The University of Massachusetts Amherst
University of Massachusetts Amherst

Search Google Appliance


Logistic modeling of the equilibrium speed-density relationship

TitleLogistic modeling of the equilibrium speed-density relationship
Publication TypeJournal Article
Year of Publication2011
AuthorsWang H, Li J, Chen Q-Y, Ni D
JournalTransportation Research Part A: Policy and Practice
Start Page554
Date Published07/2011
Keywordsfundamental diagram, Generalized logistic curve, Logistic speed–density model

The fundamental diagram, as the graphical representation of the relationships among traffic flow, speed, and density, has been the foundation of traffic flow theory and transportation engineering. Seventy-five years after the seminal Greenshields model, a variety of models have been proposed to mathematically represent the speed–density relationship which underlies the fundamental diagram. Observed in these models was a clear path toward two competing goals: mathematical elegance and empirical accuracy. As the latest development of such a pursuit, this paper presents a family of speed–density models with varying numbers of parameters. All of these models perform satisfactorily and have physically meaningful parameters. In addition, speed variation with traffic density is accounted for; this enables statistical approaches to traffic flow analysis. The results of this paper not only improve our understanding of traffic flow but also provide a sound basis for transportation engineering studies.