In this paper, the ID (identification) of the lateral dynamics of a road vehicle is presented. The mathematical description of lateral dynamics is essential for the development of different autonomous functions. One of the most useful methods to define the mathematical model is the system ID based on measured data. The measurements were performed on straight track sections with an experimental test vehicle. This vehicle is capable of fully autonomous driving. During the measurements, the vehicle’s steering servo was artificially excited while the autonomous function forced the vehicle to drive in a straight line. The input to the system was therefore the sum of the artificial excitation and the control signal from the autonomous function, and the output was the lateral acceleration of the vehicle. The tests were carried out at different speeds. From these measurements, the lateral dynamic system was identified using linear ID methods.