TRAFFIC SIGNS
Page 39
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TRAFFIC signs were the subject of 'an
I informal discussion held recently -by the Traffic Engineering Group of the Institution of Civil Engineers. Mr. R. L. Moore of the Road Research Laboratory introduced this topical and controversial subject.
It was emphasized that, ideally, direction signs should enable a newcomer to receive all the information that a regular road user had acquired by experience. This ideal state of affairs does not exist.
In considering sign revision, -certain .principles could be laid down which, though they could not always be adhered to in practice, helped to determine the placing and size of lettering and symbols on a sign. These were:
(1) The driver's act of reading the sign should not require him to slow down or distract his attention unduly from the task of driving safely in prevailing traffic conditions.
(2) A traffic sign should be perceived and understood by a driver travelling at the average speed of traffic on the road sufficiently early for him to take any necessary action with safety.
(3) The sign should fulfil the above conditions by night and day.
It was stressed that these principles did not lead immediately to a prescription for signs. No standard driver could be used as a yardstick. Estimates had to be made of what was normal vision. It was customary to take a reading distance for sign letters of 50 ft. per inch of letter height. Approximately 98 per cent. of drivers could accomplish this and this value was accepted both here and in America as being a reasonable one.
These letter sizes were arrived at for four-name signs on various types of road: Letter sizes for four name signs (in inches).
Place names on our present signs were small because it was the intention that motorists should navigate by route numbers. Reliance on route numbers alone, however, was hazardous. On turning on to A5, for example, there was only a 50 per cent. chance that one was on the way to Holyhead; one might just as easily be travelling to London. Some regular road users, it was mentioned, had a very hazy idea of the geography of the British Isles.
Bigger signs naturally cost more: doubling letter size made a sign nearly four times as expensive. Tests had therefore been carried out to find more economical layouts for direction signs than the present map-plus-route panels. There was much wasted space on this type of sign, but it was thought that more condensed layouts might have disadvantages.
In order to test this theory signs with (a) the conventional panel layout, (b) signs of the Continental" type with a map of the junction with place names opposite arrowheads, and (c) signs made with numerous names sited one above the other (with arrows indicating the direction) had been compared in terms of reading distance. The total area of each of the experfmental signs was the same. Observers seated in a vehicle driven at 50 m.p.t. had been asked to report the instant at which they, had identified a given name. It had been discovered that the "Continental " signs vvere read at 14 times the distance of the panel signs and the stack type at twice the distance. It was found, however, that when the experiments were repeated for a five-way instead of a four-way junction, observers more frequently made errors with the stack type of sign, usually linking the wrong arrow with a name. The identification was, of course, made from a greater distance than for the other types of sign, and could have been corrected later. But on balance, it was concluded that the stack type of sign was adequate for straightforward cross-road. When a junction tended to be at all complicated the " Continental " type was the best.
On a small sign (e.g., 20 square feet), background colour affects the ease with which the sign is picked out against its background. Tests have shown that the following areas give roughly equivalent target values at a range of 250 yards: 14 sq. ft. yellow, 16 sq. ft. white, 18 sq. ft. red, 20 sq. ft. blue, 22 sq. ft. green, and 36 sq. ft. black. For small signs there arc, therefore, disadvantages in using blue, green or black grounds. Larger signs, especially those on motorways. arc so conspicious that almost an' colour
might be used to give an adequate target value. For large signs there are good reasons for preferring dark backgrounds.
Whatever the size there is some slight gain in legibility both by day and night if the background of the sign is dark and the lettering light. If the sign is to be treated with reflecting material it is Cheaper to reflectorize the letters rather than the whole area of the sign. Large motorway signs may have an area of 400 sq. ft., which with reflective material at 10s. per sq. ft. cost as much as £200, whereas the symbols can be cut out of 62 sq. ft. of material at a cost of 131.
As regards the argument concerning the relative merits of upper-case (capitals) and lower-case lettering for signs, experiments suggested that there were probably advantages in using both upperand lower-case letters for different purposes.
Desirable standards and uniformity of illumination of signs are laid down in British Standard 873 : 1959. Tests recently carried out show that these standards are rarely reached. A new lantern has therefore been designed which enables much greater uniformity to he achieved than hitherto with low power consumption.
Mention was made that, as is well known, European countries, have adopted a protocol in which a series of symbolic warning mandatory and information signs is used. In England, of course, the message is nearly always given in words. Though the Continental signs have been much praised, since they tend to have a tidier appearance, not all of them are entirely satisfactory. In tests, observers were allowed to study a particular sign and then examples of the signs were moved .towards them from a distance. At extreme range they were asked to identify the sips. The following results were recorded: (a) Recognition of sign type (warning, mandatory or informatory) British Continental American Mean values 570 ft. 640 ft. 700 ft.
(b) Identification of the particular sign British Continental American Mean values 210 ft. 240 ft. 200 ft. There were some exceptions to the above results for individual types of sign.