A mesoscopic view of speed, flow, density, and distance relationships

Abstract

Traffic engineers have studied speed-flow-density relationships for close to 60 years. However, the debate over the exact relationships for these traffic stream characteristics continues. Although a variety of models have been proposed, none of them appear to describe traffic characteristics under all driving conditions. Thus, a new model is now proposed to explain the travel characteristics under various flow conditions. The new model is termed the mesoscopic model. This terminology indicates the fact that the model considers the microscopic characteristics of the traffic stream while analyzing the macroscopic impact of these characteristics. The model consists of three distinct regimes. The first regime describes uncongested flow. Within this regime drivers are able to achieve relatively high rates of speed and are not severely restricted from passing one another. A second major regime included in the model is the congested regime. Within this regime, the mesoscopic model assumes that drivers maintain a car- following mode. The third and final regime of the mesoscopic model describes traffic flow relationships within the shock waves separating uncongested and congested regions. The mathematical model for the uncongested regime could not be produced during this study due to limitations of available resources. However, a mathematical model for the congested regime was produced and compared to the previous models. The results from this comparison indicate that the mesoscopic model produces