The Norwegian Railway Administration (JBV) uses a measuring car to measure track performance. From a safety point of view, special attention needs to be paid to spots on the line where failure propagation is out of control, and critical failures could develop in between measurements typically carried out twice a year. A challenge in the modelling is that we are dealing with so-called line objects, where there are an almost infinite number of places a failure can occur. This is complicated by the fact that the measuring car reports the position of failures with some uncertainty, making it...