The Closed-traverse Method In The Plane Alignment Design Of Interchange

It is the closed-traverse method which uses the through lines and the alignment units forming the closed-traverse to analyze and calculate when two though lines of some curve combinations in the expressway or the ramp are known. It could be divided into the closed-traverse method of the lines of osculation and the closed-traverse method of the center to center lines of the circles.Based on the revelation of the traverse survey, the closed-traverse method of the lines of osculation regards one curve unit as one beeline's stretching in one direction, and puts forward the design method that the lines of osculation and two through lines known form the closed-traverse. Firstly confirms the lines of osculation which alignment units of the ramp and calculates the length of the tangent line, then orientates the curve units.According to the differences of the curve combinations, the closed-traverse method of the center to center lines of the circles could be divided into the curve combinations including the easements and the curve combinations excluding the easements. The curve combination excluding the easements can be designed and calculated according to the relationship of the sides of the polygon and the relationship between the internal angle and the external angle. The curve combination including the easements is complex, we should firstly know the speciality of the track of the instantaneous center of the circle of the easement(the evolute equation of the easement), Secondly simplify the projection of the instantaneous center of the circle in the coordinate axes, Thirdly calculate using the projection theorem. In the alignment unit parameters confirming and the coordinates of the center of the circles orientating, it need other design methods, such as the mode method, the limited endpoint method.This paper tries to discuss the curve design method of the interchanges in a new way by building the integrated method of the closed- traverse of the center to center lines of the circles.