ABSTRACT
Methods of horizontal alignment are composed by using the straight-line and curve method. The straight-line method is the easiest method to use, because the calculation is relatively simple. However, it is difficult to make full use of the circular curve and transition curve. The straightline method cannot deal with the complicated line effectively. The curve method improves the straight-line method, which is setting the wire before the curve. Considering the specifications and the actual requirements, taking the line element as the foundation unit can make the line more fluent. The curve method, according to the requirements of the different line layout, can be divided into the fitting method, building-blocks method, synthetic method, chord tangent method, etc. The idea that the complex horizontal alignment can be composed by several line elements dates back to the 1990s, when the famous studies on this subject were published (Li 1993, Wu 1965). This research field is still quite active (Xu 1997) and the controlled segmentary element design method has been investigated. More recently, Miao et al. (2001) proposed a method for the highway’s horizontal alignment based on the segmentary element. In order to add the new line element, we need to carry out three steps by using the building-blocks method: first, we should determine the curve type and then determine the line element control parameters. According to the dynamic formulation of the end position, the rest of parameters can be calculated.
