The objective of this work is to examine driver assistance systems, which seem to have a considerable potential for road safety and traffic efficiency improvement, and to propose an impact oriented classification of these systems.  A broad overview of a series of driver assistance systems under development or in some cases already available is presented, which identifies the basic characteristics of each system and its expected impact on traffic efficiency and road safety.  The latter is assessed on the basis of appropriate evaluation criteria. This impact approach, in contrast with the usually adopted user or system oriented approaches, allows for more appropriate identification of the priorities in the field of future research, development and promotion of driver assistance systems.  The proposed classification allocates the driver assistance systems in four different categories on the basis of whether traffic efficiency and safety impact is high or low.  This categorisation reveals that forty percent of the systems considered are expected to have a high safety and low traffic efficiency impact, while only fifteen percent are expected to have both impacts high.