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Autonomous vehicle technology is greatly valued nowadays, and an active collision avoidance system is one of the key parts for autonomous driving. This study presents a comprehensive architecture of an active collision avoidance system for an autonomous vehicle, which is integrated with a decision-making module, a path-planning module, a lateral-path-following module and a fuzzy adaptive following module (longitudinal motion) to deal with potential hazards on a straight road or a curved road. In order to make the planned path for overtaking manoeuvres safer, an improved harmonic velocity potential approach for path planning is presented, which innovatively enhances the effect of an obstacle potential on a road by adding a scale term, so that it can generate a smooth path for a vehicle-overtaking manoeuvre. All the potentials which are used for vehicle lane keeping or lane changing are well designed. The lateral-path-following module is based on the constrained linear model predictive control approach, which ensures that the host vehicle can follow the planned path precisely. Furthermore, when the overtaking manoeuvre is not suitable, the fuzzy adaptive following module is utilized to ensure that the host vehicle can adaptively keep a safe distance from the preceding vehicle. Tactical decisions, such as overtaking, accelerating or decelerating, are determined by the decision-making module. Finally, several typical scenarios with low traffic on a straight road or a curved road are simulated to verify the effectiveness and the feasibility of the active collision avoidance system. The simulation results show that the host vehicle can make a successful collision avoidance manoeuvre without the intervention of a human driver in different situations.

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This paper presents an emergency path generation method which could be applied in various driving situations, such as on a straight or a curved road, and in the lane-change and lane-departure scenarios which are the most likely from a traffic viewpoint. It is based on the artificial potential approach and the elastic band theory. The assessment of the emergency path is based on the dynamic performances; the yaw rate and the lateral acceleration of the host vehicle are chosen in this paper. In order to make evasion manoeuvres steadier, a guide potential attached at the front of the obstacle vehicle and a guide potential attached at the rear of the obstacle vehicle are built to affect the moving vehicles in such a way that it encourages the host vehicle to change lane appropriately. Meanwhile, a hazard map of the road environment including the borders and the obstacle vehicles is generated. Thus the forces acting on the corresponding nodes of an elastic band should be zero because of the equilibrium condition; the trajectory with a low hazard is calculated via a numerical method. The simulation results show that the approach is acceptable and leads to a successful collision avoidance manoeuvre in various driving situations.

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