Research On Several Problems About Reconstruction And Extension Design Of Expressway Interchange

With the formation of expressway network,the reconstruction and expansion of expressway will be one of the important tasks of expressway construction in the future.The corresponding problems in the reconstruction and expansion of expressway interchanges are becoming more and more complex.For example,the small clear distance of interchanges,the insufficient sight distance of interchange exit identification,and the insufficient distance between ramp toll stations and characteristic cause problems to the interchange reconstruction and expansion.But at present,the relevant specifications do not give a solution.To provide design ideas and solutions for the interchange reconstruction and expansion in the future,some key problems are studied in this paper,which is of great significance to improve the design level and traffic safety of the interchange reconstruction and expansion.According to the reconstruction and expansion project information and related research documents,the principles and preliminary work of the interchange reconstruction and expansion are summarized.The influencing factors of the interchange program are analyzed.The reconstruction and expansion plans are divided into in-situ expansion,in-situ new construction,in-situ reconstruction and displacement reconstruction based on the location and form of the changes in the process of reconstruction and expansion of interchanges.Some key problems encountered in the process of the interchange reconstruction and expansion are analyzed according to the independent interchange and the small-spacing interchange.Taking the small distance between interchanges and the small distance between tunnels and interchanges as the research objects,the rationality of the commonly used calculation methods in small distance is compared and analyzed.Two solutions and applicable conditions for the interchange reconstruction and expansion when the clear distance is insufficient are put forward by analyzing the influencing factors of the two kinds of small distance.In this paper,the reasons and types of insufficient sight distance of exit identification in the process of interchange reconstruction and expansion are analyzed.By analyzing the driving behavior of drivers at interchange exits,the calculation model of recognition sight distance at the exit of interchange is established based on the traffic flow theory.After comparing the calculation results with the current specifications,the recommended values are proposed as the basis for judging the insufficient sight distance.According to the types of insufficient sight distance recognition,the plans and solutions for the reconstruction and expansion of the interchange exit were respectively proposed.For the road section which is difficult to identify the sight distance,the measures are put forward to ensure the exit safety.Based on the traffic flow theory,the calculation models of the minimum distance between the center line of toll plaza and the off ramp and merging points,the minimum distance between toll plaza center line and intersection are established by analyzing the driving characteristics of vehicles entering and leaving the ramp toll station.The values of the parameters in the calculation models are analyzed in detail.The rationality of the calculation results is demonstrated by comparing the calculation results with the recommended values in current codes.Finally,the recommended values of the minimum spacing are proposed to provide the basis for the reconstruction and expansion of the toll plaza.