The show must go on

Ricardo Saldanha, Head of Innovation,  @SISCOG  |  7 min read 

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Who hasn't experienced the need to change plans because some unexpected event forced things to go in another direction? This is exactly what happens every day in train operation.

In railroad or subway operation, trains run over a network according to a highly detailed plan that specifies how resources (track, rolling stock, and crew) are used in each minute of the day, sometimes in each fraction of minute. The reason for this is to make sure that the right number of resources are available at the right time and location and that these resources are used efficiently.

Disruptions and how to cope with them

Unfortunately, during the day many unexpected events prevent the train operation to run as planned.

These events are called disruptions, and they can vary in scale:

• Small perturbances, such as departure delays due to overcrowded stations, mechanical problems that force trains to run at a lower speed, or crew members signing in late;
• Medium disruptions, such as engine breakdowns in station yards or a crew members falling ill;
• Large disruptions, such as forced stops of trains on the main line, extreme weather events, run overs, derailments, or collisions.

When these disruptions occur, actions are taken aiming at the following goals:

a) keep passengers and crew safe (first priority);

b) keep trains running as smoothly as possible (second priority).

For a), and partly b), railroad companies have rescue brigades at several locations across the network, specifically prepared to act on accidents. Their mission is to save lives first, and then to clear the track as rapidly as possible so that trains can resume operation.

For b), these companies also have dispatching centres at several locations along the network. Their mission is to rapidly adjust the operational plan to accommodate the new unexpected conditions and, when those conditions no longer apply, make the necessary adjustments to return to the original operational plan. They also have to communicate these adjustments to the crew members who will execute the plan.

When disruptions occur, the first priority is to keep passengers and crew safe, and the second is to keep trains running as smoothly as possible.

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Disruption management process

Dispatching centres have several dispatcher teams that cooperate with each other.

In large incidents, the first that are called to action are the traffic controllers. They work for the infrastructure manager and are responsible for making high-level adjustments to the timetable. They communicate these adjustments to the signallers and the operation controllers.

The signallers also work for the infrastructure manager. They are responsible for making low-level adjustments to the timetable and communicating them to the operation controllers.

The operation controllers work for railroad undertakers. The rolling stock operation controllers make the necessary adjustments to the rolling stock operational plan and communicate them to the crew operation controllers, who then adjust the crew operational plan and communicate the changes made by all dispatchers to the crew members.

There are also staff whose job is to inform the passengers of timetable changes, in addition to any passenger information systems in place, and to arrange bus bridging services to allow passengers reach parts of the network that cannot be temporarily reached by train.

Figure 1 describes the workflow of a dispatching centre.

Figure 1: Typical workflow of a railroad dispatching centre.

Emergency scenarios

Dispatchers often use emergency pre-defined scenarios to speed up and improve the quality of their response to disruptions.

These scenarios describe what to do in response to specific types of disruptions. For instance, "if network section X gets blocked in both directions:

a) southbound trains short turn at station A, while northbound trains short turn at station B;

b) arrange a bus bridge service from A to B, etc.

Emergency scenarios typically cover the most common situations and should be regarded as a pattern that must be adapted to the specific case. They can describe the response to the disruption in a more or less detailed way. This means that they can bring more or less added value to the dispatchers. For instance, emergency scenarios tend not to be of great help to crew operation controllers because crew plans are much more irregular than the other plans, which makes it almost impossible to develop standard responses to complex disruptions.

An example of disruption management

Figure 2 shows an example of how traffic controllers handle a situation where a track section between stations B and C becomes blocked on both directions during a period of time represented by the pink rectangle.

The horizontal (vertical) axis of the time-space diagram represents time (distance measured along a line containing stations A, B, C and D). As shown, downward (upward) orange trains short turn on station A (D), while downward (upward) blue trains short turn on station B (C). After signalling controllers introduce low-level timetable changes (based on the decisions of the traffic controllers), rolling stock operation controllers are called to make the necessary adjustments on the rolling stock plan in addition to the adjustments made by the traffic controllers.

In the scenario shown in Figure 2, they have to attach additional train units on the fourth downward orange train, as well as to the fourth upward orange and blue trains. They also have to solve rolling stock imbalances created by the decisions of the traffic controllers.

Figure 2: Time-space diagram showing adjustments made by traffic controllers to handle a situation where a track section between stations B and C becomes blocked for a certain period of time.

Once rolling stock operation controllers finish their job, crew operation controllers take the lead to adjust the plans of train engineers and conductors. They must act quickly because they have to communicate the adjustments made by all controllers to the crew members who are responsible for executing them. In the example shown in Figure 2 they have to decide if crew members follow the rolling stock or not. That depends on how close they are to sign out time. If they are too close, they cannot be rerouted, and maybe the only solution is for them to take a taxi and go home. But then a second crew member is needed to perform the train after the short turn. Even if they can follow the rolling stock, controllers must ensure they return to base before they are planned to sign out. This may require making many changes to the crew plans.

Once crew plans are adjusted, the adjustments made by all controllers have to be communicated to all crew members involved. If some crew member cannot be reached because of a communication problem, another iteration of crew dispatching has to be performed, and so forth, until all crew members receive the information.

After all controllers completed their task, they might be informed that the disruption ending time is earlier or later than expected. Then, another round of the workflow shown in Figure 1 is initiated. This process may occur several times until the disruption really ends.

This is why decision support systems equipped with optimizers are necessary.

Decision support systems equipped with optimizer

In order to allow dispatchers to make good decisions in a very short time frame, they need tools (like the one shown in Figure 3) that provide decision support at various levels, namely:

• Monitor and provide a global view of the operation, receiving information about events (e.g. train delays, rolling stock breakdowns, and staff unavailability) in real-time, and representing their impact on resource utilisation plans
• Quickly make the necessary adjustments on resource utilisation plans in case of a disruption, either manually or automatically, while complying with all preferences and operational rules
• Easily identify open work, and allocated and available resources, as well as their location, using filtering and colour coding
• With the use of a timeline, see the tasks that are being performed and are about to start
• Provide last-minute notifications to staff

Figure 3: Example of a decision support system for crew disruption management.

Decision support systems can lead to more efficient rescheduling solutions: less cancelled or delayed train trips, maintenance costs, energy consumption, and staff extra hours.

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Specially in medium and large disruptions, the use of optimizers may play a very important role. In extreme situations, such as several large disruptions at the same time, they can be the only solution for dispatchers not to lose control of the operation. They can also lead to more efficient rescheduling solutions, which result in less cancelled or delayed train trips, maintenance costs, energy consumption, and staff extra hours.

Further reading

The following references provide more useful information about decision support for disruption management:

• P.-J. Fioole, D. Huisman, G. Maróti, and R. L. Saldanha, Reduced (winter) timetable in the Netherlands: Process, Mathematical Models and Algorithms, Proceedings of the 12th World Congress of Railway Research, Tokyo, 2019
• E. Morgado and J. P. Martins. Automated real-time dispatching support. In Proceedings of APTA's Rail Conference, Dallas, 2012
• R. L. Saldanha, A. Frazão, J. P. Martins, and E. Morgado. Managing Operations in Real-time. WIT Transactions on The Built Environment, Vol 127 pp. 521-531, 2012