Infrastructure

ITS is capable of presenting new and existing traffic information to road transport users in radically different ways from that of conventional traffic signs. Variable message signs can be implemented through a range of technologies. They can include text, pictograms and moving images with various colours. Other changeable signs, including those that display actual vehicle speed (and sometimes vehicle identification information), can be part of an ITS designed to influence driver behaviour with dynamic and targeted information. (See Use of VMS)

There is a broad range of new and developing signage systems involving ITS. For many of these, experience has yet to be developed into specific guidelines whereas relatively good information is available on Variable Message Signs (VMS).

Just as with conventional static signs, to be effective, VMS have to be noticed, understood and followed. These are human factor considerations primarily for drivers for which various guidelines exist on their design.

Conspicuity describes a sign’s prominence from a driver’s perspective. This depends on its optical properties such as luminance (amount of light entering the eye from the sign) and contrast ratio, as well as factors such as size and contrast with surroundings. The general advice is for high luminance and high contrast signs.

Legibility describes the extent to which sufficient detail is visible at a given distance. This also depends on whether it is necessary to read a shape or individual letters. Legibility is enhanced through large letters but there is a trade-off against message length and any sign size. The resolution also depends on the underlying technology (such as the size of the smallest individually controllable image element).

The limited time that drivers have to read a sign restricts their perception of the length and complexity of the message. Some “rules of thumb” exist concerning how many words can be read during different glance times. Well-designed pictograms can quickly communicate concepts and are not language-specific, for which some advice about their design and use is available.

Message comprehension is basically a human task of pattern recognition, and in assessing whether a VMS will be comprehensible it is important to understand:

• the exact message that the sign is intended to convey
• the context of use
• the user population

Relevant to the context of use, visual clutter in the driving environment has been extensively researched and shows that distractions in the visual scene reduce drivers’ performance when responding to signs. For example, advertisements, and particularly ones with dynamic images, can decrease the effectiveness of other signage.

Advice is available on a range of VMS design issues including message length, message formatting, mixing text and pictograms and using dual-language text. There is some evidence that blank VMS confuse drivers which suggests that it is probably best to always carry some message on a VMS, such as a road safety warning or – when available – current point-to-point journey times.

Advice also exists on how to measure comprehension and how to assess whether correct actions – that are timely, credible and appropriate – are taken.

Tunnels are an important feature of the road infrastructure and one where safety in their use is a crucial issue – because accidents in tunnels, and particularly fires, can have dramatic consequences. Two thirds of crashes happen at the portal areas but accidents inside the tunnel tend to be more serious. The key human factors issues seem to be related to lighting, lack of variation, and lack of landmarks to give any speed or distance references.

In long tunnels driver monotony and reduced concentration can be addressed through the design of lighting – for example by creating the impression of driving through several shorter tunnels by making transition zones using different lighting effects. Monotony can also be reduced by designing-in gentle curves and short straights (without breaching guidelines for safe viewing distance) (See Mont Blanc Tunnel Management System).

Intelligent monitoring and control systems are frequently used for air quality temperature, water seepage, fire, radio connections, lightning systems, traffic lights, emergency equipment and many other critical functions – so that if faults or incidents occur, the tunnel can be automatically closed to traffic.

In the European Union a Directive describes minimum safety standards. Much of it relates to organisational and operational schemes for testing, inspecting, training and equipping the emergency services – rather than human factors design issues. A PIARC report is available that reviews user behaviour in road tunnels in both normal and critical situations and provides additional recommendations for tunnel design and operation based on human factors considerations. It also covers what can be expected in the future from ITS regarding improvement of safety in tunnels. In summary, the recommendations are to take greater account of human factors in road tunnel design, particularly concerning:

• better information about how drivers should behave
• a 150-200m lead in to the tunnel portal without visual clutter
• clear, simple and repeated signage
• easily recognisable safety provisions (even during normal operations)
• multiple-redundant alarm sources

Traffic control centres are an integral part of ITS – and the application of human factors considerations can play a pivotal role in increasing efficiency, productiveness, operator well-being and safety. It can also help to reduce the potential for, and consequences of, human error. Human factors issues in control centres include physical aspects (from the design of individual controls at operating stations to the building’s design and location) and procedural aspects (such as staffing and shift scheduling). (See Traffic Control Centres)

In terms of the physical ergonomics, a suite of international standards (under the umbrella of BS EN ISO 11064) is available that deal specifically with the ergonomic design of control centres. There is also an extensive suite of standards (under the umbrella of BS EN ISO 9241) that deals more generally with the ergonomic requirements for office work with visual display terminals (VDTs) and the ergonomics of human-system interaction.

Many control centres will need to operate around the clock and so may use a shift work policy. This can have negative effects on personnel if not implemented correctly. Employers must consider the workload, the work activity, shift timing and duration, direction of rotation and the number/length of breaks during and between shifts. The UK Health and Safety Executive has produced a book that provides practical advice on implementing and managing shift work.

Good Practice Guidelines for Shift Design

• plan an appropriate and varied workload
• offer a choice of permanent or rotating shifts and try to avoid permanent night shifts
• either rotate shifts every 2-3 days or every 3-4 weeks - otherwise adopt forward rotating shifts
• avoid early morning starts and try to fit shift times in with the availability of public transport
• limit shifts to 12 hours including overtime, or to 8 hours if they are night shifts and/or the work is demanding, monotonous, dangerous and/or safety critical
• encourage workers to take regular breaks and allow some choice as to when they are taken
• consider the needs of vulnerable workers, such as young or ageing workers and new and expectant mothers
• limit consecutive work days to a maximum of 5 - 7 days and restrict long shifts, night shifts and early morning shifts to 2-3 consecutive shifts
• allow 2 nights full sleep when switching from day to night shifts and vice versa
• build regular free weekends into the shift schedule

Good Practice Guidelines for the Work Environment

• provide similar facilities as those available during daytime and allow shift workers time for training and development
• ensure temperature and lighting is appropriate and preferably adjustable
• provide training and information on the risks of shift work and ensure supervisors and management can recognise problems
• consider increasing supervision during periods of low alertness
• control overtime, shift swapping and on-call duties and discourage workers from taking second jobs
• set standards and allow time for communication at shift handovers
• encourage interaction between workers and provide a means of contact for lone workers
• encourage workers to tell their GPs that they are shift workers and provide free health assessments for night workers
• ensure the workplace and surroundings are well lit, safe and secure

Further Information

ISO 11064:

• 1:2001: Principles for the design of control centres.
• 2:2001: Principles for the arrangement of control suites.
• 3:2000: Control room layout.
• 4:2004: Layout and dimensions of workstations.
• 5:2008: Displays and controls.
• 6:2005: Environmental requirements for control centres.
• 7:2006: Principles for the evaluation of control centres.
• ISO/IEC. 1998: 9241–11. Ergonomic requirements for office work with visual display terminals (VDT)s – Part 11 Guidance on usability, ISO/IEC 9241-11: 1998 (E), 1998.