Optimal Assignment of Emergency Response Service Units With Time-Dependent Service Demand and Travel Time

This article formulates an improved integer-programming model to assign multiple types of emergency response service units among their candidate base stations to maximize the coverage to the critical infrastructures, subject to station capacity, service time, and reliability constraints. Unlike past models, this new model formulation accounts for the fluctuation of travel time and demand frequency at different time periods of a day. The potential applications of the model have been illustrated via a case study of assigning firefighting units and ambulances in the city of El Paso, Texas. This article also demonstrates how the model can be modified for the selection of a new base station, increase in fleet size, station capacity expansion, or a combination of these.