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Abstract
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Eight percent of the male population has color defective vision. It is felt that many of these individuals have difficulty recognizing colored traffic signals. The extent of the difficulty has not been investigated thoroughly under actual driving conditions. However, physiologists and physicists feel they can predict theoretically the number and type fo errors a color defective person will make.
Traffic signals commonly use a three color red-yellow-green signal. It is felt that the color defective driver recognizes traffic signals by the positions of the color in a constant order - usually red on top and green at the bottom. He also uses movement of other traffic and difference in brightness between colors as secondary clues of recognition. These clues are not always present as traffic signals are not always standard even in the same city and in many cases they are placed horizontally. The positions may not be possible to assess because in certain circumstances one sees only the illuminated signal. Also, there may not be any visible moving traffic.
Most authorities agree that under artificial conditions, when color is the only clue, the color defective makes numerous mistakes. Judd and later Sloan experimenting on a red, green and blue signal system, came to the same conclusion. In a more recent experiment Nathan et al showed that color defectives were slower in recognizing colors and made more errors than normal.
Field studies seem to indicate that in comparison, few mistakes are made by the color defective in actual driving. One such study performed in England on bus drivers, showed that the color defective had no more accidents with traffic signals than the color normal. Another field study by Gromberg- Danielson on drivers of all categories showed that neither the protan (red defective) nor the deutan (green defective) had any more tendency to confuse the traffic signals than a normal control group. The protans, however, were prone to overlook red and red-orange signal lights. Such individuals had more accidents by bumping into the rear of a preceding car.
In 1964, the indicator lights on the front of the new cars were changed from a white to amber colour. The change from white to amber light was made on the assumption that the addition of red makes a light more readily visible. That well known fact holds true for a colour normal person but is it true for a colour defective person? The present investigation was then devised to check the response of colour defective individuals to five different coloured flashing light signals - red, green, blue, white and amber. In addition, their response to the standard red, green and yellow street traffic lights was studied. The same subjects were then tested on "Symboliite" traffic signals, a new signal system incorporating a new dimension, i.e. the use of a different shape for each coloured signal. |