Reported June 2009

TRAFFICKING IN PHYSICS: On a sparsely populated highway, the cars are generally far apart 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 -- in a traffic jam.

WHAT'S UP WITH THIS INTERSECTION: Traffic engineers use multiple techniques to reduce the amount of congestion on busy city roads, from altering the timing of lights to changing the design of intersections. Typically, changes to an intersection are aimed at reducing the number of turn phases at the signal. If the design of the intersection is changed, then the through traffic moves more often, because it is not waiting for a few cars to turn left. This is why some intersections are rearranged to avoid that standard left-turn-only part of the signal. This can be accomplished by moving the left-hand turns away from the main intersection, resulting in intersections with names like Jughandle, Median U-Turn and Continuous Flow.

The Institute of Electrical and Electronics Engineers, Inc.-USA, the Institute for Operations Research and the Management Sciences and the American Society of Civil Engineers contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Gang-Len Chang, PhD
College Park, MD 20742
(301) 405-1953
Gang@eng.umd.edu

Institute of Electrical and Electronics Engineers, Inc.
IEEE
Pender McCarter
IEEE http://www.ieee.org
IEEE-USA http://www.ieeeusa.org
p.mccarter@ieee.org

Institute for Operations Research and the Management Sciences
Barry List
(443) 757-3560
http://www.informs.org
barry.list@informs.org

The American Society of Civil Engineers
Joan Buhrman
Reston, VA 20191-4400
(703) 295-6404
http://www.asce.org
jbuhrman@asce.org

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