Semi-trailer convoys are large, with two-part structures and flexible joints, so the motion when steering is very complex. Lane changing is a common movement process in conditions of high vehicle density. The article establishes a dynamic model of a semi-trailer convoy using the multi-body method and the Newton-Euler equation system combined with the experimental procedure. In the road plane, each structural separation object is described with 3 degrees of freedom: longitudinal, transverse, and vehicle body rotation. The authors used the built-in dynamic model to study the effect of steering frequency on the motion stability of a semi-trailer convoy when changing lanes. The results of the study are used as a basis for optimizing the structure of a semi-trailer.