Heavy traffic on highways requires the optimization of inter-distances between vehicles in order to reach time performance and to provide safety solution in transport. Variable spacing and constant spacing are the two policies for the longitudinal control of platoon. Variable spacing doesn't require a lot of data (position, speed...) from other vehicles, and string stability using only on-board information is obtained. However, inter-vehicle distances are very large, and hence traffic density is low. Constant spacing can offer string stability with high traffic density, but it requires at least data from the leader. In this paper, a novel expression of the variable spacing policy has been proposed. It is effective to decrease the distance between the cars, to become nearly equal to the constant spacing policy. It also enables increasing the string stability and the robustness of the control regarding to unmodeled lags, and it can avoid control torque saturation. This novel approach doesn't require heavy communication between the cars. The new control law has been evaluated by simulation with perfect system using Matlab, and with imperfect system using TORCS. The good results have demonstrated the effectiveness of the novel approach.