Modelling co-located servers and dispatch ties in the hypercube model

Several spatially distributed queuing models, notably the hypercube models, have been developed for emergency vehicle service systems. None of these models specifically address the issue of dispatch preference ties that is commonly encountered in systems with co-located units; e.g. ambulance systems. A variation of the hypercube model that accommodates preferences ties is developed and applied to the emergency medical system of Greenville County, S.C.