November 14, 2008

Some Macroscopic Laws of Urban Traffic Dynamics: Analysis, Physical Evidence and Control Applications


Dr. Carlos F. Daganzo, STC Distinguished Speaker, Director, Center for Future Urban Transportation, Institute of Transportation Studies, UC Berkeley


It is shown that under some conditions some properties of a road link — such as its capacity and its fundamental diagram — scale up when several links are joined together to form a regular structure (e.g., a ring). Of particular interest is the existence of both, a macroscopic fundamental diagram (MFD) relating a network’s space-mean flows, densities and speeds, and a relationship linking the space-mean flows and the number of trips completed.

By following imaginary moving observers that track vehicles we develop simple formulae for the mean flow at any given mean density. These formulae turn out to be the exact MFD for translationally symmetric arterials and rotationally symmetric rings with either signalized or unsignalized intersections. For less regular networks, the result is only an approximation. The formulae depend on the total length and surface area of the network; the average footprint of a vehicle; the distance between intersections; the speed limit; the saturation flow rate; and the method of intersection control. Simulations of San Francisco (USA) and a real-life experiment in Yokohama (Japan) confirm the results. An optimal control scheme that uses the MFD to improve urban mobility will be presented and illustrated with an interactive web-based game.

Biographical Sketch

Carlos F. Daganzo is the Robert Horonjeff Professor of civil and environmental engineering at the University of California, Berkeley. He is Convenor of the oldest international symposium on transportation and traffic theory (the ISTTT) and an Associate Editor of Transportation Research (part B, methodological). Noted for his contributions to econometrics, logistics, transportation operations, network theory and traffic flow, Daganzo has authored four books, “Multinomial Probit: The Theory and its Application to Demand Forecasting” (Academic Press, 1979), “Logistics Systems Analysis” (1st, 2nd and 3rd and 4th eds, Springer, 1991, 1996, 1999, 2005), “Fundamentals of Transportation and Traffic Operations” (Pergamon-Elsevier, 1997) and “A Theory of Supply Chains” (Springer, 2003). Many of Daganzo’s former students hold faculty positions at top ranked schools of civil engineering, business and management, and industrial engineering.  He is now the Director of U. C. Berkeley’s Center of Excellence for Future Urban Transport.