The Application Of Two Points Element Method In The Interchange Horizontal Alignment Design

Interchange as a widely used road form, should conform with the corresponding terrain, topography, geological, economic conditions and so on, and control routines by the control points strictly. We should make full use of the coordinates of these control points (the start-point and end-point coordinates, the starting point tangent), then draw the horizontal alignment quickly which satisfied with layout in the design. In traditional design, we design interchange by searching two parameters (convolute curve parameter A and final point radius Re) which is too many parameters and hard to converge, in the condition of the start-point and end-point coordinates, the starting point tangent, so in this paper we use two points element as an optimized design in interchange.Firstly, the parameters of the curve are solved by the method of two points element, in the condition of the start-point and end-point coordinates, the starting point tangent, then draw it through the interactive graphic design system quickly. Secondly, we listed the types of interchange and their plane alignment design specifications and standards, accomplished 5 kinds of mainline alignment (line, circle, forward holonomic clothiod, reverse holonomic clothiod, forward nonholonomic clothiod, reverse nonholonomic clothiod, line 1-circle-line 2,) and 7 kinds of ramp alignment (basic type, S type, oval type, convex type, C type, complex type, compound curves), in the condition of both tangent and curvature continuous or tangent continuous but the curvature not, through the method of two points element. Finally, The two points element method is applied to the Tianjin Outer Ring Road-Jin Han Expressway combination interchange engineering, and contrasted with traditional interchange graphic design software——Hint CAD.The paper concludes that two points element method can be applied to the horizontal alignment design of the main line and ramp of interchange. But this method cannot dynamically adjusts the curve parameters which limited by single direction design. Moreover large accumulated errors will be produced by design process, which influences the design efficiency to some degree.