TRAFFIC SIGNAL LIGHTS

Southland Times, Issue 23182, 24 April 1937, Page 20

TRAFFIC SIGNAL LIGHTS

NEED FOR UNIFORM COLOURS Uniform international practice in the use of standarc’ colours for traffic signals came one step nearer realization when the 1935 conference of the International Commission on Illumination, held in Germany, adopted specifications for the colour of road traffic signals very similar to those approved by* the American Standards Association in 1927. The United States was the first country to have a standard specification on this subject. When the Sectional Committee on Colours for Traffic Signals started its work, various colours were used in the United States for traffic control purposes. In some places as many as 15 different colours or combinations of colours were being used to direct traffic. The choice of colours was frequently diametrically opposed to our present colours. In Chicago, for instance, green was being used on stop and go signs to indicate stop, whereas in railroad practice and in many other places green signified “go-ahead.” Not only were red, green, and yellow used for signal lights, but blue, purple, orange, were also to be found. Research Programme Finding such a variety of practice, the committee undertook a far-reach-ing research programme. They found that a red light of 75 candle-power, with an average daylight landscape background, i ould be identified at a distance of 600 feet, whereas a green light had to be 250 candle-power, a yellow light 750, and a blue light 1000 candle-power to be identified at the same distance, It was also found that some colours penetrate fog and smoke better than others. Red and orange, for instance penetrate fog most easily, although green becomes invisible most quickly in fog. . . Because of the greater general visibility of red and green, and because red was found to be popularly associated in the public mind with the idea of danger, the commitee agreed upon the present traffic-light colour scheme —red, stop; green, go; yellow or amber, warning. The research which led to the decision to make red, green and yellow the standard colours for traffic lights also took into consideration the effect of colours on those who are col-our-blind. Approximately four per cent, of the entire population, or nearly 5,000,000 people, it was found, are colour-blind to some extent. _ The greater number of these have difficulty in distinguishing between green and red, but do not have difficulty in distinguishing blue and red. Therefore, the exact shades of red, green, and yellow were specified. In order that most colour-plind people can see the change from red to green lights, the green specified in the standard is what is known as admirality green, and verges very closely on blue. Recently, it has been held by some of those interested in the safty problem that persons who are colourblind should not be allowed to drive. Such may be the case if the provisions of the standard are not followed carefully, but if the colours specified in the American standard are used, only in rare cases will a colour-blind person have trouble in distinguishing the lights. Because of the difficulty of educating motorists to drive carefully and intelligently, it is increasingly evident that every mechanical device which can be provided must be used to the maximum of its efficiency.