Track Movement Sequencing Logic
Track Movement Sequencing Logic
A dynamic network model strives for realism. It must strike a balance between the provision of enough traffic management rules to reduce the probability of deadlocks, and the provision of so many rules that the traffic-carrying capability of the system becomes unrealistically low.
The Planimate® Platform contains logic for controlling train item movement around a track network. The underlying philosophy is to aim for simplicity and to provide modellers with immediate traffic management over a network without them having to first design any movement rules of their own.
By design, the logic does not optimise localised train movement scheduling, nor does it perform overall system-wide trade-offs. Train Item movements are resolved on a first come first served basis and the Platform manages what it is presented with locally.
In the case of simultaneous competition for a section, the train item with the highest ‘priority’ wins out, depending upon the circumstance. In conditions of “moderate congestion”, the movement logic may "relax" priority-based assignments in the interests of moving trains through the system to ease the congestion and release capacity.
However if you move trains into a track network, assigning trains to sections, roads and loops using simple rules to avoid ‘collisions’, you end up with a deadlock in short order. The issue of deadlock limits how simple you can make the rule set with which train item movements over a network are managed.
The rules that guide train item movement decisions have to respond to the wider “network context” within which each train item’s movement is contemplated. Each decision requires knowledge of where other relevant train items are in the network and where they are heading. Some movements will increase the chance of deadlock developing more than others.
Making movement decisions by taking full account of the position and routing for every train on even a simple network consumes huge memory and processing resources. The Planimate® Platform avoids this overhead by adopting a general rule set designed guide decision-making about moving each train item individually, given the “network context” within which it finds itself.
In order to reduce the chance of a deadlock occurring, the Planimate® Platform uses rules developed to favor train item movements that tend not to constrain the movements of other train items. Of the many possible ‘next movements’ in a network, given the specifics of network occupancy at that time, some will not comply with these general rules regarding train movements toward, and be disallowed.
During a simulation run, the rules in this logic pursue a balance between these basic goals:
- To facilitate reasonable sequencing of train item movements over the network,
And at the same time… - To avoid train item movements that increase the chance of a “deadlock” occurring.