In designing of original adaptive cruise control (ACC) systems the outer loop is commonly used to control the safe distance between host and lead vehicles, and the inner loop maintains the speed of host vehicle. The aim of this paper is to propose different approach, in which only a single loop is introduced as controller. A decision algorithm for determining a driving mode is designed as part of multistage model predictive control constraints. The nonlinear behavior of vehicle dynamic is represented by a multistage local linear model, which will be identified by using least squares method. The objective of multistage predictive control is to minimized the square of errors between the predicted values of vehicle speed and the safety distance, and their references. The proposed controller demonstrates to more efficient in terms of power computing, it is because the method can keep the optimization control problem as a quadratic programming problem. Some ACC simulation results are given, demonstrating a better performance in terms of distance and speed responses compared to the original ACC system.