Distribution Characteristics of Vehicle-Specific Power on Urban Restricted-Access Roadways

The development of new fuel consumption and emission models creates the need to characterize traffic conditions by using vehicle-specific power (VSP) distribution. However, in existing transportation engineering, there has been a lack of knowledge of relationships between the VSP distribution and commonly used traffic parameters and a lack of models to develop the VSP distribution from traffic parameters. To examine how traffic conditions affect VSP distributions, this study uses large samples of floating car data collected from expressways in Beijing to associate VSP distributions with various average travel speeds. After a comprehensive analysis, regular patterns are found between the VSP distribution and the average travel speed. Specifically, when the average travel speed is more than 20 km/h, the VSP distribution comes close to a normal distribution. The mean of the VSP distribution is the VSP value when cruising at the average travel speed, and the standard deviation could be expressed as a power function of the average travel speed. On the basis of these findings, a mathematical model for developing VSP distributions is then derived by using the average travel speed. Finally, an analysis between estimated and actual fuel consumption demonstrates that the VSP distributions developed by the proposed model are applicable for the estimation of fuel consumptions. This study indicates a possibility of developing VSP distributions mathematically for dynamic traffic conditions, which can be integrated practically with traffic models or data for the real-time estimation of fuel consumption and emissions.