Railroad simulation is always challenging to modelers, since this kind of system has physical restrictions that cannot be ignored or deeply simplified without losing precision. The great difficulty on modeling the railroad behavior lies on the train movement, specially on single lines. This paper describes the experience of modeling a railway line used for coal transportation in Colombia, used by one of the largest openpit coal mining companies in the world, and the most important in the

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... : Carbones del Cerrejón. After experiencing and analyzing different options, the model was built with a signal-oriented decision process, where all train movements are allowed or restricted by the line signals. This approach made possible to represent every specific decision regarding the train movements in different sections of the line, using a simple local, instead of a global complex intelligence. It has proven to be very precise, fitting the real system with small error, and allowed several experiments to support decisions at Cerrejón.