Research On Optimization And Simulation Of Freeway Interchange Export Ramp Alignment

With the gradual improvement of China's freeway network,traffic safety situation is very grim.Freeway accidents are much more severe than ordinary highway.Moreover,interchange of freeway is more accident-prone.Usually,the limited and inconsistent interchange ramp alignment can make drivers inadaptable and vehicles out of control,which cause traffic accidents.Among ramps,the export loop ramp has the lowest alignment indicators and the worst security situation.Therefore,it's necessary to study the optimization of export ramp design based of safety.This paper builds the export ramp alignment safety model by analyzing the relationship between ramp alignment and traffic safety.Then,it operating the simulation optimization on export ramp alignment based on genetic algorithm.First,this paper summarizes the research results of safety design and optimization of ramps of interchange at home and abroad.After the analysis of the main features of types of ramps,the export loop ramp is found out to be the most unfavorable alignment of all.Its operating speed characteristics are studied in detail.Then,this paper researches the impact of the characteristics of plane,longitudinal alignment and superelevation of ramp on traffic safety,and put forward the design points of ramp safety design.Secondly,based on operating speed coordination,three-dimensional linear consistency,sight distance and drivers' tension,eight indicators are selected to analyze the influence of ramp alignment on traffic safety and then their mathematical expressions and evaluation criterions are proposed.Based on these indicators,this paper builds the safety evaluation model of export ramp alignment.Afterwards,the weights of the evaluation indexes are fixed based on the analytic hierarchy process(AHP).Thus,the calculation model of ERSI——the comprehensive evaluation index of export ramp is defined.Then,this paper analyzes the feasibility of applying the genetic algorithm to the optimization of export ramp alignment.The design model of export ramp is established,and the design variables are determined.Binary coding is utilized to realize the coding of aliment design model.Next,the constraints of the export ramp are analyzed and mathematically,which means the range limitation of the constraint variables and the position constraint of the ramp alignment.According to the safety evaluation model of the export ramp alignment,the fitness function of genetic algorithm is established.Finally,referring to the conventional genetic algorithm,the operation steps and processes of the genetic optimization algorithm are proposed.Its control parameters are in discussion.Finally,the simulation optimization on the basis of the genetic algorithm is operated.In this paper,the initial optimization scheme is designed by the experimenter.The optimal combination of alignment parameters is obtained by running the genetic algorithm program after determining the boundary condition of the instance.The result shows that the optimized exit ramp is more secure than the initial design scheme.The simulation result indicates that the genetic algorithm can be applied to the safety optimization of the ramp parameters,which provides a new technical means for the designers to design a safer and more comfortable ramp.