Study On Design Indexes Of Steep Slope And Gentle Slope Of Expressway In Zhejiang Province

In order to adapt to complex terrain conditions in mountainous area,the design of expressway often appears continuous longitudinal slope,but the continuous longitudinal slope is not single,due to the need to overcome altitude difference and not extend the length of the route,and to meet the safety and reasonable driving of trucks,the design of continuous longitudinal slope section adopts the alternation of steep slope and gentle slope.The existing research on gentle slope at home and abroad is not mature,when designers design mountain continuous longitudinal slope section,there is no scientific and reliable support basis for the selection of gentle slope index,so there are many hidden dangers in the design of continuous longitudinal slope section.So,research on the design indexes of steep slope and gentle slope of expressway,combined with the present actual traffic situation,providing theoretical basis and technical guidance for the construction of Mountainous Expressway.In this paper,the vehicle speed characteristics and driving behavior characteristics are analyzed through the measured vehicle speed in uphill section,the influence of slope grade and length on the capacity is analyzed,the model of the relationship between the decrease of the speed and the traffic accident rate is established.Through the traffic accident type statistics,the main traffic type are determined in the downhill section,the running speed characteristics of trucks and the relationship between the slope grade and the traffic accident rate in the downhill section is analyzed according to measured data.By the investigation and experiment of truck’s speed on typical expressway uphill in Zhejiang Province,put forward the power-to-weight ratio of the leading vehicle is 7.04 ~ 8.43kw/t,and it should be close to 7.63 kw/t,referencing truck industry development status,type distribution,load distribution,the forecast of expressway traffic composition in the future,and provisions of the state on the external contour size,axle load and quality limit of truck,determining the leading vehicle is Six axis combination vehicle,total weight and the power-to-weight ratio of which is 48.805 t and 7.58kw/t.Based on the theory of automobile dynamics,the climbing performance curve of the leading vehicle was calculated and plotted.Initial speed of steep slope is determined based on measured data,the limit of slope grade and length of expressway are calculated and put forward with analysis of reduced speed and minimum allowable speed of truck.The design index of uphill gentle slope is obtained based on recovering speed and the climbing performance curve of the leading vehicle on the uphill gentle slope section.The design index of downhill gentle slope is obtained based on lowering speed and the braking performance curve of the leading vehicle on the downhill gentle slope section.Comparing the difference between the integral subgrade and the separated subgrade,the design indexes of the gentle slope of the integral subgrade and the separated subgrade are put forward.