whole, and experiments made in this country[1] support the view that light letters on a black or sufficiently dark ground are more legible than black letters on a white ground, particularly at night when the sign is illuminated by lights or reflective material. We therefore recommend the use of a dark ground in all signs relating to the motorways . This has the further advantage of enabling a distinction to be drawn between signposting on or relating to the motorways and signposting, on and relating solely to all-purpose roads, and so of giving an indication to a driver that he is approaching a motorway.
23. We rejected black as the dark colour for the background of motorway direction signs as being too negative in character, and red because it is reserved for danger signs . We finally reduced the field of choice to green (which has been adopted for direction signs on the Interstate Highways of America), blue (which is used on motorway signs for instance throughout Belgium, Holland and North-West Germany) and grey. During our visit to these European countries we observed that, despite the height of the signs, they were mostly seen against the natural greens of grass and trees, which, had the signs been green according to American practice, would have tended to reduce their target value. Apart from this, however, we think that there is in any case advantage in following European rather than American practice. Having thus established the claim of blue in preference to green, we carried out a practical, full-scale comparison between signs using a blue background and signs using grey. Taking both day and night conditions into account, the most satisfactory results were achieved with a blue background, and we therefore recommend the adoption of blue as the background colour for almost[2] all the motorway signs in this country. The particular shade of blue we recommend is the 'Standard Interstate Blue Colour', which is used on certain signs on the Interstate Highways of America and which is illustrated in the American Association of State Highway Officials ' Manual for Signing and Pavement Marking of the National System of Interstate and Defence Highways, 1958. This is the colour employed on the signs on the Preston By- Pass, where we have observed that it tells well against various landscape backgrounds without being unduly obtrusive.
24. The backs of the signs, on the other hand, should naturally be as unobtrusive as possible . We recommend the use of colour No. 4-051 of British Standards Specification 2660 of 1955. This is dark grey-green, which we believe will harmonise satisfactorily with the varied motorway backgrounds.
Illumination
25. We have had two demonstrations, arranged by the Road Research Laboratory, of floodlighting of large signs and were able to compare the legibility of these signs, both by day and night and at the speeds which are possible on the motorways, with that of similar signs dependent only on reflecting materials . We have no doubt that the most satisfactory results are achieved by electric lighting specially provided for the purpose, and we strongly recommend that
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