This paper represents a novel smooth trajectory planning algorithm which uses the natural behavior model of a mobile robot (AIR). The shortest path in the free configuration space is obtained by using the visibility, graph method. It is modified according to dynamic constraints which arc implicitly inluded in natural behavior of the mobile robot. The modified path becomes a smooth, easily track-able near time and distance optimal trajectory. For every points of it, translating/steering velocities and accelerations and reaching times are known. It is applicable to the real time dyanamic configuration spaces, because of simplicity and low computational time.