Traffic signs are part of the road system and their general function is to display information to road users to facilitate the efficient and safe movement of goods and vehicles. If a traffic sign becomes ineffective because of the degradation in its visual properties then the efficiency and safety of the road system could suffer. The materials used on the majority of traffic signs have retroreflective properties so that they can perform adequately during the night as well as the day. Signs don't last forever; all materials will degrade with time and there will come a point at which the sign will be ineffective. Invariably this will happen to the night-time performance first. The paper describes a national daytime describes a national daytime survey of the photometric performance of some 2400 retroreflective traffic signs in the field, and a night-time survey of the photometric performance of 200 retroreflective signs judged to be near the end of their effective life. The data were collected by all six States. The purpose of the daytime survey was to obtain population estimates of the photometric characteristics of traffic signs currently in the field over as large a spread as possible of the age of the signs. The major conclusions are: (1) The photometric performance of Class 1 white sheeting drops to about 80 per cent of its original value after 14 years. (2) The photometric performance of Class 2 sheeting (white, yellow or green) drops to 50 per cent of its original value after 10 years. (3) Cleaning signs improves their photometric performance by about 10-15 cd/lx.m2 at any time along the life-curve. (4) The night-time survey resulted in mean terminal values of 11 cd/lx.m2 for white sheeting, 6 cd/lx.m2 for yellow sheeting, 4 cd/lx.m2 for red backgrounds and 2 cd/lx.m2 for green sheeting, with some values ranging up to 68 cd/lx.m2 Because of the difficulty of making the judgement in the field, these mean estimates are likely to be low (A).
Abstract