an electricity supply may not be readily available at all of these junctions, particularly those in rural areas, but we think that as soon as possible electricity should be provided for them.
It should be left to the discretion of highway authorities to decide whether directional signs as well as other important signs be externally or internally illuminated. We are aware of recent developments in the design of box type internally illuminated signs for commercial purposes and we think that there is a use for this type in the traffic sign field.
As many informatory signs in lighted urban areas do not justify the expense of direct lighting (e.g. toilet and parking signs), these should be placed where they are made visible after dark by street lighting.
As regards temporary signs, all mandatory, prohibitory and warning signs, and most informatory signs, should be reflectorised. But we recognise that where temporary warning and informatory signs are used for a very short period, for instance for local special events, it might involve unreasonable expense to reflectorise them unless they are important to safety. Such unreflectorised signs should be placed so that they catch as much light as possible.
260. Button type reflecting lenses have been commonly used to illuminate the characters and symbols of traffic signs . But these have been largely superseded by beaded reflecting material applied to the sign background so that its characters and symbols are seen in dark contrast against it. In our view, reflecting material is greatly superior to reflecting lenses for this purpose. Reflecting material should be used for the background illumination of all black on white directional signs other than those which are directly lit. We have made tests to determine whether reflecting material could effectively be confined to panelling the legends and bordering the route symbols of advance direction signs but we have found this to be unsatisfactory. We therefore recommend that whatever the size of a black on white sign the whole background should be reflectorised.
261. British Standard No. 873 : 1959 'The Construction of Road Traffic Signs and Internally Illuminated Bollards' specifies the requirements for external lighting lanterns for the direct illumination of traffic signs. It also recommends the number of lamps and their ratings for different sizes of sign. As regards the photometric performance of the lanterns the standard specifies that the light distribution shall be such that when the lantern is mounted with the appropriate sign the average luminance of the white parts of the sign shall be between 4 and 10 candelas per sq. ft. and the maximum luminance shall not exceed 30 candelas per sq. ft. Maximum values of luminance variation are also specified ranging from 10 : 1 for a 2 × 2 ft. sign to 40 : 1 for a 6 × 6 ft. sign.
262. It seems to us that the external lighting at present provided is frequently far from adequate. There seem to be three possible reasons for this:
(i) the variation in luminance permitted in B.S. 873 is too wide;
(ii) the lighting lanterns fail to meet the photometric requirements of B.S. 873 ;
(iii) the signs and lighting equipment are inadequately maintained.
As regards (i) it has been represented to us that the limits for average luminance in the British Standard should be raised to cater for the illumination
requirements of signs in streets lighted to Group A standard or better. It has
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