Page:Traffic Signs for Motorways (1962).pdf/21

 respectively vertical rolled steel joists and reinforced concrete pillars, which are made in various lengths, tapering at the rear towards the top. In both cases purlins are clipped to the front of the supports and the signs are clipped to the purlins. We understand that the sign manufacturers are satisfied that either method affords adequate flexibility in the actual erection of the signs. For our part we prefer the concrete to the steel pillars, and we recommend that this form of mounting should be adopted as standard for all large motorway signs.

32. We understand that the smaller signs will have the more conventional type of steel support, and we would recommend that such supports should be painted the same colour as the backs of the signs (see paragraph 24 above).

33. The latest German signs, which are comparable to those we now recommend, are very slightly tilted backwards at an angle of about 1 in 80 from the perpendicular. In addition the signs are sited at right-angles to the road, or even at a slightly greater angle. These measures are taken to eliminate specular reflection, or shine, from headlight beams back on to the road, and we suggested in our interim report that their advantages should be tested with the experimental signs on the Preston By- Pass.

34. The signs on the Preston By-Pass are at present at right-angles to the road and are vertical, and specular reflection on to the road has been observed from them. The Road Research Laboratory have made measurements of the alignment of the four largest signs on the By-Pass and of the degree of specular reflection observed. It is apparent that it is unnecessary to deflect the signs both laterally and vertically, and since we understand that small specified inclinations to the vertical plane present a difficult problem of erection we consider it sufficient to rely on a lateral deflection to eliminate shine. Though it is also apparent that except on left-hand bends signs at right-angles to the road will tend to reflect light away from the road, even on straight roads some lateral angling of the sign will probably be necessary to prevent reflection back on to the road from irregularities in the surface of the sign. The Road Research Laboratory have accordingly recommended that all signs should be erected in a vertical plane but that on straight sections of road and on right-hand bends they should be turned laterally away from the road through an angle of 2°-3° from the normal, and on left-hand bends through one of 2°-3 ° from a line at right angles to a chord drawn from the site of the sign to a point an equal distance from the edge of the carriageway and 600 feet in front of the sign. We endorse these recommendations.

35. Our members who visited the Continent also observed that the majority of the motorway signs seen there were mounted too close to the ground, so that the lower parts of the signs were often hidden by vegetation or defaced by road dirt. The signs themselves could also too easily be obscured by another vehicle. We suggest that the bottom edge of all signs should where possible be not less than five feet above the level of the carriageway.

36. It has been suggested that motorway signs should be duplicated, one on either side of the carriageway, but in general there will be insufficient room on the central reservation for the erection of signs there as is done on some of the