Integrating Multi-Stage Activation Delay and Queueing Effects into EMS Location-Allocation: The QTCMEXCLP Expected Coverage Model

Emergency Medical Services (EMS) must comply with strict response-time standards, yet congestion, queueing, and stochastic ambulance availability can make classical coverage models overly optimistic. This paper proposes the Queueing-based Time-Constrained Maximal Expected Coverage Location Problem (QTCMEXCLP), a probabilistic EMS location-allocation framework that explicitly integrates multi-stage activation delay (call-taking, dispatch, and station readiness), congestion propagation across activation stages, station capacity limits, and a strict time-feasible coverage rule requiring activation-plus-travel time to satisfy a response-time threshold. A queue-adjusted availability measure combines busy probability with a congestion-propagation factor to represent effective readiness under workload. The original nonlinear complementary expected-coverage expression is reformulated using a tractable linear reformulation that preserves conservative coverage estimates, allowing the model to remain computationally efficient for realistic networks. Computational experiments on a synthetic but operationally realistic EMS network (۵۰ demand nodes, ۱۵ candidate stations, ۱۲ ambulances) across ۴۵ scenarios (demand patterns, congestion levels, and fleet sizes) show that, relative to MEXCLP-type benchmark models, QTCMEXCLP increases expected effective coverage by ۱۰-۲۰%, improves compliance with an ۸-minute response-time standard by ۱۱-۲۶%, and reduces uncovered demand by ۳۰-۵۰%. The results indicate that modeling activation delay and congestion propagation can deliver performance gains comparable to adding ۱-۲ ambulances, supporting more resource-efficient and regulation-compliant EMS planning.

کلیدواژه ها:

EMS ، Location-allocation ، Queueing effects ، Activation delay ، Time-feasible coverage