Speed and positioning systems. The traditional way

This paper gives a summary of traditional speed and position measurement for railway systems. The intention is to give an introduction to nonrailway experts. The safe operation of the trains in railway traffic is essential and the accuracy in speed and position measurement is one of the main conditions for that. Traditionally the measurements and calculations are made on the train, and the results are compared with on board data to perform the correct actions. If the action is not correct and the situation becomes dangerous, the control system will stop the train. One of the problems with the existing systems is the inaccuracy in the measurements. This has been taken care of, by increasing the safety margin, and thus decreasing the capacity for the traffic. The inaccuracy mainly depends on slip and slide of train movements, which is a consequence of the low friction on the rails