Braking questions - ETCS Braking Curve Guideline

Currently, for virtually all cross-border trains in Europe operating at up to 200 km/h, the only information available in respect of the quantitative description of rapid braking performance is the braked weight percentage. The braked weight is usually determined empirically on the basis of stopping distances obtained in tests according to UIC Leaflet 544-1. It is an effective way of expressing the ability of any train to stop over a certain distance, when travelling at an initial given speed. However, this parameter does not provide information on the actual deceleration characteristics, which can vary widely depending on the braking equipment. An automatic speed-supervision system like ERTMS/ETCS requires knowledge of the braking performance of a train in terms of its instantaneous deceleration as a function of speed. It is therefore obvious that a solution has to be found using the braked-weight percentage (and, if necessary, other additional information) to deduce a reliable deceleration profile.

As a consequence, a mathematical model to describe the braking performance of all train categories running with ERTMS/ETCS has been developed on a theoretical basis and proofed and refined by means of test results.

To facilitate consistent use of the braking model, a guidance document was to be provided explaining the key input parameters to deliver reliable results taking into account the requirements of UIC Leaflet 544-1. The document also contains a comparison between existing signalling systems of different ETCS-equipped networks.

In addition the different types of safety factors are explained, including how they are used in the model to enable interim national values to be applied.

Last but not least, the system of braking curves is described in a general way, and likewise the influence of several braking-curve parameters is demonstrated.