Consider a portion of a road that is straight connecting to another portion of a straight road. If a vehicle is to connect these straight roads, a vehicle would have to make a sharp corner which in practice is impossible. Normally, these straight portions of a road are joined by a smooth curve to make the vehicle motion smooth. This is normally known as horizontal alignment, which is normally simplified by a circle known as simple curve in whose radius is uniform. In a more complicated case, the radius varies in what is known as a complex or transitional curve. This chapter provides you with the skills of computing elements of the simple circular curve. More complicated computations of the complex curve are treated in Chap. 12 .