Straight line is one of the elements of plane alignment, which is widely used in road design. For highway reconstruction and expansion, if the length of the straight-line section of the old road meets the technical requirements after reconstruction and expansion, the straight-line section does not need to modify the design, and only needs to design the circular curve part according to the technical standards after reconstruction and expansion. If the length of straight-line section after reconstruction and expansion does not meet the technical requirements, for the curve in the same direction, according to the technical standards after reconstruction and expansion, the adjacent two intersections can be combined into an intersection intersecting with the basic curve, or connected with the elliptical, compound, C-shaped curve and convex shape; for the reverse curve, the radius of the circular curve can be expanded and connected with the S-shaped curve to meet the reconstruction Technical requirements after construction and expansion.