Congestion

Congestion is the state of overcrowding or excessive accumulation that impedes flow and function in a system. It can occur when demand for a service or space exceeds its capacity, leading to slower movement, longer wait times, or reduced performance. The term is used across disciplines, from transportation to physiology and information technology.

In transportation, traffic congestion describes slow speeds and interruptions to travel caused by high traffic volume, road incidents, weather, or road design limitations. It is typically most pronounced during peak hours in urban areas. Measured by average travel times, speed reductions, or congestion indices, it imposes economic costs through fuel use, time loss, and emissions.

In medicine, congestion refers to the accumulation of fluid or blood in tissues or cavities. Nasal congestion involves swollen mucous membranes and blocked airways, often from allergies or infections. Pulmonary or systemic congestion can occur with heart failure or liver disease. Treatments target symptoms and underlying causes, ranging from decongestants to diuretics and lifestyle interventions.

In information and communications networks, congestion occurs when demand for bandwidth exceeds available capacity, causing packet delays and loss. It can stem from sudden traffic spikes, insufficient routing capacity, or misconfigurations. Techniques to alleviate congestion include traffic shaping, congestion control algorithms (such as TCP), and quality-of-service guarantees.

Policy and planning approaches to mitigate congestion include improving public transit, congestion pricing, demand management, and infrastructure expansion. Measurement often relies on traffic flow metrics, travel-time reliability, or network throughput, and congestion is monitored to inform planning decisions.