| In Japan、 snow accumulation and accretion on beams on the backside of traffic information signs cause problems. The falling of such snow may cause damage to passing vehicles or accidents due to reduction of visibility. Currently、 while snow is mainly removed manually、 measures to reduce such work are necessary. In the past、 focus was placed on a method of facilitating the falling of snow by attaching angled roofs or tilted plates on the beams on the backside of traffic information signs、 and tests were conducted to examine their effect. The results revealed that the amount and duration of snow accretion decreased because the countermeasures made snow fall from the signs earlier. This effect was found to be greater when tilted plates were used instead of angled roofs、 and when the gradient was 60 degrees rather than when it was 45 degrees. However、 there was still a problem concerning the installation conditions as snow accumulated on countermeasures at low temperatures and during heavy snowfall、 in some cases.[*]To clarify the difference in the reduction of the amount of snow accretion by the direction of installation、 a comparative test was conducted using a tilted plate with a gradient of 60 degrees、 which was most effective in facilitating the falling of snow. The countermeasures were installed in a northwesterly direction so as to be facing the prevailing winds head-on、 as well as in a southeasterly direction on the opposite side、 and in a southwesterly direction perpendicular to the prevailing winds. [*]The test results revealed that the number of hours in which snow accretion thickness on the beams without countermeasures was 10 cm or less was about 400、 and that snow fell from the beams three or four times during the period. With regard to the tilted plates facing northwest、 southeast and southwest、 the number of hours in which snow accretion thickness on the tilted plates was 10 cm or less was about 800、 650 and 1、100 respectively、 and snow fell from these structures 22、 17 and 23 times. The tilted plates were effective regardless of installation directions、 and the snow accretion was especially shallow on the installation facing southwest and snow tended to fall from it more frequently. It was presumed that solar radiation also facilitated the falling of snow、 since the temperature of the tilted plate facing southwest was especially high. However、 according to cross-sectional observations of snow accretion、 there were cases where snow cornices developed and the snow accretion thickness increased on the plate on the leeward side facing southeast. Although the installations were basically effective in reducing the amount and occurrences of snow accretion regardless of their direction、 we will have to consider that special attention is necessary when installing tilted plates on the leeward side. |
