Traffic Flow Diagram Model and Application for "Flow,Speed,Density,and Energy"
The physical essence of traffic flow is the energy-driven displacement of matter.To explore the relationship between traffic flow and energy,this study developed a four-factor diagram that included flow,speed,density,and energy based on the power distribution.In this context,the energy/(kJ·km-1·h-1)was mathematically described as the product of the energy factor/(kJ·km-1·veh-1)and the flow/(veh·h-1).First,the energy factor curve varying with the average speed was established based on the power distribution of the traffic flow at each spatial average speed under equilibrium conditions.Subsequently,the relationship between the speed and the flow was obtained based on four classical traffic flow fundamental diagram models:Greenshields,Greenberg,Underwood,and Van Aerde.Finally,a flow-speed-density-energy diagram was established by combining the flow and energy factors.When the energy conversion efficiency was 100％,the following results were obtained.For speed-energy,as the speed increases,the energy first increases and then decreases because the flow plays a dominant role in the energy changes.For density-energy,the energy exhibits a pattern similar to that of the speed-energy relationship as the density increases;however,the changing pattern is the opposite,as the density is negatively associated with speed.For flow-energy,the energy increases with the flow.A flow value corresponds to two energy values under congestion/non-congestion conditions.Accordingly,the energy factors have two states as the flow increases:The energy factor is increasing or the decreasing rate of the energy factor is lower than the increasing rate of the flow.This study represents a pioneering effort towards formulating refined policies for energy networks and optimizing the design of energy infrastructure.
traffic engineeringflow-speed-density-energydiagrampower distributionenergyintegration of transportation and energy
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