• emergency medical service;
  • simulation;
  • multiple-unit dispatch;
  • call priorities


Emergency medical service (EMS) systems provide medical care and transportation. While many real-world systems use multiple vehicle types to attend different call priorities, few guidelines exist about which vehicles to allocate in multitiered responses where more than one vehicle is sent per call. This paper makes recommendations for multiple-unit dispatch to multiple call priorities based on simulation optimization and heuristics. The objective is to maximize the overall expected survival probability of patients classified as “life-threatening”. We assume two types of medical units and three call priorities; and that information may be updated when the medical unit arrives on-scene. First, we study the optimal dispatching policies through several examples. Numerical results show that dispatching while considering call priorities, rather than dispatching the closest units, improves EMS system effectiveness. A heuristic algorithm is developed for large-scale problems. A comparison between the heuristic and closest policy is demonstrated using real-world data.