among other places, on the motorway. We see no point in ourselves pursuing further experiments when there is so little choice between alternative areas and legibilities, and while taste plays so important a part, as we believe it should.
Size of Lettering
19. The size of the lettering on a sign is determined by the distance at which the sign is to be read . It is important that the driver should be able to read the sign without having to divert his gaze through too great an angle from the road ahead- hence he must have finished reading it some way before he comes abreast of it. Moreover it takes time to read the sign, and during that time a fast-moving vehicle may have covered a considerable distance. Thus the determining factor in deciding on size of lettering depends as much on the distance at which the driver must begin to read the sign as on that at which he finishes reading it.
20. We believe that the maximum permissible angle through which the driver has to divert his gaze in reading a sign should be about 15°, as used in Germany.[1] As the main motorways will have a three-lane carriageway plus a hard shoulder to the left the centre of the sign may be as much as 50 feet to the left of the driver's path. This means that he should finish reading the sign at least 200 feet before he comes abreast of it.
21. There is evidence[1],[2],[3] that from a direction sign of the kind we recommend in this report a driver takes about two seconds to extract the information he requires. This time may, however, be longer or shorter depending on the order in which he reads the names on the sign . In addition some allowance should be made for the possibility of the sign being momentarily concealed by other vehicles. We think, therefore, that about four seconds, representing a travelling distance of about 400 feet at speeds of 70 m.p.h., should be allowed for reading the sign. Thus the signs must become legible at least 600 feet before they are reached. Since in conditions of average visibility most drivers can read signs at a distance of about 50 feet for every inch of letter height[1],[2],[3] we recommend that the x-height (the height of simple letters such as ' a ' and ' x ') of the lower case lettering should be at least 12 inches.
Colour
22. While the present British standard direction signs use black lettering on a white ground, we have noted that on many motorway signs abroad it has become customary to use light letters on a dark ground. We consider that on large signs such as are inevitable for our purpose here it is not necessary to use a white or light-coloured background to provide adequate target value for the sign as a
- ↑ 1.0 1.1 1.2 Dipl.-Ing. Fritz Heller: 'Regeln zur Bemessung und Gestaltung beschrifteter Verkehrsschilder' (Strassenverkehrstechnik, 1957, 1(12), 75–84).
- ↑ 2.0 2.1 A. Mitchell and T. W. Forbes: ' Design of sign letter sizes ' (Proc. Amer. Soc. Civ. Engrs. 1942, 68(1), 95–104) . 'Unpublished research by the Road Research Laboratory.
- ↑ 3.0 3.1 Unpublished research by the Road Research Laboratory.
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