TRAFFICKING IN PHYSICS: On sparsely populated highways the cars are generally well-separated, and can move at whatever speed they choose while freely maneuvering between lanes. A physicist would compare this to molecules in a gas, which are spaced further apart and move around randomly, only occasionally encountering other molecules. During rush hour, traffic density is much greater, so there is less room for cars to maneuver without risking collision, and the average speed is lower. Traffic is more like a liquid at that point. If the density of cars on the highway becomes too great, the flow of traffic freezes up: clusters of a "solid" can form, where cars are packed so closely together they can't move -- a traffic jam.
ABOUT FLUID DYNAMICS: The study of the physics of fluids -- matter in liquid, plastic, gaseous, and plasma states -- is called fluid dynamics. Understanding the behavior of matter under different temperature and pressure conditions is important to applications such as the aerodynamics of aircraft and automobiles, the flow of petroleum through pipelines, weather prediction, and even traffic engineering. Other concepts important to solving problems in this discipline include the velocity and density of a fluid.
The American Mathematical Society and the Mathematical Association of America, The Institute for Operations Research and the Management Sciences, The Human Factors and Ergonomics Society, and the Division of Fluid Dynamics - American Physical Society contributed to the information contained in the TV portion of this report.