Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
311348 | Transportation Research Part A: Policy and Practice | 2011 | 13 Pages |
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.
► We used a generalized logistic growth curve to model the equilibrium speed-density relationship which is the key to the fundamental diagram of traffic flow. ► The proposed five-parameter logistic speed-density model achieves both mathematical elegance and empirical accuracy which is deemed to be hard to achieve simultaneously. ► The numerical relative error showed that the proposed model yields the smallest error among the models compared. ► The validation results using empirical data from a different site revealed the transferability of the proposed model.