A hybrid fleet model for emergency medical service system design

Covering models have been used to locate emergency services such as ambulance and fire protection systems. As an example, in the late seventies, an analysis of the Baltimore, Maryland fire protection system was conducted with the development and use of a covering model called the Facility Location and Equipment Emplacement Technique (FLEET). The FLEET model combined the location of fire stations with the allocation of primary and special service equipment to the stations. Further, in a recent study of Austin, Texas the ambulance system was restructured based on the use of a covering model. Covering models have also been extended to handle some of the special circumstances involved in emergency service systems. One example is the maximal expected coverage problem (MEXCLP). This paper presents a new covering model which utilizes both the special coverage structure of the MEXCLP and the simultaneous station location and equipment allocation of the FLEET model. Optimal solutions are found using linear and integer programming. Results of the model applied to several planning data sets (including a form of the Austin, Texas planning problem) demostrate that more concentrated ambulance allocation patterns exist which may lead to easier dispatching, reduced facility costs, and better crew load balancing with little or no loss of service coverage. Tradeoff curves are presented which show that significant reductions in the number of dispatching sites (keeping the number of ambulances constant) can be made without any major changes in service level.