The introduction of autonomous cars will help to improve road traffic safety, and the use of a cargo trailer improves the energy efficiency of transport. One of the critical (collision) road situations has been considered, where immediate counteraction is required in a space that has been only partly defined. This research work was aimed at determining the impact of the trajectory planning method and the values of some parameters of the control system on the feasibility of safe avoidance of an obstacle that has suddenly appeared. The obstacle is assumed to be a motor vehicle moving on a road intersection along a collision path in relation to the autonomous car-trailer unit (CT unit) travelling at high speed. Analysis of cooperation between several non-linear models (representing the car, trailer, tyre−road interaction, and driving controller) has been carried out. Mathematical models of the control system and the CT unit have been built. The process of selection of temporary and variable parameters, applied to the control system for the time of the critical situation under consideration, has been shown. The research work carried out has made it possible to recommend appropriate parameter values for the control system.