Cooperation of cars capable to communicate bears a high potential with respect to safety in critical situations. Following a top-down design, cars form cooperative groups, exchange information available to them and establish a common relevant picture upon which critical situations are detected, optimal decisions for the groups are derived and are distributed in form of individual action sequences. This paper focuses on the formation of cooperative groups. To this end, a graph-based spatiotemporal distance measure is developed, using the concept of virtual meeting points within the road infrastructure. The distance measure is analyzed and it serves to define cooperative groups of cognitive automobiles.