Highway geometric design is the first horizontal alignment and vertical alignment design. Highway geometric design provided to motorists is a solid line. Therefore, the horizontal and vertical linear design problem of the linear fit is very important.
1. is the ideal combination of horizontal and vertical position of the vertical curve correspond to each other, slightly longer than the vertical and horizontal curve curves. Or the vertical curve is a straight line segment and no more than a straight line segment.
2. vertical curve radius of horizontal curves and balanced is guaranteed three-dimensional linear coordination, the basic requirements of a smooth, continuous.
3. horizontal and vertical combinations should take into account the driver's vision.