Cooperative safety using vehicle-to-vehicle and vehicle-to-infrastructure communication enables warning systems to take into account more detailed and longer range information than previously possible. Due to the increased prediction horizon tactical concepts such as traffic rules and driver intentions must be modelled in addition to short term kinematics traditionally used in driver alert systems. We propose a cooperative warning system that models such concepts using artificial potential fields taking into account multiple route-choice hypotheses. The system is being implemented on the hardware and software platform of the European CVIS project and will be used to evaluate the feasibility of using the history of route-choice estimates as an indicator of unpredictable driver behaviour.