A new model for planning emergency facilities in Shanghai

The response speed of emergency medical services (EMS) is extremely critical for the pre-hospital life saving. For emergency patients, the probability of survival will decease remarkably with each minute passing. Therefore, to provide quick EMS, the location of first-aid stations and the number of ambulances assigned to each station should be carefully designed. This paper focuses on exploring a new method to optimize the distribution of first-aid resources. The double coverage model is partially applied with a new objective function that minimizes expected cost for delayed emergencies plus operational cost for EMS. In the modified model, each minute beyond preset standard is considered as missing time that will result in extra costs, so that patients' emergency demands are much more valued instead of simply "covered". To solve this integer-programing problem, the ant colony optimization algorithm with fine-tuned parameters is applied. In the paper, the plan for ambulance assignment during daytime is studied with a thoughtful constraint considering emergency staffs' workload. In addition, various combos of potential emergency sites are tested to find the best plan for newly built stations with unchanged number of vehicles. The paper turns out that when increasing the number of first-aid stations from 35 (current number of stations) to 50, the total cost will be significantly reduced. This conclusion suggests that the number of first-aid stations plays a more important role in optimization, or in other words, travel time between demands and emergency providers outweighs. The data of this study come from Shanghai Emergency Center.