This paper intends to give a contribution in the field of driver-assist and driversupport systems. In particular, the paper deals with an interface between a driver of a car and a desired velocity with a freely determinable desirable acceleration using a PD/PID-switching controller strategy. This strategy presents the advantage to be easy to implement it. As an operating element, for the control of the function, an usual gas pedal was used. The driver transmits with it his desired vehicle speed to the system. Beside the hard and software structure, it is necessary to develop some regulation functions. Within the scope of this elaboration, the development of these functions are described after the "V-model". Accordingly to this purpose, a model of the system to be regulated is provided at first. For it, a consideration of the transference limbs of the system is carried out at the beginning. Afterwards a basic model of the longitudinal dynamic is put up on the basis of the general tractive power equation as a non-linear state space model. On the basis of the provided model a linearized system is carried. Furthermore the transference behavior of the open chain is analyzed in a Bode diagram. Final validation of the developed functionality is carried out with computer simulations using real data.