Traffic

Traffic refers to the movement of people, goods, and vehicles through a transportation network. It encompasses roads, railways, airways, waterways, and pedestrian flows, with road traffic being the most visible in cities. The analysis of traffic blends engineering, planning, and policy to improve safety, efficiency, and access.

Core concepts in traffic science include flow, speed, and density. Traffic flow is the rate at which vehicles pass a point, typically measured in vehicles per hour. Speed is the average velocity of vehicles, while density indicates how closely vehicles are spaced. The relationship among these variables is illustrated by the fundamental diagram of traffic flow.

Congestion arises when demand approaches or exceeds network capacity, causing slower speeds, queueing, and delays. Bottlenecks at merging points, accidents, adverse weather, and road work can reduce effective capacity. Traffic management aims to mitigate congestion through timing and control devices, incident response, and infrastructure design that improves throughput and reliability.

Management and policy tools include traffic signals, ramp metering, lane closures, speed limits, and urban design that prioritizes transit and nonmotorized modes. Pricing mechanisms, such as congestion pricing or tolling, aim to influence demand. Public transit expansion and land-use planning can reduce single-occupancy vehicle trips.

Measurement relies on sensors, cameras, loop detectors, GPS data, and travel-time apps to monitor conditions in real time. Traffic models, from macroscopic descriptions to microscopic simulations, support forecasting, planning, and evaluation of interventions.

Emerging trends in traffic management include intelligent transportation systems, connected and autonomous vehicles, and greater use of data sharing. These developments seek to improve safety, efficiency, and resilience while promoting multimodal transportation and sustainable urban mobility.