Abstract
The relations between deflection angle, curvature radius and jerk (rate of change in acceleration) in the design of a road alignment are discussed, and illustrated with diagrams. A curvilinear road alignment is not only more pleasing and safer, but often also cheaper in construction than straight road, because of less moving of earth. The spiral shape of road bends has been firmly established. The deflection and curvature diagrams follow a transition curve, since the ideal curve would allow constant speed driving for each section. A complete curvature diagram for the horizontal and vertical alignment helps in the designing stage of the road.