Research On Superelevation Design Of Expressway Horizontal Curve Based On Reliability Theory

Since the reform and opening up,China has paid attention to infrastructure construction,and the rapid development of highway has changed the backwardness of highway industry.However,according to the statistics of traffic accidents,the poor situation of traffic safety has not been improved.The number of accidents and casualties is still huge,and people’s property losses are enormous,so the safety problem needs to be solved urgently.Considering the current situation of traffic safety,this study starts with the introduction of the influence factor of road safety and the reliability theory which is used to analyze the reliability of the highway design index “superelevation of horizontal curve”.In detail,the main research achievements are described as follows:Firstly,the influencing factors of traffic accidents are discussed,and the causes of traffic accidents are explored from the four factors which called "human-vehicle-road-environment".The relationship between superelevation and traffic accidents is studied,and the mechanical characteristics of vehicle tires at curve are analyzed.The results show that superelevation has a significant impact on the internal forces of inside tires.The larger superelevation,the higher degree of imbalance.The safety and stability of vehicles running on a curved road with superelevation are analyzed,and the calculation model of superelevation is established under the limit states of sideslipping and capsizing.Secondly,the theory of structural reliability is applied to highway design,and the reliability performance function is established based on the calculation model of superelevation.Then,probability distribution of the random variables including vehicle operating speed,turning radius and lateral force coefficient are calculated according to the reliability performance function.These variables are closely related to the superelevation.The first-order second-moment method is adopted to analyze the failure probability of superelevation based on those calculated probabilities of the random variables.It is found that the failure probability of the maximum superelevation(8%)is high at the design speeds of 120 km/h,100 km/h and 80 km/h.Then,the influence of parameters on the failure probability of superelevation is discussed through quantitative research method.The results show that it is unsafe to improve the reliability of superelevation by changing status of the vehicle.Therefore,the design method based on reliability index is adopted to improve the superelevation reliability.According to the reliability requirements of the corresponding safety classes and reliability indexes of expressway in Chinese code “Unified standard for reliability design of highway engineering structures”,the safe superelevation values are calculated respectively at three design speeds of 120 km/h,100 km/h and 80 km/h.The results indicate that the maximum safe superelevation is recommended to be 6%,which has a high degree of reliability.Next,the simulation software UC-win/Road is used to simulate the three-dimensional scene of the horizontal and vertical combination of small radius curve with straight slope,convex vertical curve and concave vertical curve respectively.The difference of driver’s visual perceptions are compared under different superelevations.Combining with the traffic safety analysis,the maximum resultant gradient of expressway is calculated.It is recommended that the maximum resultant gradient of expressway should not exceed 8% at the design speed of 120 km/h and 100 km/h,and should not exceed 8.5% at the design speed of 80 km/h.Finally,according to the engineering example and the accident data,the relationship among the traffic accident rate per kilometer,the superelevation and the failure probability is analyzed,which proves that the reliability design method of superelevation is safe in the design of horizontal curve of expressway.Reasonable design of highway alignment is the most basic step to ensure road safety.In this paper,the superelevation reliability design method of horizontal curve is the extension and application of reliability theory,which has important reference value and practical significance for improving the level of traffic safety in curved sections.