In this study, the distance control system of the ACC system was tested via two different controllers. The first controller is the PD controller which tries to keep the distance between vehicles according to the reference distance. Moreover, the second controller is the CTG controller which tries to keep the time gap between vehicles according to the reference time gap. The simulations were done via MATLAB/Simulink. Results show that the PD controller provided smoother transitions with less error however, the CTG controller provided sharper transitions with more error. Therefore, the ACC system which was developed with the PD controller could be much safer and comfortable than the CTG controller.