The RUNE project: the integrity performances of GNSS-based railway user navigation equipment

The RUNE project (railway user navigation equipment) is aimed at demonstrating the use of GNSS integrity and safety of life service characteristics for defining a satellite-based system to perform train location for safe railway applications. ALS-Laben is leading a consortium for the development and demonstration of the RUNE equipment, under ESA contract. The project involves both a HW-In-the-Loop laboratory set-up as well as a 3 months field-testing on-board an experimental train of the Italian train operator Trenitalia. The primary objective is to demonstrate the improvement of the train self-capability in determining its own position and velocity, with a limited or no support from the trackside, and to show that the equipment can comply with the European Railway Train Management System requirements. The RUNE technical solution is based on GNSS receivers: navigation data will come from GPS with differential EGNOS corrections (European Geostationary Navigation Overlay Service) to enable autonomous and reliable determination of train position, velocity under practically all environmental conditions. The system will offer another technological approach for the train location function: the use of GNSS signals integrated with inertial sensors and on-board odometers, in an "intelligent" system of mutual calibration, error filtering and error correction, represents a technical, industrial and operational challenge. Availability and integrity requirements are the most challenging obstacles towards an ERTMS/ETCS compliant GNSS aided railway navigation equipment. RUNE is designed to take advantage of the current EGNOS integrity and wide area differential correction service and extend its availability through an hybrid navigation system based on GPS/EGNOS, INS and Odometer data processed by a navigation EKF. The achievement of such objective would lead to the reduction of the frequency of physical balises by replacing them with virtual ones, with a significant reduction of the infrastructure costs (initial investment and recurring maintenance costs), whilst still maintaining the level of safety currently provided. This will be made possible by RUNE by producing to the on-board train control equipment a balise-crossing message when a virtual balise is detected. RUNE will also assist the locomotive engineer on approaching signal locations on the basis of a track map, and on controlling the train velocity on the basis of allowed velocity profiles, with resulting improvements in the safety and security of operations. In the long run, RUNE is expected to provide real time/continuous information also to the railway traffic control centre on trains position and speed. This will permit not only increased safety and security of the operations, but also possible increases in operating speeds, increases in track capacity, reductions in conventional infrastructure investments and maintenance, fuel consumption reductions, enhanced fleet management, as well as improved customer service. This paper will focus on safety analysis of the RUNE demonstration prototype and can be considered as the basis for the building of the safety case of future signalling systems using RUNE functions.