Article ID: | iaor1992340 |
Country: | United States |
Volume: | 7 |
Start Page Number: | 137 |
End Page Number: | 160 |
Publication Date: | Jul 1991 |
Journal: | Stochastic Models |
Authors: | Goldberg J., Szidarovszky F. |
Emergency Medical Service (EMS) systems can be modeled as spatially distributed queueing systems. Each location in the area has a preference ordering for the servers (usually based on proximity of calls to servers). When a call arrives, the dispatcher scans the preference list and assigns the most preferred idle vehicle to the call. If all vehicles are busy, the call is sent to a private ambulance system that operates in parallel to the EMS system. A major problem in designing and operating EMS systems is to estimate vehicle utilizations and busy probabilities for a given set of base locations. In earlier work, various systems of nonlinear equations have been proposed to estimate the vehicle utilization in EMS systems. In this paper the authors present a general model structure that encompasses much of the past work. They develop convergence conditions for the general model and show that a simple bisection method can be used to find solutions. The bisection method also leads to a test for the uniqueness of the solution. The authors demonstrate the method on a problem with 5 vehicle bases and 300 demand locations.