Covering models for two-tiered emergency medical services systems

Emergency medical series (EMS) systems commonly consist of two types of providers, basic life support units and advanced life support units, with different capabilities. In contrast to other systems in which multiple vehicle responses are necessary, in EMS systems, the first-arriving unit can begin service prior to the arrival of the second-arriving unit. In this paper, a covering-type model for two-tiered EMS systems is considered. The model, which maximizes the expected number of calls for service that are served adequately, takes server availability into account through a two-dimensional queuing model. Illustrative computational results are provided.