Research On Alignment Combination Method Of Expressway Growing Continuous Longitudinal Slope Based On Operational Safety

Due to the restriction of terrain and environment,the design and decision-making requirements of long and continuous longitudinal slopes are generally needed in mountainous expressways.The long and continuous longitudinal slope section has the characteristics of large altitude difference,small turning angle,high proportion of bridges and tunnels,and many limiting factors of horizontal and vertical alignment,so the road operation safety risk is high.Aiming at the alignment combination of long and continuous longitudinal slopes,the following studies are carried out using theoretical analysis,real vehicle test,numerical simulation,etc.First of all,through field investigation and data collection on the long and continuous longitudinal section of a typical mountainous expressway,the operational safety characteristics of the long and continuous longitudinal section of the mountainous expressway are systematically analyzed from the perspectives of people,vehicles,roads,and environment.On this basis,On this basis,to study the factors influencing the safety of road operations and the basic theories and characteristics of driver’s visual behavior.Then,combined with the safety characteristics of expressway operation,the typical long and continuous downhill section of expressway is selected,the heavy-duty truck is selected,and the eye tracker and other equipment are used to carry out the real vehicle test of the long and continuous downhill section of expressway with the driver’s visual behavior and vehicle operation status as the main research object.Secondly,based on the real vehicle test data,the road alignment indicators of long and continuous longitudinal section are divided into sections,so as to analyze the visual behavior characteristics of drivers in long and continuous longitudinal section.Using the principal component analysis method,the calculation model of driver’s visual load intensity is established,and the safety threshold is divided by the critical values of driver’s visual load intensity of 5.16 and 7.23.Based on the theory of driver’s visual load intensity,this paper studies the combination method of longitudinal slope and horizontal and vertical alignment.The results show that the gradient difference of adjacent slope sections should be controlled within 1.5%and 2.3%when the condition is limited.The concept of straight slope and curved slope is introduced.The straight slope of the long and continuous longitudinal slope section should be controlled within 0.02 as much as possible,the curved slope should be controlled within 0.25,and within 0.45 when the conditions are limited.Finally,based on the real vehicle test data,the influence of longitudinal slope,horizontal curve radius and horizontal vertical combination on vehicle braking frequency is analyzed.The temperature rise prediction model of freight car brake drum in continuous downhill section is selected to analyze the sensitivity of influencing factors on the temperature rise of freight car brake.The temperature rise characteristics of brake drum under different longitudinal slope combination methods are studied.By optimizing the longitudinal slope combination design,the brake drum temperature of freight car can be controlled within 200℃ or 260℃.Based on the trucksim simulation platform,the model of Kangding Luding section of Yakang Expressway and 51km long continuous downhill section of Yaxi expressway is simulated.The distribution characteristics of braking moment of freight car driving in long continuous downhill section are studied,and the line shape combination design of long continuous downhill section is optimized.Finally,from the point of view of reducing the driver’s visual load and ensuring the brake performance stability when the truck goes down the slope continuously,the alignment combination design optimization recommendations for the long continuous longitudinal slope section of the expressway are proposed.Through the research on the alignment combination and design optimization method of the long and continuous longitudinal slope section of the expressway,it has theoretical guidance and practical significance for the alignment design and safety evaluation of the long and continuous longitudinal slope section of the expressway.