Railway infrastructure and vehicle maintenance expenditures are estimated to cost over 20,000M€ per year at European level. This indicates the demand for developing a low-cost system capable of providing prognostic information about the health status of the railway at the points of the interaction between the vehicle and the infrastructure (wheelset, pantograph, rail and catenary). To achieve these capabilities, SIA (System for vehicle-infrastructure Interaction Assets health status monitoring) is being developed by a consortium from five different European countries. Within the SIA system, events are captured by a network of sensors, which are time stamped and then accurately geo-referenced by the positioning sub-system of SIA. The positioning sub-system is based on EGNSS positioning algorithms tailored for the railway environment and comprises onboard as well as back-office processing. GNSS-based positioning in the railway environment is very challenging. Hence, Galileo with its advanced signal structure is utilized in SIA (in addition to GPS) to improve availability as well as accuracy. The onboard positioning algorithm has been developed based on a novel GNSS-IMU hybridized approach. The new approach can overcome frequent measurement gaps within the GNSS observations and maintain the accuracy level required by SIA system. An overview of the back-office positioning in SIA complements the presentation of the onboard processing.