| China is a vast country. Overall, the terrain sloping downward from west to east, isroughly three ladder-like distribution. The eastern terrain is flat, mainly based on plain areasand hilly areas. Terrain in the western region is complex and varied, formed a variety oflandforms such as rolling mountain areas, relatively lower basin areas, agricultural oasis area,vast grasslands area, barren Gobi desert area and cold plateau pastoral areas,etc, by theinfluence of wind, rain, temperature and other weather conditions and human activities.Different landforms bring different environment conditions to the highway construction inwestern region, the design parameters of highway longitudinal grade need to choose differentindex values with the relevant environmental conditions. While, the current highway designspecifications gave the descriptions of maximum longitudinal slope in different speeds andthe discount value of longitudinal slope in plateau area, it just gave the explanation for theaverage longitudinal slope of secondary and lower grade highway, but it did not have guidingsignificance to expressway designing of different landform environmental conditions.Therefore, the study on the average longitudinal slope of expressway in western region withdifferent landforms brings application value to expressway construction in western region.Morphology in the western region of this study is mainly about Gobi desert area andmountain areas, taking Sinkiang’s central area (Hami to Yining)as the study background, thenatural geographical conditions, climate, population, economic and traffic characteristics areinvestigated, based on road traffic, traffic composition, accident data of Urumqi-Kuitunexpressway and correlative road, combined with the development trend of future models,typical type of van type truck, DongFeng EQ5208XXY2, is chosen as the experimentalmodel. By analyzing the performance of vehicle dynamic and braking, the related technicalparameters of test models was determined. Based on the landforms of this study, researchedmainly from two aspects, road traffic capacity of upgrade section and traffic safety ofdowngrade section, carried traffic simulation of capacity by VISSIM software, collected alarge number of data when the test vehicle running on the test road to analyze traffic safety ofupgrade section, temperature predicting model along with the slope and the slope length variation without auxiliary brake conditions was raised by the regression analysis method.Combined with the traffic safety of downgrade section and the traffic capacity of upgradesection, considered synthetically, limit index values of the average longitudinal slope andslope length of expressway in Gobi desert area and mountain area of western region andprinciples of selection of the average longitudinal slope design standards were put forward,moreover, some reasonable suggestions of road safety measures were given. |
