A Project is a piece of work such as a new section of track, signalling renewal scheme, or an incident investigation.

In the RDT a Project must relate to a section of track and the system therefore requires both a start and end point. A Project will have one or more Journeys associated with it.

A Journey is a specific train encountering a specific set of trackside features in a Project. There may be several Journeys created for a given Project.

For example, it may be useful to run several types of train through a defined set of features for a given section of track. Each train type would constitute a different Journey.

Alternatively, it may be useful to run a train through several different signalling schemes in order to assess the effect. Again, each signalling scheme would constitute a different Journey.

You can see the legend for some of the most common symbols on the Signalling Charts page or use the Group Standard:

Symbols for Plans and Sketches used in Signalling Applications

You may also want to ask for guidance from Network Rail signalling engineers or the Ergonomics Team.

Ergonomics is the science of designing work to fit the worker, instead of making the person adapt to working conditions.

Ergonomics uses information about human abilities, attributes and limitations, and uses methods and techniques to investigate and predict people’s behaviour at work.

This ensures that work systems are designed, implemented and operated to minimise mis-matches between what a person is mentally and physically able to do, and what is being expected of them.

The result is a healthier, happier workforce, and a safer, more reliable railway.

There are a number of theories of how human process information:

Wickens’ Multiple Resource Theory (MRT)

The MRT proposes that the human operator does not have one single information processing source that can be tapped, but several different pools of resources that can be tapped simultaneously. Each box in the diagram below indicates one cognitive resource. Depending on the nature of the task, these resources may have to process information sequentially if the different tasks require the same pool of resources, or can be processed in parallel if the task requires different resources.

Wickens’ theory views performance decrement as a shortage of these different resources and describes humans as having limited capability for processing information. Cognitive resources are limited and a supply and demand problem occurs when the individual performs two or more tasks that require a single resource (as indicated by one box on the diagram).

Excess workload caused by a task using the same resource can cause problems and result in errors or slower task performance. For example, if the task is to observe a speed board then no excess demands are being placed on any one component. However, if another task is being performed at the same time that makes demands on the same component(s), the result may be excess workload.

The relationship between workload and performance is complex. It is not always the case that as workload increases performance decreases. Performance can be affected by workload being too high or too low (Nachreiner, 1995). Sustained low workload (underload) can lead to boredom, loss of situation awareness and reduced alertness. Also as workload increases performance may not decrease as the operator may have a strategy for handling task demands.

Wickens’ theory allows system designers to predict when:

• Tasks can be performed concurrently.
• Tasks will interfere with each other.
• Increases in the difficulty of one task will result in a loss of performance of another task.

The VCAP model

McCracken and Aldrich like Wickens, describe processing not as one central resource but several processing resources: visual, cognitive, auditory, and psychomotor (VCAP). All tasks can be decomposed into these components.

• The visual and auditory components are external stimuli that are attended to.
• The cognitive component describes the level of information processing required.
• The psychomotor component describes the physical actions required.

They developed rating scales for each of the VCAP components, which provide a relative rating of the degree to which each resource component is used.

Joseph Hopkins’ Theory

Joseph Hopkins developed a training methodology, where the background to his training theory is that complex skills are, in essence, resource conflicts where training has removed or reduced the conflicting workload demands, either by higher level processing or by predictive time sequencing.

The theory postulates that the training allows the different task functions to be integrated into one new skill. An example of this is learning to drive a car. Changing gear and steering are two conflicting tasks (i.e. both require the same resources) before they are integrated into the new skill of “driving”.

An experienced driver will not need to think about what to do when turning a corner (higher level processing) or alternatively may change gear earlier than required to give sufficient resources for steering round the corner (predictive time sequencing).

The RDT will not tell you how to design an infrastructure layout. However, it will allow you to evaluate various layout options early on in the design stages in terms of how the design might impact on the driver’s workload.

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Using the RDT can give designers, engineers and investigators a valuable insight into the train driver’s experience of the track lay-out.

By understanding how design impacts on the driver we can build infrastructure that is easier to drive.

The RDT provides a framework for examining the behavioural aspect of train driving incidents that is not available for investigators through any other tool or technique. The RDT offers:

• A means for modelling the train’s approach to a signal and the activities that a driver would have to complete
• A framework for tracing, identifying and mitigating mechanisms for driver error in approach under investigation
• A set of behavioural model that indicate if workload may be excessive in the approach under investigation

The OTMR data is not necessary for using the RDT for incident investigation – it simply offers additional insight into the investigation.

The key data for the analysis are:

• The incident report which gives you details of the events, and also describes the normal operations over the infrastructure that should be taken into account in the analysis
• The infrastructure arrangement related to the incident (which you can get from the signalling design diagram)