SCREENING EFFECTS ON ROAD SURFACE-TEMPERATURE AND ROAD SLIPPERINESS

The effect of screening on road surface temperatures during day time conditions is studied. Data from the Swedish Road Weather Information System (VVIS) are used and differences in road surface temperature between sites screened from the sun and well exposed sites are analysed. Six stations in the counties of Skaraborg and Alvsborg are used. The main factors determining the shadow patterns analysed are type and orientation of the screening objects, solar elevation and cloudiness and sky-view factor. The solar elevation and cloudiness determine the potential maximum differences in road surface temperature. While shape and orientation of the screening obstacle determine the occurrence and duration of the shadow pattern. The study shows that the maximum differences in road surface temperature during the day at screened sites are strongly correlated to the daily maximum solar elevation during a given period. It is evident that, when the cloud cover increases, the temperature divergence at screened sites is progressively reduced. The maximum road surface temperature difference occurring during the day has also been shown to have a significant effect on the road surface temperature after sunset at the screened site. The road surface temperature at a screened site is kept at a low level compared with the well exposed station site till after sunset but if the sky-view factor is small the road surface temperature difference can be reduced.