Visual Performance for Motorists

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Visual Performance for Motorists

van Bommel, Wout

A motorist’s visual performance can be assessed using a number of different performance criteria. The visibility of static objects (obstacles) and dynamic objects (other road users, including pedestrians) and the visibility of changes in the visual scene and the detection of relative movement are examples of important criteria. Detection just on the threshold of visibility is often not enough for safe driving: good supra-threshold visibility increases the chance of a motorist reacting in time. Another aspect, important for decreasing reaction time, is peripheral vision: noticing something out of the corner of the eye, “off” the line of sight, that needs attention. As will be explained in this chapter, peripheral vision is different in the mesopic vision range as compared to the photopic vision range.

In order to be able to draw conclusions as to what lighting quality is needed under different situations, the individual relationships between photometric lighting parameters and the different performance criteria, such as revealing power, total revealing power, visibility level, small target visibility and relative visual performance, have to be studied. Fortunately, there are many research results on the relationships between the most important performance criteria and the various lighting parameters. These will be dealt with here. The impact of adverse weather conditions and of the effect of vehicle lighting on the visual quality obtained from fixed road lighting, are other items dealt with here. Finally, the neurological influence that lighting could possibly have in helping to keep the motorist alert will be discussed.