A pilot study was caried out, in which a field method for the measurement of visibility of road markings was tested and visibility distances to road markings were measured. Separate road markings with varying visibility were applied as a centre line on a road. A number of subjects in a car indicated the distance where the line was visible. This distance was then compared with the specific luminance (retroreflection) of road markings. The result shows that the tested field method worked well. The sources of error that can be found when making measurements according to the method in question are discussed in the report. Furthermore, the results show that the visibility of road markings is approximately proportional to the is approximately proportional to the logarithmic specific luminance. This means, for instance, that multiplying the specific luminance by four, from 75 to 300 (mcd/m squared)/lux, increases the visibility distance by 55 % with headlights on and 41 % with dipped headlights. Furthermore, a road marking with the specific luminance of 75 (mcd/m squared)/lux is visible at a distance of scarcely 50 m with headlights on and approximately 40 m with dipped headlights. These results are, however, uncertain as the experiment constitutes a pilot study. (A)
Abstract