Road Network Operations
& Intelligent Transport Systems
A guide for practitioners!

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Human Performance

Human performance describes how easily and efficiently an individual achieves a certain outcome – such as navigating to an address, crossing the road or buying a bus ticket.

Human performance is based on a physical and cognitive (mental) control “system” that is the result of millions of years of evolution. Human action is largely effective and adaptive even when carrying out complex tasks – but humans are not machines – whatever role they are undertaking. It is important to understand the limits and the variability of human performance so that transport systems and ITS can be designed and operated accordingly. Performance varies between people and an individual’s performance also varies depending on a complex interplay of factors. These variations can make or break the success of new applications of ITS, such as cooperative driving. (See Coordinated Vehicle-Highway Systems)


People make errors! Sometimes it is useful to draw a distinction between “slips”, “lapses” and “mistakes”. Slips and lapses are skill-based errors. Slips occur when there is a mismatch between someone’s intention and action – intending to do the right thing but doing it incorrectly. These are often quickly realised and may be corrected. Lapses are when a user forgets to do something or their mind goes blank during a task. Mistakes, on the other hand, result from some misperception or misjudgement and are decision-making errors – doing the wrong thing but believing it to be right. These are often much harder for a user to identify and correct. We cannot predict exactly when errors will occur but there has been considerable research concerning their context and likelihood.


Performance is affected by specific impairments that people may have – these can be (semi-) permanent, such as a broken arm or colour-blindness or temporary. Examples of temporary impairment include tiredness – which is a particular issue for shift workers. Individuals can also be intoxicated or unwell which can affect their performance.


Human performance varies depending on arousal (excitation level). Individuals can be under-aroused (sleepy, dis-engaged) or over-aroused (excitable, anxious). Individuals perform at their best when at neither extreme.

Arousal/Performance curve


Performance often depends on motivation (See Motivation and Decision Making), which can also interact with arousal. Individuals tend to perform better when they are well-motivated.

Undertaking Single and Multiple Tasks

A control room operator using a terminal, or a public transport user reading dynamic signage, may concentrate on the terminal or the sign as a single focus of attention. This contrasts, for example, with a driver observing the road whilst simultaneously adjusting the car entertainment system. Sharing of attention between two tasks is known as the “dual task paradigm”. Performance when undertaking a single (or primary) task is usually better than when trying to undertake another (secondary) task at the same time – because mental resources have to be shared between the tasks.

Use of Physical and Cognitive Resources

It is well known that performance varies between individuals. Issues such as strength, reach, endurance and reaction time are examples of physical ergonomics which can be measured for different groups.

Human performance in the context of today’s increasingly technological transport systems also depends on an individual’s information processing capacity. To a large extent this is affected by how an individual’s various physical senses or “channels” – such as visual and auditory – handle the streams of information encountered. All channels require mental resources to process information and these channels can become overloaded. There is more interference within channels than across them. For example, talking whilst engaged in a control task is easier than operating two controls or holding two conversations simultaneously.

Research suggests that not all mental resources are equal and “multiple resource theory” accounts for how it is sometimes possible to do two things at once – as long as specific limited mental resources are not required for both tasks.

Training and Practice

Training can greatly affect performance through repetition, practice and familiarity. For example, a public transport user familiar with a ticket machine can make a purchase more quickly than an unfamiliar traveller. Some activities, such as the use of the clutch when driving, can become almost unconscious requiring very little effort. Performance generally increases with training although “overtraining” and complacency/boredom can become a negative factor in some cases.

Education allows individuals to form mental models of why and how things work and may therefore increase performance by reducing errors and increasing motivation.

Advice to Practitioners

Expect and allow for variability between people and for a variation in one person’s performance/ability at different times and in different circumstances. The variability may be obvious (such as age, size, physical disability) or may not be. Where possible, design for the least able and most endangered. (See Diversity of and user groups)

People make mistakes, so it is essential that ITS is designed so that systems and processes minimise the possibility of errors and provide opportunities to recover from them. (See  Automation and Human Factors). Task and error analysis may be helpful. (See Human Tasks and Errors). Particular care needs to be taken when an individual’s mistake could have safety consequences for themselves or other road users.

Road Users (drivers, PTW riders, cyclists, pedestrians)

Driving – and Powered Two-Wheeler (PTW) riding – is a complex and safety-critical task which requires physical and mental resources. Driving skill and performance can be improved through education and training. A minimum level of performance should be required at all times whilst driving. Drivers’ skills need to be tested, at least initially, and a minimum standard should be enforced. New technology can introduce tasks additional to driving, such as making a phone call – which can impair driving performance and should be discouraged on grounds of road safety.

Vulnerable road users – such as cyclists and pedestrians of all ages – will vary, for example, in the degree of their physical movement, direction-finding and road awareness. All information and directions aimed at them should be designed to be simple, unambiguous and easily perceived.

ITS Infrastructure Design – Promoting Performance

ITS infrastructure (including signs, payment facilities, speed limits) should be designed to take account of the intended user population and the variations in performance that they have. Many human factors standards and guidelines are available which are suited to different ITS applications. (See  HMI Standards and Guidelines). Using internationally agreed standards and guidelines for HMI is recommended – they help to promote familiarity and often provide multiple signals to the brain for recognition (for example, use of colour and shape).

When possible, new designs should be simulated and trialled with the intended user population to ensure that human performance shows that they can be easily understood and used. (See UK Smart Motorways  )

ITS infrastructure should also be designed to take account of the performance limitations of those personnel involved in their maintenance. (See Work Zones)

Public Transport Users

Public transport operators need to be mindful of the broad range of human performance and specific disabilities that may impair performance – when designing or purchasing systems such as display screens and ticketing facilities to: (See Diversity of Users)

  • provide information using a variety of channels (visual, auditory) to help users with information processing wherever possible
  • allow users to proceed at their own pace when interacting with ITS. This means that the technology should match the performance of the user (not vice-versa). If possible shortcuts should be provided for users familiar with equipment whose performance level may be substantially higher than unfamiliar users

Control Room Design and Operations

The Road Operator will need to set standards, provide training and undertake regular performance reviews of control room operators. (See Traffic Control Centres) They need to:

  • appreciate the broad range of human performance and specific disabilities that may impair performance when people interact with systems such as display screens or control inputs
  • try, if possible, when designing control room responsibilities and tasks, to vary activities to avoid boredom and keep the operators engaged. Human factors professionals can help design jobs and identify:
    • tasks that can be performed concurrently
    • tasks that will interfere with each other
    • where an increase in the difficulty of one task will result in a loss of performance on another task

Human factors professionals can assist in designing work and shift patterns to minimise performance degradation. (See Infrastructure)

Maintenance and Emergency Response Workers

The road should be considered a potentially hazardous working environment for personnel such as maintenance and emergency response workers. Road Operators should:

  • set standards, provide training and undertake regular performance reviews of on-road workers.

Human factors professionals can assist in designing work and shift patterns to minimise performance degradation.


Reference sources

Dewar, R. and Olson, P. (2002) Human Factors in Traffic Safety. Lawyers & Judges Publishing Company, Inc. ISBN 0-913875-47-3

Sanders, M. and McCormick, E. (1993) Human Factors in Engineering and Design. McGraw-Hill, Inc. ISBN 0-07-054901-X