase the efficiency of the European Rail Traffic Management System (ERTMS). The exploitation of the EGNOS Safety-of-Life (SoL) service, which is the European GNSS wide-area augmentation developed for aviation, for Virtual Balise Reader (VBR), should further strengthen the interoperability of ERTMS. In order to meet the high Safety Integrity Level required for VB detection (SIL 4), EGNOS-based train position determination in combination with other on-board sensors must be used. The adoption of EGNOS, which was not designed according to CENELEC railway safety standards, shall pass through a railway certification process to demonstrate that all demands on safety, dependability and interoperability have been met. This article proposes certification of the EGNOS SoL service for ERTMS via a so-called “pre-existing” item in the sense of the IEC 61508 and EN 50129 standards. The pre-existing item means an item that already exists and that was not specifically developed for the current project. The proposed solution starts with the use of Common Safety Method for Risk evaluation and Assessment (CSM-RA) that must be applied according to the EU Regulation No. 402/2013, because the safety change in ERTMS is significant. Since EGNOS alone is not able to meet the safety integrity requirement for VB detection, then EGNOS shall be correctly integrated within the VBR constituent. This article suggests that all essential information on EGNOS required for its integration into the VBR subsystem would be contained in the EGNOS Safety Manual. The Safety Manual, together with its assessment report, would be then referred in the section entitled “Related Safety Cases” of the overall Safety Case according to EN 50129.The presented results contribute to the introduction of EGNOS into ERTMS.