Train speed and position evaluation using wheel velocity measurements

A security system called SCMT, to be installed on trains circulating on Italian railways is being developed. One of the components of SCMT is a module for estimating train speed and positions between two subsequent viapoints equipped with balises which communicate to the train the distance to next target(s) and velocity requirement(s) at target(s). The module uses two wheels equipped with incremental encoder-type sensors. We describe an algorithm for position and velocity estimation capable of compensating for poor wheel-rail adhesion conditions due to rain, fog, ice, leaves, and so on, where conventional odometry algorithms fail. The system was designed and trained using a wide set of experimental data, conducted using different types of vehicles and conditions (in particular, degraded adhesion conditions were investigated). In each experimental test the velocities of four wheels and the real train were measured. The main goal of the system proposed in the paper is to evaluate the train speed and position on the basis of two wheel velocities information also in the case of wheel slipping or skidding. The system can estimate train speed and position also in case of failure of one of the two velocity sensors. The velocities of the two wheels must be periodically re-aligned to the real train speed, during a phase in which wheels are not slipping, in order to compensate for variations of wheel diameters