Many ideas have been proposed to reduce traffic congestion. Driving a platoon of vehicles with constant spacing seems to be a promising idea as it increases traffic density. But keeping constant inter-vehicle spacing requires very reliable communication. Another control policy is to drive the platoon with a time headway between vehicles. It is a robust and well known policy but large inter-vehicle distances in addition to weak stability (unity error gain) near low frequencies make it less practical. We have proposed in [1], [2] a modification of the Constant Time Headway policy (CTH). This modification largely reduces the inter-vehicle distances using only one information shared between all vehicles. In this work, we propose an additional modification of our control law. This modification makes our control law similar, in form, to the classical constant spacing policy, but it requires to share only one information between the vehicles. This modification improves the stability of the platoon and removes the weak stability of the CTH near low frequencies. We prove the robustness of the control law in the presence of actuating lags, sensing and communication delays. This proof can also be used to prove the stability of the classical constant spacing policy in the presence of all previous delays, which makes our result more general than those established in the literature. Safety is also discussed and the maximum acceptable communication delay without losing safety is determined. Simulations have been done in many critical scenarios.

Finding solutions to traffic congestion is an active area of research. Many ideas have been proposed to reduce this problem, among of this ideas is moving in platoon. The constant time headway policy (CTH) is a very important platoon control policy, but it is too conservative and induces large inter-vehicle distances. Recently, we have proposed a modification of CTH [1], [2]. This modification reduces inter-vehicle distances and makes CTH very practical. This paper focuses on the control of platoons in urban areas. To control the vehicles, we assume that the longitudinal and the lateral dynamics are decoupled. We take into account a simplified engine model. We linearize the two dynamics using exact linearisation technique. Then, we use the modified CTH control law, adapted to urban platoons, for the longitudinal control and the robust sliding mode control for lateral control. The stability and the safety of the platoon are also studied. The conditions of stability of homogeneous and nonhomogeneous platoons are established. The conditions to verify the safety of the platoon for the longitudinal control (assuming stable and accurate lateral control) are exhibited. The weaknesses (large inter-vehicle distance, weak stability near low frequencies) of the CTH are solved. The improved performance and the safety of the platoon are verified by simulation using TORCS (The Open Racing Car Simulator). A platoon consisting of ten vehicles is created and tested on a curved track, keeping a small desired intervehicle distance. The stability and safety of the longitudinal and lateral controls are tested in many scenarios. These scenarios include platoon creation, changing the speed and emergency stop on straight and curved tracks. The results demonstrate the effectiveness of the proposed approach.

Optimizing inter-vehicle distances is very important to reduce traffic congestion on highways. A modification of the constant time headway policy (CTH) has been proposed in [1]. This modification significantly reduces inter-vehicle distances, but this reduction in the inter-distance may increase the risks of collisions. In this paper, the safety of the modified CTH applied to a homogeneous platoon is addressed. Many critical scenarios are discussed, including hard braking of the leader and followers in the event of communication loss. Safety conditions are presented. In addition, a method to find the maximum allowed delay to inform all the vehicles about communication loss, is also presented. Simulations have been run with 10 vehicles to check safety in the proposed scenarios.

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.