Authors: Fandi Z. Alanazi , Jonathan A. Edlow , David T. Chiu

Abstract

Emergency department crowding remains a persistent challenge across health systems worldwide and is associated with delayed care, increased risk of adverse events, and clinician burnout. Conventional explanations often focus on rising patient volumes or local operational inefficiencies, yet these factors do not fully explain why crowding frequently occurs even in well-resourced hospitals. Queuing theory, a framework from operations research, provides a useful lens for understanding how demand, capacity, and variability interact in complex service systems. When applied to emergency departments, queuing theory demonstrates how high utilization, variability in arrivals and service times, and downstream constraints such as inpatient bed availability can produce sudden congestion and prolonged delays. Viewing emergency departments as networks of interconnected queues helps explain why localized interventions often fail to improve flow and why system-level coordination is required. Although this article focuses on emergency department operations, these principles apply broadly across hospital environments where variable demand interacts with constrained resources. Incorporating queuing theory into health system planning may provide clinicians and administrators with a clearer framework for designing more resilient systems capable of delivering timely care under conditions of uncertainty.

Keywords: Emergency department crowding, queuing theory, patient flow, hospital operations, health systems, review article.