The single train shortest route problem in a railyard

Abstract

We consider the problem of moving a connected set of railcars, which we refer to as a train, from an origin layout to a destination layout in a railyard, accounting for the special structure of the railyard network and the length and orientation of the train. We propose a novel shortest path algorithm for determining a sequence of moves that minimizes the total distance (and associated time) required to move a train from its origin to destination. A railyard network consists of a set of track sections connected via switch points, which correspond to points at which three sections of track come together, such that one pair of the track segments forms an acute angle (and the other two pairs form obtuse angles). A train’s ability to traverse a switch node depends on the train’s length and whether or not its desired route involves traversing the acute angle or an obtuse angle at the switch. The shortest route problem for a train is further complicated by the fact that a train’s position on the network at any point in time may span multiple nodes in the network. We propose an easily explained solution approach that addresses the complications associated with switch points and the train’s length to determine a shortest route from origin to destination in ${\mathcal {O}}(e + n \log n)$ operations, where n and e correspond to the number of switch nodes and edges in the network respectively.