New technologies such as GNSS-based positioning solutions will contribute to the modernization and efficiency enhancement of the railway system. Its capacity to provide a global absolute position without any infrastructure to be supported by the user at reasonable cost makes GNSS a game changer for rail. However, in order to reach the high-level performance requirements needed to apply these technologies to safety-critical applications, and in particular, for the use of virtual balises, some solutions need to ensure their accuracy, robustness and safety. Coming from aeronautics experience, the RAIM (Receiver Autonomous Integrity Monitoring) can help reducing inaccuracy by detecting and excluding faulty measurements and bounding residual errors. In this paper, we intend to demonstrate how the combination of weighting schemes and FDE (Fault Detection and Exclusion) can help the system to enhance GNSS performance in a railway environment where multipath, non-line of sight signals and interferences can occur. Some results based on real data are presented in order to quantify the benefit. Application of such techniques will help designing future on-board location units by evaluating their potential performance before deciding the level of hybridization that will be mandatory to ensure continuity of service and compensate the drawbacks of GNSS in harsh environments.