This report covers those retroflective signs that depend on headlamp illumination, and provides information on when to replace retroflective signs degraded by weathering. Signs, which are not replaced earlier for other reasons, will eventually lose their night-time luminance and visibility because of weathering. Although it may seem simple to achieve a satisfactory operational level of visibility, this problem is complicated by: (1) the variable nature of the response required by the sign; (2) the surroundings in which the sign is seen; and (3) the luminance provided by the vehicle. Research has identified several factors that help to maintain the visual effectiveness of retroflective signs. Research has been conducted on: (1) the determination of the minimum reflectance which can provide an adequate level of night-time performance; (2) the prediction of the end of 'useful life', so that replacement may be scheduled; (3) methods of inspection; (4) providing an inventory; and, ultimately, (5) systematic method of obtaining the maximum value of each annual expenditure. The principles presented here may be applied to other applications of signing, such as signs used on railways and waterways.
Abstract