بررسي تاثير شرايط جوي و بارندگي بر سرعت جريان آزاد و ظرفيت تردد در آزاد راه‌ها: (مطالعه موردي آزاد راه تهران - قم)

A Survey On Weather Condition Effects on Free Flow Speed and Capacity in Freeways (Case Study: Tehran-Qom Freeway

تغيير شرايط پايه رانندگي موجب تغيير در ظرفيت عبوري آزادراه مي‌شود كه به معناي تغيير عملكرد و كيفيت سطح خدمت‌دهي راه است. عواملي كه موجب كاهش ظرفيت مي‌شود را مي‌توان به دو دسته پايدار و ناپايدار تقسيم‌بندي كرد. در اين تحقيق تاثير عوامل جوي (بارندگي) بعنوان يكي از عوامل ناپايدار مؤثر بر سرعت جريان آزاد و ظرفيت در آزادراه تهران-قم بررسي مي‌گردد تا بدين طريق مقدار ضريب كاهندگي بارش باران در منطقه جغرافيايي ايران كه تاكنون مطالعه نشده، تعيين گردد و در صورتي كه ساعت طرح سال آزادراهي در ساعت بارندگي قرار داشت، بابه‌كارگيري ضريب كاهندگي، ظرفيت طراحي تصحيح گردد. بدين منظور تغييرات سرعت جريان آزاد در در دو وضعيت جوي بارندگي و آفتابي مورد بررسي قرار گرفت و با استفاده از تجزيه و تحليل رگرسيون چند جمله اي و اعتبار سنجي داده‌ها از طريق آزمون‌هاي آماري نتايج مورد ارزيابي قرار گرفتند. داده‌هاي ترافيكي و بارندگي مورد استفاده مربوط به 6 ماه انتهايي سال 1391 هستند. نتايج مويد اين نكته است كه بارندگي باعث كاهش5/3 تا 9/8 درصدي ظرفيت و 4 تا 10 درصدي سرعت جريان آزادراه مي‌شود. سرعت جريان آزاد؛ ؛ ؛ آزادراه

Decrease in traffic speed will result in freeway’s passing capacity, and this means decrease in performance level of service quality. Factors resulting in traffic speed decrease are categorized as permanent or temporary. Raining parse is one of temporary factors decreasing free flow speed. In this research effect of weather conditions (rainy weather) are surveyed as a temporary cause of decrease in capacity of freeway and on freeway’s free flow speed in Tehran-Qom freeway. So it can calculate the rain fall decrement index in the geographic region of Iran, (previously not calculated). If the time of traffic considered in design of freeway in the time of rain, by using decrement index the design capacity can be optimized. In this research. In the beginning rainy hour and non-rainy hour were identified and separated, and also hours with less than 0.01 millimeter of rainfall due to insignificant effects were ruled out and considered as non-rainy hour .Studies show that light rain has no significant effect on flow speed and capacity and in some points its effects are neglected. But in case of heavy rainfall due to decrease in driver's vision range and decrease in surface friction between vehicle's wheels and road surface, flow speed will be significantly less than light rain situation and the changes between free flow speed of in 2 different conditions , rainy hour and sunny hour would be calculated. And with use of multi regression analysis and validating data from statistics test, result would be evaluated. traffic data and weather data from the last 6 months of hijri shamsi year 1391 in Tehran - Qom freeway was gathered and results obtained also confirms that rainy weather will result in 3.5 to 8.9 % decrease in capacity and 4 to 10% decrease in free flow speed.