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A note on “Multistage Methods for Freight Train Classification”

The paper “Multistage Methods for Freight Train Classification” by Jacob et al. [Networks 57 (2011) 87–105] provides great insight into the theory and practice of sorting procedures at shunting yards. In Jacob et al. [Networks 57 (2011) 87–105] many relevant shunting situations (e.g., single or multiple inbound trains, single or multiple outbound trains, (un)restricted number of tracks, (un)restricted track capacity) are formally specified as optimization problems. Then, for almost all of them either an exact polynomial‐time algorithm or an NP‐hardness proof is provided. However, the case of multiple inbound trains, which is of high practical relevance, is left open. We close this gap by providing a proof of NP‐hardness. © 2013 Wiley Periodicals, Inc. NETWORKS, 2013