Braking Problems - Calculations of the Kappa-factor for G braked trains longer than 700 m

UIC leaflet 544-1 4^th edition provides braking distances for G-braked and P-braked trains in relation to their braked weight percentage up till a length of 700 m.  For longer trains there exists no unified model to determine the stopping distances with respect to the braked weight percentage. 

To respond on the growing interest to operate trains longer than 700 m a model with Kappa values, similar as the existing one for P-brake trains up till 700 m of length, is created with the intention to be integrated in the 5^th edition of the UIC leaflet 544-1.

This new Kappa model is made exclusively for G-braked trains because trains longer than 700 m are expected to be operated with the G brake position to avoid excessive longitudinal forces.

The basis for the model are the stopping distances of G-braked trains from ERRI B 126/RP17 and the brake build-up times as determined by workgroup B 126.15D for trains with length up till 1 500 m as described in DT 423.

The necessary Kappa values seemed to be highly dependent on the initial Lambda and the speed of the train. The lower the Lambda and the lower the speed, the lower the Kappa-value should be. Taking the lowest Kappa values was certainly the safest option but low Kappa values would force the trains to run at very low speeds.

Therefore it was necessary to choose the Kappa values on the basis of an evaluation of the safety margins on different networks for all possible speeds.  The Kappa values were chosen in such a way that the safety margins remain within acceptable values. 

Safety margins being generally higher for low speeds, the Kappa values could be based on the normal operating speeds with the consequence that the safety margins are reduced for the lower speeds.

Due to the large number of variations in signalling systems, it was not possible, within the timeframe of the project, to foresee the exact impact of the Kappa value on the safety margins for all the existing signalling systems.

Depending on the signalling system, corrective measures may be necessary to maintain sufficient safety margins.

Therefore the workgroup recommended limiting the model with Kappa values for G-braked trains up till a length of 1 000 m of the hauled rake.