Satellite navigation plays a critical role in new railway signaling and train control systems. It will allow higher levels of automation at a reduce cost in installation and maintenance as compared to current infrastructure-based technologies. However, in order to be integrated in railway systems, GNSS must guarantee the stringent railway safety requirements. GNSS safety has been extensively quantified for the aviation community, however, in the railway environment the probability of local GNSS hazards like interferences is larger due to its operation in a non-restricted space. Railway GNSS receivers must be therefore equipped with mechanisms to protect the position determination from being corrupted by undesired interferences (jamming or spoofing) without being aware of it. In this paper and based on Commercial-Off-The-Shelf (COTS) hardware we implemented interference detection functions suitable for railway localization. We detail the algorithm design as well as the necessary calibration procedure to determine the nominal signal model. The performance of the interference detection is analyzed with an experimental setup on a commercial train during the measurement campaign organized for the EU project ERSAT-GGC. Figures about the detection capability and detected events along the selected line are finally provided.