Combining Lanekeeping and Vehicle Following with Hazard Maps

This paper addresses the issues involved with including moving obstacles in a hazard map or potential field framework for driver assistance systems. Under such a framework, control forces must consist of either conservative forces obtained from the gradient of a potential or artificial damping. By treating vehicle following as a combination of a safety distance and a hazard or potential function, common following strategies, such as constant time headway and guaranteed collision avoidance, can be incorporated into this framework without modification. When combining these fields with lateral potential fields for lanekeeping, however, challenges arise due to the natural asymmetry between the longitudinal and lateral velocity of a vehicle. For instance, a decision to change lanes while approaching a slow moving vehicle results in a large amount of undesirable energy transfer into the lateral dynamics. By treating the lateral and longitudinal hazards – described in road-fixed coordinates – as decoupled, however, such transfers can be eliminated. Because of the manner in which the lateral and longitudinal dynamics couple, control with decoupled hazard maps resembles the coupled case when following or lanekeeping while eliminating the problems associated with energy transfer. The paper concludes by discussing the characteristics of the dynamic equations that lead to this result and outlining future work in obtaining rigorous hazard bounds for the decoupled controller.