REAL-TIME AMBULANCE RELOCATION MATHEMATICAL MODEL FOR EMERGENCY SYSTEM CONSIDERING MULTIPLE COVERAGE RANGE, RELOCATION COSTS, WORKLOAD LIMITATION,

Emergency Medical Service (EMS) managers are concerned with providing maximum possible coverage in their service area. As emergency calls arrive into the EMS system, some ambulances become unavailable. Redeployment deals with a dynamic relocation of available ambulances so as to compensate for the loss in coverage due to busy ambulances. Real-time approaches aim to select the best relocation plans, taking into account the state of the system at a moment when decisions are made. Unsystematic redeployment can impose superfluous workload and result in unnecessary fatigue for EMS personnel. This paper develops a real-time approach to maximize coverage with minimum possible total travel time, considering accumulated workload restrictions for personnel in a shift. The proposed model considers the coverage of areas by base stations in three coverage ranges and its main purpose is to cover the shortest range. Also, the model considers the workload added to the ambulances resulting from the relocation decision. At any time, ambulances move in such a way that workload on them does not exceed a certain limit. The model is presented with an online approach and some parameters are updated as time changes. The case study in this article is related to the eastern part of Tehran. The population of this area is about 3 million people: its area is 170 square kilometers and is divided into 48 areas. For sensitivity analysis, the relocation problem can be divided into two parts: pre-implementation and post implementation. Prior to implementing the model, depending on the disruption to the system, the location of ambulances may not be appropriate to meet future demands. After running the model, the base of some ambulances may change. Following this change, the extent of coverage of demand points by the bases will change significantly. For this purpose, the criterion is the number of coverage points of demand by base stations within a coverage range of 1r minute.