Trafflow

Trafflow is a term used in transportation engineering and urban planning to describe the movement of vehicles on road networks. It encompasses patterns of speed, density and flow that characterize how traffic distributes itself over space and time. The study of trafflow informs congestion analysis, infrastructure design, and the optimization of signal timing, ramp metering and traveler information systems.

Traffic flow theory distinguishes macroscopic models, which treat traffic as a continuous fluid, and microscopic models, which simulate individual vehicle behavior. The most common macroscopic concept is the fundamental diagram, relating flow q, density k, and average speed v. The Lighthill–Whitham–Richards model and related kinetic or second-order variants describe how traffic density waves propagate, producing phenomena such as shock waves and stop-and-go patterns. Microscopic models include car-following rules that specify how a driver adjusts speed based on the leading vehicle.

Data for trafflow analysis come from loop detectors, GPS traces, probe vehicles, and video or camera systems. These data support metrics like average speed, travel time, queue length and capacity. Applications include traffic forecasting, adaptive signal control, urban planning, and the testing of autonomous or connected vehicle strategies. Modern trafflow research also explores multimodal networks, incident management and resilience under disruption.