A dual-mode (cooperative and non-cooperative) collision avoidance radar is proposed. The cooperative mode of the radar is based on tagging cooperating vehicles and other potential highway hazards with modulated fundamental frequency reflectors. The range of the radar when looking at tagged targets is approximately 100 metres. Targets that do not carry tags are also recognized by the radar. However, in order to minimize the “false target” problem, the range of the non-cooperating mode of the radar is restricted to a few metres.