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Home 9 Human Performance 9 Category: Vigilance and distraction

Vigilance and distraction

About this topic


The term vigilance refers to a state of focused and sustained attention and concentration. It can impact human performance, particularly where systems rely on human intervention to keep them operating and to intervene when threats or errors arise. How well a person can remain vigilant is dependent on many factors, including the level of cognitive demand, the duration of the task, the level of arousal (which may be impacted by fatigue or reduced task novelty/stimulation), or when competing tasks or stimuli are introduced – as may occur through distraction.  

Distraction occurs when attention is diverted from a primary task, reducing a person’s ability to focus and impairing their level of vigilance. It is typically caused by a relative lack of interest in the primary task, an inability to sustain attention over time, or the intensity of the distractor (particularly if it is novel, attractive or attention grabbing). For example, maintaining attention to a monitoring task, like watching a screen where there has been no change for a long period of time, can be difficult when a person is feeling tired or if there is movement and noise on an adjacent display. A distraction can be external (e.g. movement, light, noise) or internal (e.g. fatigue, hunger, illness or rumination). 

Relevance to Rail

Vigilance is a characteristic particularly required of rail employees undertaking safety critical activities like driving a train, carrying out signalling or electrical control operations, monitoring and managing network performance and undertaking maintenance and inspection activities. We rely on people’s vigilance as a risk control, anticipating that when they are performing at peak vigilance they will identify and react swiftly to threats and errors (a red signal aspect, a trespasser on the track, the communication of incorrect information, an alarm) in sufficient time to prevent an adverse outcome.  Impairment to vigilance, including through distraction, can lead to operator or maintainer error and can result in poor safety and performance outcomes.  

Similarly, we rely on the vigilance of people to help them remain safe when in proximity to the rail network. Train platforms and level/pedestrian crossings have been the source of injury and fatality for rail employees as well as the public due to poor vigilance, including through distractions such as mobile devices or engagement in other tasks when people should be looking out for approaching trains.  Many rail safety campaigns have focused on highlighting the need to maintain vigilance and reduce the risk of distraction at the train-person interface to help reduce the risk to safety.  

While we can design systems and work environments to help enhance user vigilance and reduce the opportunity for distraction, it’s not reasonable to expect people to be vigilant 100% of the time. Design needs to account for risk associated with reduced vigilance and ensure there are additional controls in place to maintain safety, not just a reliance on user cognition and behaviour. 

With a transition to increased automation in rail operations, vigilance has become a focus of a lot of human factors analysis. For example, automating operational tasks that might otherwise have been performed by a train driver means a shift in operator activities, with more monitoring and less active control of the train. The risk of reduced stimulation for the driver as they operate the train can impact their vigilance and therefore their reliability as a risk control. The introduction of new technologies can also introduce distraction for operators from their primary tasks. Designers and engineers can work with HOF professionals to look for ways to mitigate opportunity for error (in this case, a driver failing to observe and react to a threat), such as by introducing secondary tasks aimed at maintaining driver engagement (additional checks, memory tasks, use of risk-triggered commentary), or through providing additional engineering controls (speed proving, train stops, alarms, vigilance systems).  Even with these controls, humans can still be vulnerable to distraction impairing vigilance.  Operator vigilance on its own will not be a reliable control, and additional layers of defense will be required to reduce the risk of error and adverse safety outcomes. 

Approaches and Methods

Human-centred design is the most effective way of designing to maintain human performance and mitigate against the risks associated with impaired vigilance and distraction. This is important not just for the design of systems and technology, but also in the design and scheduling of work – such as by reducing time on task for activities with high (or very low) cognitive workload, by task rotation and by ensuring a good person-job fit. 

The use of train driver vigilance devices is one way rail companies have attempted to monitor and manage the risk of reduced driver vigilance. Vigilance control systems verify that the driver is not incapacitated by monitoring task-linked activities and applying the train’s brakes if that activity is not performed.  

Vigilance, and impairment to vigilance such as through distraction, can be assessed through targeted analysis measuring performance through detection of or reaction to stimulus, often combined with tasks aimed at increasing workload or introducing distraction to see how vigilance is impacted in the face of competing demands.  Testing can occur using simulators or through the simulation of actual work scenarios. The Psychomotor Vigilance Test (PVT) is one common tool utilized to test sustained attention in the workplace.  Eye Tracking tools have also been used to test for distraction from primary visual tasks.


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