This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Muñoz, J. C. Articles by Daganzo, C. F. Search for Related Content

Structure of the Transition Zone Behind Freeway Queues

Department of Civil and Environmental Engineering and Institute of Transportation Studies, University of California, Berkeley, California 94720
Department of Civil and Environmental Engineering and Institute of Transportation Studies, University of California, Berkeley, California 94720
jcm{at}ing.puc.cl
daganzo{at}ce.berkeley.edu

Observations of freeway traffic flow are usually quite scattered about an underlying curve when plotted versus density or occupancy. Although increasing the sampling intervals can reduce the scatter, whenever an experiment encompasses a rush hour with transitions in and out of congestion, some outlying data stubbornly remain beneath the "equilibrium" curve. The existence of these nonequilibrium points is a poorly understood phenomenon that appears to contradict the simple kinematic wave (KW) model of traffic flow. This paper provides a tentative explanation of the phenomenon, based on experimental evidence. The evidence was a FIFO queue that grew and receded over two detector stations, generating typical flow-density scatter plots at both locations. The locations were far from other interacting traffic streams. The data revealed that a transition zone where vehicles decelerated gradually existed immediately behind the queue. The transition zone was quite wide (about 1 km at both locations), moved slowly (approximately with the "shock" velocity of KW theory), and as a result spent many minutes over each detector station. Disequilibrium flow-density points arose only when the transition zone was over the detectors, suggesting that the transition zone explains their occurrence. The disequilibrium points drifted gradually from one branch of the curve to the other, as KW theory would have predicted if "shocks" had a characteristic width equal to the dimension of the transition zone. Nothing was found in the data to contradict this view. This paper also shows that in our case, if one neglects the shocks' physical dimension, the position of every vehicle can be predicted with KW theory to within approximately five vehicle spacings. Thus, it appears that KW theory can predict rather accurately traffic behavior at the back of FIFO queues, i.e., when the lanes are equally attractive to all drivers. We end with a discussion offering some perspective on how the findings of this paper related to the traffic thinking found in the current literature.

History: Received: August 2000; revised: November 2000; revised: August 2001; revised: December 2002; accepted: March 2002.

This article has been cited by other articles:

				M. Schonhof and D. Helbing Empirical Features of Congested Traffic States and Their Implications for Traffic Modeling Transportation Science, May 1, 2007; 41(2): 135 - 166. [Abstract] [PDF]

				P. Nelson On Driver Anticipation, Two-Regime Flow, Fundamental Diagrams, and Kinematic-Wave Theory Transportation Science, May 1, 2006; 40(2): 165 - 178. [Abstract] [PDF]

				K. Nagel, P. Wagner, and R. Woesler Still Flowing: Approaches to Traffic Flow and Traffic Jam Modeling Operations Research, September 1, 2003; 51(5): 681 - 710. [Abstract] [PDF]