Analyzes the arrival process of wagons in the sorting sidings of a marshalling yard. Based on this analysis a wagon collecting model is worked out, with fixed collecting periods for outgoing trains. The model makes it possible to relate the load factor of the outgoing trains to the time spent by the wagons in the sorting sidings, i. e. to determine the necessary technical parameters, as is demonstrated by examples. An alternative process of wagon collecting is also described, in which the standard maximum train load is strictly respected. The results of this method are investigated.