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Path Selection
The Dispatcher follows a smart strategy, when it has to select one of several possible
paths. In Diagram 102, for example, the Dispatcher has to select one of three possible
paths, when a train is approaching the “Hidden Yard” from the west or from the east.
In the following the criteria which influence the selection of a path are listed. The following
aspects lower the chance of a certain path to be used or might prevent a certain
path from being selected at all:
• Other trains, that reserve one or more blocks and routes ahead of the train.
• Locks applied to the entry or exit of certain blocks (see page 110).
• Blocks or routes, that are reported as occupied by unknown objects; more severe, if
the rules specified for the schedule do not allow to enter occupied blocks or routes.
• Conditions, that prevent a block from being reserved or a route from being activated
(see the following section).
• The distance to an appropriate destination block.
• Superfluous loops.
There are also criteria, that raise the chance of a certain path to be selected:
• Blocks ahead of the train that have been already reserved for this train.
• Activated routes ahead of the train , that are not already reserved by other trains.
• The distance to the nearest obstacle listed in the previous list.
At first the Dispatcher evaluates each possible path according to the criteria listed
above. Two paths are equivalent with regard to these criteria, if exactly the same aspects
apply. If two paths are equivalent, then the Dispatcher performs a random selection.
The criteria listed above do not prevent a path from being selected. They lower
the chance of a path to be selected, though, but the Dispatcher might select a path,
which is affected by a negative criterion, if there is no “better” alternative.
Special attention should be paid to the distance to an appropriate destination block. If
the distances to appropriate destination blocks of two alternative paths are different,
then the Dispatcher will probably select the shorter path. If the shorter path is currently
locked by an obstacle, then it depends on the difference of these distances, whether the
Dispatcher uses the longer path or decides to try to pass through the shorter path in the
hope, that the obstacle disappears soon. In other words: the Dispatcher does not select a
free path under all circumstances, especially not, if the free path is much longer than
other alternatives, that are currently not available.
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