Target Luminance in Blowing Snow as a Function of Illuminance Conditions and Visual Range

Abstract

In strong snowstorms, adequate visibility of road delineators provides the driver with important road geometry cues. Few data have been published on the luminance of targets in snowstorms. A model is proposed with which to determine the luminance of an illuminated delineator and the background luminance in snowstorms. An experiment was performed over 30 days in the Ishikari district in Hokkaido, Japan, in 1997. Luminance, illuminance, and transmissivity in snowstorms were simultaneously recorded by a data-recording system at intervals of 10 min. The observation distance was set at 34 m, and snow on the ground was used as the background. The recorded data indicated that the background luminance in snowstorms was affected by illuminance and transmissivity. A multiple regression equation was applied to the model to determine the background luminance. A black board and an illuminated delineator were used as visual targets at the test site. The data indicated that these luminances could be estimated by the multiple regression equation. Differences of the illuminated delineator and the black board in luminance were calculated from these models if the visual range, the observation distance, and the illuminance were given. For example, at a visual range of 200 m, an illuminance of 5000 lx, and an observation distance of 100 m, contrast of the black board was five times greater than that of the illuminated delineator. The results of the study showed that the illuminated delineator indicated good visibility during snowstorms in dark conditions, whereas the black board had a better visibility than the illuminated delineator during snowstorms in the daytime. An illuminated delineator should be located close to the driver to reduce the required luminous intensity. In addition, road delineators should be arranged at short intervals. The data from this study can be used to design and evaluate improved devices of road delineators on highways during snowstorms.

Development of Visibility Assessment Methods with Digital Images Under Foggy Conditions

“…For example, under very bright conditions, the target is very difficult to see even when the visual range is not very low. Hagiwara et al clarified how illuminance of the environment affects the visibility of the delineator in fog (1,2). Based on field observations, they found that the visibility of the target during daytime fog depends on both the visual range and the illuminance of the environment.…”