Chao Chen

About Chao Chen (Edit profile)

Chao Chen is a graduate student in electrical engineering and computer science at the University of California, Berkeley (

THE ACCESS ALMANAC: The Freeway-Congestion Paradox

Chao Chen and Pravin Varaiya

Traffic congestion on a freeway sets in once the density of vehicles exceeds a certain critical number. Above that, both vehicle speed and vehicle flow drop precipitously. Well-designed ramp meters can limit the number of vehicles entering a freeway, so that critical density is not reached, congestion is avoided and, paradoxically, both speed and flow increase. This double gain of reduced travel time and increased flow far exceeds any improvements that can be achieved by constructing more freeway lanes.

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