Different realizations of adaptive cruise control systems (ACC) have been tested. Firstly, only throttle access has been realized. In addition to this, the second realization utilizes access to the automatic transmission ECU. Finally, the third realization includes access to the brakes. Essentially, the first two versions are characterized by different states (e.g. acceleration, hold speed, deceleration), while the third version is based on continuous longitudinal vehicle control, e.g. using fuzzy methods .Practical results showed high system stability for all three ACC versions. Advantages and disadvantages of each realization have been worked out based on simulated and measured results. Measurements showed that the first two solutions are sufficient to handle many traffic situations. However, in comparison with these versions, the third realization turned out to be the most powerful one.