Optometry and Vision Sciences - Theses
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ItemAn analysis of colour vision standards in the transport industry( 1984)Colour vision standards were introduced by transport industries at the end of the nineteenth century. They have remained relatively unchanged since introduction, despite advances in transport technology and improved knowledge on the characteristics of human colour vision. No agreement exists on the precise level of rigour that standards should set, or if they are needed at all, which has led to an inconsistent diversity of standards used by many transport authorities. This thesis reports a critical analysis of the use of colour coding within the transport industry and concludes that colour still serves an important role in information transfer, despite an increasing reliance on electronic aids for navigation and communications. Disabilities suffered by colour defective observers identifying colour codes are also reviewed. Experimental studies reported in the literature show persons with abnormal colour vision are more likely to make colour confusions, have slower reaction times and reduced visual ranges to coloured signal lights. Accident statistics suggest certain colour defective groups may have a higher risk of accident than persons with normal colour vision. Thus it is concluded that standards of colour vision remain justified and should be retained, especially for operators of public transport vehicles. Experiments conducted and reported in this thesis consider problems specifically related to certain types of colour defective observer or the testing of colour vision. Protanomals and protanopes were found to have a similar reduction of visual range to deep red colours, even though protanomals possess a red-absorbing cone photopigment. Therefore protans should not be considered safe for employment where distant signals, especially red signals, must be recognized. The history of tests used for enforcement of colour vision standards is reviewed. Lantern tests, introduced in 1875, remain the principal test methods for the administration of colour vision standards. It is argued that lantern testing should continue because clinical tests poorly predict an observer's ability to recognize coloured signal lights. However, protanomals pass some lanterns and a clinical diagnosis should supplement these lantern tests to identify and reject protans. Ergonomic solutions, in the selection of colours, do not help colour defective observers reliably recognize a red-green-white colour code, even after allowing an extended practice trial at the recognition of these colours. Protanopes show least benefits from these engineering changes and give the worst performance. However, colour identification by other observer groups improves using a bluish-green or deeper red than the present orange limit recommended by the CIE. Finally, a rational approach is suggested for setting colour vision standards by transport authorities. This approach considers the variables of task demand, exposure, consequences of accident and community attitudes. It suggests international implementation of a set of equitable standards based upon these factors, rather than loosely or poorly defined standards that may be subject to various interpretations. Three classes of standard are recommended, namely, colour safe, colour normal and colour defective safe. These classes define the intent of the standard with each recommended fail criterion establishing the degree of difficulty set.