Investigation the effect of changes in visibility conditions in sandstorms on the selection and limitation of safe traffic speed on the highway

Many studies have been conducted based on field data collected to determine the effects of weather on traffic flow characteristics. However, there are limitations to field data studies that make it difficult to comprehensively assess the impact of weather conditions, especially unusual weather conditions, on traffic flow characteristics. According to traffic police statistics, in the last decade, speeding has been identified as the main cause of accidents on freeways, and therefore speed limits will be the most common retaliatory action by traffic police to prevent these cases. However, few studies have focused on the issue of speed limits in sandstorm conditions that reduce visibility and reduce pavement friction; Therefore, the purpose of this study is to develop a prototype of speed limit theory for roads in sandstorm conditions. For this purpose, in this study, samples of porous asphalt were prepared in the laboratory of Yazd University and after spreading the sandstorm (sandstorm around the desert roads of Yazd province) the amount of friction was measured by the English pendulum test. In general, the results show that the friction rate decreases by about 8.4% when the sandstorm blows due to the scattering of sand particles on the asphalt surface, and consequently the safe speed must be reduced. For example, in a steady field of view (Lv) and a slope (i) of 250 Lv and i = 100% safe speed is also reduced by about 10%. In such a situation, speed limits by electronic signs and traffic police can effectively prevent accidents.