A recursive simulation-optimization framework for the ambulance location and dispatching problem

This study addresses the Ambulance Location and Dispatching Problem (ALDP), which jointly determines the location of available ambulances and their dispatching policy. The latter takes the form of a dispatching list that defines, for each zone of the covered territory, an ordered list providing a hierarchy of ambulances to be chosen whenever a call arrives. While decisions concerning the ambulance locations are of a tactical nature and often based on static information (i.e. average demand), ambulance dispatching is a real-time decision that must take into consideration the current state of the system (i.e. busy and idle ambulances) when selecting the ambulance to respond to the incoming emergency call. Although only few works have considered these two decisions jointly, they all conclude that the system's performance can be improved and the fleet management decisions streamlined by doing so. However, one of the challenges of the ALDP lies in the estimation of the ambulance availability, which has been addressed in previous papers by means of queueing approaches. In this paper, we propose a recursive simulation-optimization framework which encompasses a mathematical formulation for the ALDP and a discrete event simulation model that produces both empirical estimations of the ambulance availability and the system's performance. Extensive numerical experiments on a set of realistic instances show the potential of the proposed approach as an effective tool for dealing with EMS decision-making.