Previous research relating airspace structure and ca-pacity has shown that a decentralized layered airspace concept, in which each altitude band limited horizontal travel to within a prede?ned heading range, improved safety when compared to unstructured airspace. However, the extent of the safety bene?ts of such layered airspace designs were not quanti?ed. To this end, in this paper, con?ict rate models are developed to determine the intrinsic safety of unstructured and layered airspace designs. In comparison to previous work, the present models consider con-?icts between aircraft in different ?ight phases. Thus, con?icts for climbing and descending traf?c, as well as for cruising aircraft, are taken into account when computing the total con?ict rate. To validate the models, fast-time simulations were performed for several different layered airspace concepts, and for unstructured airspace. The results indicate that the models are able to estimate the con?ict rate for high traf?c densities using a model ?t for low densities. When comparing the different layered airspace concepts tested, the model predicted, and the simulation results con?rmed, a clear safety improvement when the permitted heading range per altitude band is reduced. Thus the models can be used to study the effect of airspace design parameters on the safety of unstructured and layered airspace concepts. @en