The performance of retroreflective highway signing is entirely dependent on the level of illumination available from the automobile headlighting system. Recent surveys, by the University of Michigan, of both European and United States dipped beam headlamps, provide data on the typical illumination levels available for seeing signs. From this data, using viewing scenario calculations, based vector calculation software, one can readily illustrate the level of sign luminance performance that is currently expected by drivers in the United States and Europe. Sign performance will vary by type of retroreflective material, sign position, distance range considered and vehicle type. Calculations are shown for several material types as well as being presented for several typical sign positions, including overhead and shoulder mounting. The distance ranges considered are representative of those for viewing words and symbols as well as letter legibility. A typical passenger car and typical large vehicle is used. A comparison of the resulting available sign luminance not only clearly illustrates the differences in sign performance between the United States and Europe but also provides a basis for comparing new lighting system designs to typical existing systems. It is recommended that as new automobile lighting systems are engineered, sign illumination be a critical part of their performance evaluation. In addition it is apparent that good signing is a system engineering issue. That is, it is the combination of headlighting and retroreflective performance that makes signs perform well. Thus, from the system engineering view, one could choose higher performance retroreflecting materials to compensate for lower headlight illumination, or choose more headlight illumination on the sign to improve sign performance. For the covering abstract see ITRD E123380.
Samenvatting