Page:Report of the Departmental Committee on Traffic Signs (1946).djvu/24

 Illumination of traffic signs

24. By night the conspicuity and legibility of all traffic signs should approach as nearly as possible to daylight standards. This is particularly necessary in the case of warning, prohibitory and mandatory signs.

We recommend that, where a system of street lighting exists, direct illumina- tion should be provided. It would be undesirable to discourage experiment and improvement in the illumination of signs by restricting the methods by which a satisfactory standard of illumination is achieved, but it is our view that where conditions permit of its use, external illumination is to be preferred to internal illumination because of the better daytime performance and greater simplicity and ease of maintenance of the externally illuminated sign.

On roads where there is no system of street lighting and vehicles normally drive with headlamps on, the use of reflecting lenses is, in the absence of direct illumination of the signs, a satisfactory method of rendering signs conspicuous and legible at night, provided the signs are properly sited in relation to the carriageway. We recommend that, on unlighted roads, all warning, prohibitory and mandatory signs for which direct illumination is not practicable should be fitted with reflecting lenses. As these lenses depend for their effect on the reflection of light directed on them from the lamps of approaching vehicles, they serve no useful purpose in signs erected on roads where there is an effective street lighting system and where vehicle headlamps are therefore not used.

Brightness of illuminated signs

25. Laboratory investigations carried out at our request suggest that a sign brightness of from 15 to 20 equivalent foot-candles will give adequate conspicuity and legibility on well-lighted streets, and at the same time will not cause discomfort or glare in unlighted or poorly lighted streets. We recommend that these results should be checked by full-scale street tests, including tests in brightly lighted shopping streets, as soon as conditions permit, and that appropriate recommendations should subsequently be issued to highway authorities.

The legibility of illuminated signs may be impaired by lack of uniformity of brightness over the area of the sign. This can be remedied by careful design and by the use of materials of appropriate quality.

We recommend that, as and when standard specifications for traffic signs are prepared or revised by the British Standards Institution, consideration should be given to such questions affecting illumination as the quality of diffusing or reflecting materials and the desirable intensity and correct location of sources of light in relation to the area illuminated.

Reflecting lenses in traffic signs

26. British Standard Specification for the Construction of Road Traffic Signs (Cast Metal) and Posts (No. 873—1939) specified the number, diameter and colour of reflecting lenses which should be used in certain authorised signs. The specification stated, however, that certain of the symbol warning signs “do not lend themselves readily to the fitting of reflectors” and, therefore, did not specify how reflecting Ienses should be used on these particular signs. We consider it important that the symbols to be used on warning signs should be capable of being fitted with reflectors, and we therefore caused experiments to be made to determine what amendments in the design of symbols would be necessary to enable this to be done. In our view it is sufficient for the reflecting lenses to outline at night a symbol which is distinct from other symbols, but they need not necessarily reproduce the exact detail of the black on white symbol as seen by day; e.g. the “Roundabout” symbol shows by