G3 Transition Curve Between Two Straight Lines

This paper describes a G³ transition curve based on quartic Bezier spiral to be used in the design of horizontal geometry of routes. The curve that joins two straight lines will be the composition of spiral-circular arc-spiral forms. It is an alternative curve to traditionally used transition spiral; clothoid. A family of quartic Bezier spiral is defined from analyzing the monotone curvature conditions, and has G³ points of contact properties, which is better than clothoid in terms of smooth transitions regarding to the vehicle-road dynamics. The function of the lateral change of acceleration (LCA) of the curves are applied and illustrated, by means to make the comparison between the transition curve based on quartic Bezier spiral and the traditional transition spiral.